300bhp, 350lbs feet torque 944 3 litre turbo
Discussion
Thanks for that very useful information and support John Mitchell. You are recognised as the expert for building 944 turbo derivatives and I can understand why and your experiences are invaluable. I know that such knowledge comes at a high price (25 years ago I gave up trying to beat everyone else by building the fastest motorcycle racing engines after I recognised the bad impact it was having on my private life) – thanks for sharing it.
Since then we have concentrated on good workmanship keeping engines standard (as Porsche intended) but recently ventured back into engine work to solve the many problems of the Boxster and 996/997 engines to help customers stuck with potentially a very expensive failures and this has lead to an increase in equipment and a return to my love of “engine” engineering again.
Statistics or graphs are very valuable and anyone who has used them knows that a small comparatively inaccurate sweep of any set of figures still provides a strong guide to any trend or conclusion. Anyone can create such graphs from published information and they will show that you can predict rates of acceleration, top speeds, standing quarter mile times etc from a graph plotting power or torque against times or speeds etc with remarkable repeatability. You don’t need to understand the science of engines to do this and it is still very valuable.
At a higher level - although understanding the rules for engines is relatively simple, I don’t think it is being taught by people who understand anything other than the academic side and nothing like the practicality – resulting in the many strange ideas people have – of which the notion that torque is something you calculate from using calculus and engine power and revs is typical.
Yes – for any given revs and power you can derive torque – but what it is – is lost in the academia because practically – torque is by how much a force is being applied to twist something and all the other figures are mathematical calculations derived from it. The average pressure on the piston on the power stroke (or bmep) applied on the area of the piston crown (derived from the unit capacity) twists the crankshaft through the altering radius of the con-rod and the rate of change of speed (or revs) is the result of how much of that pressure (or the resulting torque) is applied to the resistance holding the system back. If you want to argue academically then if torque really was “the rate of change of acceleration” then there would be no torque at constant speed. You could argue that the excess torque needed to maintain constant speed is proportional to the rate of change of acceleration that results - but then that simply agrees with the torque/resistance = acceleration equation again. Can you imagine your young son asking you what torque is when you are tightening a bolt and you answer “it’s the rate of change of acceleration I am applying to the spanner”?
Engines are simple and a good way to simplify what makes them tick is to forget for a minute that pistons go up and down – and imagine it is a system in which air goes in and comes out the other side hotter and that the amount we can get in and out is proportional to the resulting performance. Going into a bit more technical detail – the “time areas” of the ports, the pressure differences on inlet and exhaust sides and the areas of the pipes in and out – govern the performance and looked at like this - a lot becomes easier to understand.
Advanced mathematics do have a value. I have found that if you calculate the “time areas” of the inlet and exhaust valves (for which integration is a useful tool knowing the cam ramp figures and valve sizes etc) and divide by the capacity (to create a specific time area) you will find a remarkably accurate correlation between the resulting torque, power and performance of vastly different engines, enabling output to be predicted at the design stage and showing that it is mass air flow that governs most performance criteria not the specific designs of an individual engine.
Even more useful are the sorts of result John Mitchell provided, from actual tests because if these were plotted on various graphs they would show a similar and straightforward predictability (or correlation), based on actual results.
You could create graphs plotting output against boost pressures, turbo sizes, inlet sizes etc and if you were comparing the results against the same cars with different settings - all the results would show some simple, logical and straightforward rules to reliably predict the results before you embark on risky expense to create something new. This is the essence of science and the core reason for it and using practical results is by far the safest method. The problem is knowing what to try before investing time and money without any results and for this you need to understand the basics that actually work but are not just theory.
If any one part of an engine system limits the resulting performance then changing that one part would always have a big effect while changing something else that is working within its capacity will have a lesser affect. Working out what the limiting factors are is a good guide to where to spend your time and effort and John’s experiences are a big help in confirming some of that.
Basically the bigger the holes and the bigger the pressure differences, the more power you can create.
The problem then is not so much how to create a lot of bhp (which really is relatively easy) but realising that this in itself is not necessarily all that you need to create a car that will perform well.
If the aim is good controllable acceleration between a minimum and a maximum speed – then just seeking to maximise bhp will not necessarily provide the answer as this will inevitably be achieved quite easily with large holes (or valves, valve timing, inlet and exhaust pipes, large turbos or high boost pressures and true compression pressures) at high revs. All these will contribute towards higher bhp – but the aim must always be to first establish the max and min speeds you seek the engine to work within. These will be lower for a short circuit car or a drag racer than an indy circuit car. Then the number of speeds you can use and finally to calculate the rev band your engine has to work within.
After that you can argue about what shape power curve will be best within that restrictive rev band that you must use to the greatest effect – although everyone seems to understand that the best overall acceleration you can achieve by maximising power (or torque) between those revs.
Whether that is best achieved from a flat torque curve or a rapidly rising power graph etc – is much argued about – but never the less each individual creates a shape they seek and the ones that get it right provide the fastest cars.
As maximum torque will always come before maximum bhp - there is always a trade off between them – but the crucial issue is that practically the more you change fixed parameters to increase air flow at high revs, the more you reduce their efficient flow at lower revs – or put more simply, the more you try and increase maximum horse power the shorter the power band and the lower the torque at lower revs – you will achieve. So picking the right parameters to maximise the performance between the revs you are at when you change gear – to the maximum revs you can reach before changing gear again – is the secret and just going for the highest bhp figure you can achieve will not necessarily achieve that.
Porsche have always understood this and created the most torquey engines with relatively flat torque curves and excellent acceleration and understanding the issues have developed turbos and variable engine parameters (varioram, variocam, variable valve lift etc) to find a way to combine big holes and air flow for maximum performance at high revs with good torque at lower revs.
Usually to change a car designed for fast road use to a track car is a big adjustment and to tune an engine requires a lot of expense and patience.
We thought that a standard 944 250bhp turbo had the basic strength to tune and the potential to make faster.
The common route is to increase boost pressure but the downside is too harsh an increase in torque to control easily and a car not so pleasant to drive on public roads or tracks (for track days) unless many other track mods are combined.
With only 5 speeds and ratios designed for top speeds rarely found on tracks, the engine would need a wide spread of power to maximise the relatively large rev range it must be used in and then on top of that it should not spin up the rear wheels too uncontrollably. So an increase in capacity seemed a logical approach since it is cheaper than many other solutions, should increase mid range torque and make the engine more driveable yet if boost pressures were standard should also be relatively reliable and as max revs are not increased, should also be mechanically within limits.
Since with increased revs inevitably comes smaller “time areas” – if you were seeking more top end power - it would be necessary to compensate for this downside by increasing throttle sizes, inlet pipes, exhaust systems and turbo capacity – to increase the revs that the increased capacity worked in - whereas in contrast by aiming to increase power (or torque as they are directly linked) at lower revs - the existing valve time areas, inlet systems and exhaust pipes should be able to cope since there is more time available at lower revs to move the increased quantity of air. And since we were seeking more torque and a wide spread of power – this also fitted that requirement.
Planning to increase torque and power at lower revs and with a wider power band would be no good if we originally were trying to build something to loop a fast race circuit at high speed – but we were not - so the proposition fitted all the criteria and seemed an inexpensive solution to find a huge increase in performance.
Thanks NJH & Diver 944 for totally understanding all this and for expressing it in such a logical and accurate way.
I appreciate all the excellent work done by others like John Mitchell to push the boundaries of the engine even further - but we simply wanted to see if our predictions were right if we put together something we feel Porsche originally probably had in mind – and that others Worldwide could probably copy relatively easily without too much expense to provide something we felt would transform the driveability of the 250 bhp turbo – and so far it seems to have worked out OK.
Mind you after being forced to defend what we have done by the criticism from others – sod’s law would predict our track test will all go wrong and apply a liberal amount of egg to my face since the car has so far only been driven a small distance on public roads and is not set up at all for track driving or even developed – it has literally been bolted together and tried.
For the interest of 333pg333, the car is a standard 250 bhp turbo. The block is 968 as are the pistons (with just scooped out crowns to lower geometric c/r). The gearbox has a std LSD with thicker plates operating at higher torque. It has a 968 clutch plate. The injectors are larger and the ECU has been remapped. The waste gate spring has been replaced with a standard new one. The head is a std 2.7 head and 2.7 camshaft).
Our liners (used in other engines) are cast high strength aluminium heat treated, with Nikasil bores and our fitting system is a cross between wet and dry and our secret for now. I cannot see a problem fitting them to these engines and we are presently making a pattern in house to go ahead.
Getting as bit apprehensive now about or “test session” – no doubt you will all find out how we went on soon.
Baz
Since then we have concentrated on good workmanship keeping engines standard (as Porsche intended) but recently ventured back into engine work to solve the many problems of the Boxster and 996/997 engines to help customers stuck with potentially a very expensive failures and this has lead to an increase in equipment and a return to my love of “engine” engineering again.
Statistics or graphs are very valuable and anyone who has used them knows that a small comparatively inaccurate sweep of any set of figures still provides a strong guide to any trend or conclusion. Anyone can create such graphs from published information and they will show that you can predict rates of acceleration, top speeds, standing quarter mile times etc from a graph plotting power or torque against times or speeds etc with remarkable repeatability. You don’t need to understand the science of engines to do this and it is still very valuable.
At a higher level - although understanding the rules for engines is relatively simple, I don’t think it is being taught by people who understand anything other than the academic side and nothing like the practicality – resulting in the many strange ideas people have – of which the notion that torque is something you calculate from using calculus and engine power and revs is typical.
Yes – for any given revs and power you can derive torque – but what it is – is lost in the academia because practically – torque is by how much a force is being applied to twist something and all the other figures are mathematical calculations derived from it. The average pressure on the piston on the power stroke (or bmep) applied on the area of the piston crown (derived from the unit capacity) twists the crankshaft through the altering radius of the con-rod and the rate of change of speed (or revs) is the result of how much of that pressure (or the resulting torque) is applied to the resistance holding the system back. If you want to argue academically then if torque really was “the rate of change of acceleration” then there would be no torque at constant speed. You could argue that the excess torque needed to maintain constant speed is proportional to the rate of change of acceleration that results - but then that simply agrees with the torque/resistance = acceleration equation again. Can you imagine your young son asking you what torque is when you are tightening a bolt and you answer “it’s the rate of change of acceleration I am applying to the spanner”?
Engines are simple and a good way to simplify what makes them tick is to forget for a minute that pistons go up and down – and imagine it is a system in which air goes in and comes out the other side hotter and that the amount we can get in and out is proportional to the resulting performance. Going into a bit more technical detail – the “time areas” of the ports, the pressure differences on inlet and exhaust sides and the areas of the pipes in and out – govern the performance and looked at like this - a lot becomes easier to understand.
Advanced mathematics do have a value. I have found that if you calculate the “time areas” of the inlet and exhaust valves (for which integration is a useful tool knowing the cam ramp figures and valve sizes etc) and divide by the capacity (to create a specific time area) you will find a remarkably accurate correlation between the resulting torque, power and performance of vastly different engines, enabling output to be predicted at the design stage and showing that it is mass air flow that governs most performance criteria not the specific designs of an individual engine.
Even more useful are the sorts of result John Mitchell provided, from actual tests because if these were plotted on various graphs they would show a similar and straightforward predictability (or correlation), based on actual results.
You could create graphs plotting output against boost pressures, turbo sizes, inlet sizes etc and if you were comparing the results against the same cars with different settings - all the results would show some simple, logical and straightforward rules to reliably predict the results before you embark on risky expense to create something new. This is the essence of science and the core reason for it and using practical results is by far the safest method. The problem is knowing what to try before investing time and money without any results and for this you need to understand the basics that actually work but are not just theory.
If any one part of an engine system limits the resulting performance then changing that one part would always have a big effect while changing something else that is working within its capacity will have a lesser affect. Working out what the limiting factors are is a good guide to where to spend your time and effort and John’s experiences are a big help in confirming some of that.
Basically the bigger the holes and the bigger the pressure differences, the more power you can create.
The problem then is not so much how to create a lot of bhp (which really is relatively easy) but realising that this in itself is not necessarily all that you need to create a car that will perform well.
If the aim is good controllable acceleration between a minimum and a maximum speed – then just seeking to maximise bhp will not necessarily provide the answer as this will inevitably be achieved quite easily with large holes (or valves, valve timing, inlet and exhaust pipes, large turbos or high boost pressures and true compression pressures) at high revs. All these will contribute towards higher bhp – but the aim must always be to first establish the max and min speeds you seek the engine to work within. These will be lower for a short circuit car or a drag racer than an indy circuit car. Then the number of speeds you can use and finally to calculate the rev band your engine has to work within.
After that you can argue about what shape power curve will be best within that restrictive rev band that you must use to the greatest effect – although everyone seems to understand that the best overall acceleration you can achieve by maximising power (or torque) between those revs.
Whether that is best achieved from a flat torque curve or a rapidly rising power graph etc – is much argued about – but never the less each individual creates a shape they seek and the ones that get it right provide the fastest cars.
As maximum torque will always come before maximum bhp - there is always a trade off between them – but the crucial issue is that practically the more you change fixed parameters to increase air flow at high revs, the more you reduce their efficient flow at lower revs – or put more simply, the more you try and increase maximum horse power the shorter the power band and the lower the torque at lower revs – you will achieve. So picking the right parameters to maximise the performance between the revs you are at when you change gear – to the maximum revs you can reach before changing gear again – is the secret and just going for the highest bhp figure you can achieve will not necessarily achieve that.
Porsche have always understood this and created the most torquey engines with relatively flat torque curves and excellent acceleration and understanding the issues have developed turbos and variable engine parameters (varioram, variocam, variable valve lift etc) to find a way to combine big holes and air flow for maximum performance at high revs with good torque at lower revs.
Usually to change a car designed for fast road use to a track car is a big adjustment and to tune an engine requires a lot of expense and patience.
We thought that a standard 944 250bhp turbo had the basic strength to tune and the potential to make faster.
The common route is to increase boost pressure but the downside is too harsh an increase in torque to control easily and a car not so pleasant to drive on public roads or tracks (for track days) unless many other track mods are combined.
With only 5 speeds and ratios designed for top speeds rarely found on tracks, the engine would need a wide spread of power to maximise the relatively large rev range it must be used in and then on top of that it should not spin up the rear wheels too uncontrollably. So an increase in capacity seemed a logical approach since it is cheaper than many other solutions, should increase mid range torque and make the engine more driveable yet if boost pressures were standard should also be relatively reliable and as max revs are not increased, should also be mechanically within limits.
Since with increased revs inevitably comes smaller “time areas” – if you were seeking more top end power - it would be necessary to compensate for this downside by increasing throttle sizes, inlet pipes, exhaust systems and turbo capacity – to increase the revs that the increased capacity worked in - whereas in contrast by aiming to increase power (or torque as they are directly linked) at lower revs - the existing valve time areas, inlet systems and exhaust pipes should be able to cope since there is more time available at lower revs to move the increased quantity of air. And since we were seeking more torque and a wide spread of power – this also fitted that requirement.
Planning to increase torque and power at lower revs and with a wider power band would be no good if we originally were trying to build something to loop a fast race circuit at high speed – but we were not - so the proposition fitted all the criteria and seemed an inexpensive solution to find a huge increase in performance.
Thanks NJH & Diver 944 for totally understanding all this and for expressing it in such a logical and accurate way.
I appreciate all the excellent work done by others like John Mitchell to push the boundaries of the engine even further - but we simply wanted to see if our predictions were right if we put together something we feel Porsche originally probably had in mind – and that others Worldwide could probably copy relatively easily without too much expense to provide something we felt would transform the driveability of the 250 bhp turbo – and so far it seems to have worked out OK.
Mind you after being forced to defend what we have done by the criticism from others – sod’s law would predict our track test will all go wrong and apply a liberal amount of egg to my face since the car has so far only been driven a small distance on public roads and is not set up at all for track driving or even developed – it has literally been bolted together and tried.
For the interest of 333pg333, the car is a standard 250 bhp turbo. The block is 968 as are the pistons (with just scooped out crowns to lower geometric c/r). The gearbox has a std LSD with thicker plates operating at higher torque. It has a 968 clutch plate. The injectors are larger and the ECU has been remapped. The waste gate spring has been replaced with a standard new one. The head is a std 2.7 head and 2.7 camshaft).
Our liners (used in other engines) are cast high strength aluminium heat treated, with Nikasil bores and our fitting system is a cross between wet and dry and our secret for now. I cannot see a problem fitting them to these engines and we are presently making a pattern in house to go ahead.
Getting as bit apprehensive now about or “test session” – no doubt you will all find out how we went on soon.
Baz
hartech said:
Unfortunately all our actual road dyno test results have been carried out in second gear (as they are on public roads and for general safety) so at the moment I only have records for acceleration in second gear to compare between cars. The road dyno takes readings every 1/24th of a second and the results show that our 3 litre turbo in second between 3500 rpm and 6000 rpm is quarter of a second quicker (or 10%) than a standard 944 turbo, 0.6 of a second quicker (or 20%) than a 968 and three quarters of a second quicker (or 25%) than an S2 (and our car is geared slightly higher anyway).
This isn't quite fair to the car. As I'm sure your unofficially aware. The difference between the standard car and a larger capacity 944t in 2nd is marginal (even in my old vastly changed 3.2) when compared to the difference in 4th! 4th in my car used to feel like 2nd in a standard 944T. That should produce some very interesting data!Also for those questioning how fast this would be in the real world. I reccomend a drive! Driving a TVR Cerbera after my 944 felt dissapointing in anything past 3rd and driving the Z4M (no slouch) after getting stright out of the 3.2 944T was like driving an electric golf cart! It felt so flat!
diver944 said:
Hi Patrick, I didn't realise you were on Pistonheads too 
The only thing that Barry has done is change the engine and the mapping, everything else is a standard 250bhp Turbo. It wasn't an exercise to build a max modded turbo, but simply to prove that a 3 litre could be easily built using existing Porsche parts. I'll let you know just how driveable it is, as he's kindly letting me test it on track on Wednesday
If he allows it I'll fix my bullet cam to the inside and get some good video to share
Oh for sure Paul. I know this is done at the budget end of the spectrum but by the sounds of it has yielded good results. I too hope you can get some of this on Youtube or the like. In fact I'd like to see more Lil on there too. The only thing that Barry has done is change the engine and the mapping, everything else is a standard 250bhp Turbo. It wasn't an exercise to build a max modded turbo, but simply to prove that a 3 litre could be easily built using existing Porsche parts. I'll let you know just how driveable it is, as he's kindly letting me test it on track on Wednesday
If he allows it I'll fix my bullet cam to the inside and get some good video to share
Barry,
As an S2 owner (and diehard fan), this thread is really making me think hard about the advantages of turbos. Various chaps on here will know me from the PCGB forum, and will therefore remember my somewhat harsh comments over the years about turbos, but this thread is making me ... ummm ... consider the bank balance, shall we say. For that, I thank you and dislike you, both at the same time!
However, your reason for this conversion seems to be summarised by the following:
I can understand that a larger capacity will reduce torque lag as well, but I thought that this was almost eliminated with a good map too?
Apologies for numpty questions. (You may have answered them already, and I simply haven't understood that which you wrote.)
Oli.
As an S2 owner (and diehard fan), this thread is really making me think hard about the advantages of turbos. Various chaps on here will know me from the PCGB forum, and will therefore remember my somewhat harsh comments over the years about turbos, but this thread is making me ... ummm ... consider the bank balance, shall we say. For that, I thank you and dislike you, both at the same time!
However, your reason for this conversion seems to be summarised by the following:
hartech said:
The common route is to increase boost pressure but the downside is too harsh an increase in torque to control easily and a car not so pleasant to drive on public roads or tracks (for track days) unless many other track mods are combined.
This sounds like a lot of engineering effort to go to just to avoid an over-steep boost increase. Speaking from complete ignorance here, but would it not be possible to write a map that prevents such a fierce increase in torque, thus solving the problem in software (cheap) rather than in hardware (expensive)? Or have I missed something? I can understand that a larger capacity will reduce torque lag as well, but I thought that this was almost eliminated with a good map too?
Apologies for numpty questions. (You may have answered them already, and I simply haven't understood that which you wrote.)
Oli.
Baz, thanks for the reply. You have me intrigued on the wet/dry combo but I completely understand the need to keep that confidential. So are you coating the pistons with a Nikasil finish too? My understanding is that while Nikasil and Alusil are similar, they're not identical...but I stand to be corrected. Do you retain the original cylinders or have you come up with an interlocking system to decrease propensity for flex? We have used a deckplate arrangement on my 3l motor (pic) but I like Jon's system too.
I like how you've integrated the gear ratios with the torque curve and appreciate the need or desire to do so. I have owned one of those more peaky type motors and they do require a certain driving style, not to mention a lot of suspension mods.
Patrick
I like how you've integrated the gear ratios with the torque curve and appreciate the need or desire to do so. I have owned one of those more peaky type motors and they do require a certain driving style, not to mention a lot of suspension mods.
Patrick
Edited by 333pg333 on Monday 9th November 11:17
Edited by 333pg333 on Monday 9th November 11:18
333pg333 said:
Baz, thanks for the reply. You have me intrigued on the wet/dry combo but I completely understand the need to keep that confidential. So are you coating the pistons with a Nikasil finish too? My understanding is that while Nikasil and Alusil are similar, they're not identical...but I stand to be corrected. Do you retain the original cylinders or have you come up with an interlocking system to decrease propensity for flex? We have used a deckplate arrangement on my 3l motor (pic) but I like Jon's system too.
I've always been impressed by that picture around the forums. Lovely finish, didn't realise it was your engine I kept seeing?My understanding of Nikasil and Alusil is that they are very different? Alusil being a 'soft' but very smooth Aluminium finish where a special grinding compound is used to grind away the other elements and leave a layer of only silicone for the rings to run on.
Where as Nikasil (which I'm not so clear on) is a much harder finish and is used as a 'protective' coating applied to give a steel/iron hardness in an aluminium block. Stronger but not as good a finish for the rings to run on?
zcacogp said:
This sounds like a lot of engineering effort to go to just to avoid an over-steep boost increase. Speaking from complete ignorance here, but would it not be possible to write a map that prevents such a fierce increase in torque, thus solving the problem in software (cheap) rather than in hardware (expensive)? Or have I missed something?
Yes. I think you can get basic plug in traction control systems which will electronically dumb down the spike (so that you don't need to spend lots of time and money mapping but whatever you do it means reducing the power
big capacity means deivery is naturally smoother so you can have MORE power and still get more traction....really though it's about rather more than that. The driving experience is totally different to a 2.5turbo. It has so much more power 'off boost' that it just covers ground with infinate ease. Following Paul S in a standard 250 turbo there's a real spooky appearence to the way it just drifts away from you everywhere in the rev range. It's actually visable in the footage taken by John Sims following him at bedford. - don't know where the link is.
Edited by Niffty951 on Monday 9th November 12:19
zcacogb, the problem is that turbos have a dual response - they spin up relative to exhaust flow and pressures. Because you have to lower the geometric compression ratio to avoid detonation (when the engine is running on turbo cylinder filling) - the performance "off turbo" at low revs is usually relatively poor. Then when the turbo eventually finds enough gas flow to start working it sets off a complimentary system whereby the increase in intake delivery is rapidly followed by an increase in exhaust flow that spins it up even harder and if the pressure in the system is set high this change is rapid. Different waste gates and maps can contribute to an improvement but the basic rules remain fixed - if the turbo is powerfull enough to deliver enough air at high revs to produce good power despite the reduced time that the inlet valves are open - then at lower revs - when there is more time - it takes more to spin it up (so is delayed) but once it spins up there will be a shock to the system (which incidentally is partially lost through rapid strain energy entrappment).
Fitting a bigger capacity engine with auxiliaries from a smaller engine will always accentuate the power band towards torque at lower revs and restrict power at higher revs.
Our interest was to see by how much it would flatten the power delivery. We thought that the engine while running almost naturally aspirated at low revs would never the less produce more power at low revs due to the increased pressure drops from the larger capacity engine and also spin up the standard turbo quicker as a result of the increased exhausr flow form the bigger capacity engine at low revs - to increase bottom end torque and reduce the sharpness of the turbo delivery.
We knew that the std turbo can deliver enough air to produce 300 to 320 bhp at higher boost pressures - so although our engine was bigger - that same volume of air - after ignition - would be pushing on an 8% bigger area of piston though a longer stroke so should still produce about 300 bhp at the top end which was ok if the lead up to those peak revs was improved.
We thought the extra capacity would improve driveability and mid range torque by about 20% and reduce the "turbo effect"- but the results - while similar in principle to what we expected - were better in magnitude.
333pg333 our liners have top support flanges to rest on machined faces (similar to those pictured on our web site for 996's www.hartech.org buyers guide etc) and ribs around the outside of the casting to improve hoop stress resistance and heat transfer through greater surface area. The aluminium used has similar strength to mild steel and better heat transfer and the Nikasil bonds better to cast aluminium while the cast surface provides effectively some oil retaining porosity and the expansion rates allow tight piston fits.
Thanks - that's right Niffty 951 - the car should be much more noticeably quicker in the higher gears - partly of course because it is in those gears for longer before changing up and therefore any benefit will apply though more time (more seconds) and be much more noticeable and partly because the resistance is increasing and the extra torque has more of a chance to do its work. Even so I still think that three quarters of a second advantage just in second gear (compared to an S2) should enable anyone to imagine how many seconds in a lap the car should gain.
I have really tried to be modest about all this throughout. I don't think we have done anything extraordinary and I am well aware that others have done more and deserve more recognition. I specifically invited Stuart and others to drive the car as soon as it was running because I didn't want "my opinion" to be downgraded by people anticipating exageration and I wanted a "second party" opinion.
I don't expect the track test to be reported as extraordinary because this was planned as a fast and pleasant road car - improving on the already superb 944 turbo - and its limitations on the track will become obvious and also the drivers are used to cars set up for track driving and may be unable to assess the engine - particularly as it doesn't feel to me all that fast.
I think this is because one thing Ajax 50 said was relevant - about the rate of change of acceleration - and how we interpret the sensation. Once moving we cannot detect constant speed (if our eyes are closed) and steady acceleration is easy to get used to whereas a rapidly changing rate of acceleration feels dramatic. Our turbo does not have that sudden kick from modest to rapid acceleration - it just steadily builds up and then feels pretty constant - which doesn't feel that quick. It is the same problem I had years ago with the 350cc Armstrong GP bike that the riders felt was slow even though they were lapping faster and achieving higher top speeds because it had an even torque spread.
I don't think my initial report that we had completed the engine was too dramatic and I simply expected some interest and responses. I didn't expect reports that it would only do 140mph, there was something wrong with having more torque and bhp up 6K revs by a mile than standard models or the various arguments about what torque is etc and in defending all that and trying to convey to those who may be interested or confused - what actually is important - I think I have inadvertently raised the profile of this whole exercise way above what I intended (or really what it deserves).
It really upsets me to read that so many people who clearly know quite a lot about engines and are interested - have misunderstood so many of the basics and I enjoy trying to explain when they have made mistakes to help them improve their understanding. I appreciate that this makes me come over as a big head and therefore a good target to be shot down - but you cannot be knowledgeable and at the same time convey to others who are arguing with you - without appearing arrogant at times - which I regret.
They say "those that can do and those that can't teach" and it is rare for those "that can" to also try and teach as well and I don't find it easy. However there are some of us that have built engines that performed very well and interestingly all those agree with me about the important issues and technical requirements. It seems only those that think they know it all, but have never put their knowledge to the test, argue so vehemently at times.
I am just really chuffed that the type of performance we anticipated was achieved and with the same ease we expected and there are only a handfull of people who were there before we started and knew what I predicted and they are soon to test out the results.
The ability to predict outcomes and then achieve them is perhaps the greatest test of an engineer and in this respect I am pleased with our creation and that it could be reproduced elsewhere quite easily. I don't feel the need to prove anything as it is a matter of record that the first time a 350cc triple I had built was run around a track (Barry Sheene at Brands Hatch) it broke the lap record, the first time a 500cc engine was raced it was the fastest through the speed trap at the TT, the first International race two of my 500's raced in they were 1st and second (NW 2000), the first time Neil Mckenzie raced my 350 (reported as uncompetitive by team riders) he won by half a lap, the first time my 500 cc square four was fired up and in its first 3 laps round Silverstone (for the British GP), it qualified ahead of the multi million pound Honda four stroke also being raced in public for the first time but after months of extensive development and in one TT sidecar race my engines won both classes.
Yes I am bragging (sorry) but only to reinforce to those interested in learning about engines and fascinated (as I am) by their development, what it is all about and who to trust when the "Internet experts" start stating their theories that are often misleading or plainly wrong. I didn't have any financial resources (other than what I could earn), very little development time, and had to make a living as well as invest time and money in ambitious projects - never having sponsorship back up, the best tyres, the best fuel or the very top riders - so getting it right at the design stage was essential and required a proper understanding of what was really going on.
I am therefore especially pleased some thirty years after these past engine exploits - because we cover these sort of issues here at work in training sessions and it helps my staff to believe in what I tell them (which is often different to what they read, were taught or believed) when things like this work out OK.
I am just a little sorry that what was always been a relatively modest project, that I was happy to slowly progress until someone else with more enthusiasm took over, has attracted so much controversial attention - but you cannot back off in this position once you have inadvertantly got there - and I suppose it makes for good internet reading?
Baz
Fitting a bigger capacity engine with auxiliaries from a smaller engine will always accentuate the power band towards torque at lower revs and restrict power at higher revs.
Our interest was to see by how much it would flatten the power delivery. We thought that the engine while running almost naturally aspirated at low revs would never the less produce more power at low revs due to the increased pressure drops from the larger capacity engine and also spin up the standard turbo quicker as a result of the increased exhausr flow form the bigger capacity engine at low revs - to increase bottom end torque and reduce the sharpness of the turbo delivery.
We knew that the std turbo can deliver enough air to produce 300 to 320 bhp at higher boost pressures - so although our engine was bigger - that same volume of air - after ignition - would be pushing on an 8% bigger area of piston though a longer stroke so should still produce about 300 bhp at the top end which was ok if the lead up to those peak revs was improved.
We thought the extra capacity would improve driveability and mid range torque by about 20% and reduce the "turbo effect"- but the results - while similar in principle to what we expected - were better in magnitude.
333pg333 our liners have top support flanges to rest on machined faces (similar to those pictured on our web site for 996's www.hartech.org buyers guide etc) and ribs around the outside of the casting to improve hoop stress resistance and heat transfer through greater surface area. The aluminium used has similar strength to mild steel and better heat transfer and the Nikasil bonds better to cast aluminium while the cast surface provides effectively some oil retaining porosity and the expansion rates allow tight piston fits.
Thanks - that's right Niffty 951 - the car should be much more noticeably quicker in the higher gears - partly of course because it is in those gears for longer before changing up and therefore any benefit will apply though more time (more seconds) and be much more noticeable and partly because the resistance is increasing and the extra torque has more of a chance to do its work. Even so I still think that three quarters of a second advantage just in second gear (compared to an S2) should enable anyone to imagine how many seconds in a lap the car should gain.
I have really tried to be modest about all this throughout. I don't think we have done anything extraordinary and I am well aware that others have done more and deserve more recognition. I specifically invited Stuart and others to drive the car as soon as it was running because I didn't want "my opinion" to be downgraded by people anticipating exageration and I wanted a "second party" opinion.
I don't expect the track test to be reported as extraordinary because this was planned as a fast and pleasant road car - improving on the already superb 944 turbo - and its limitations on the track will become obvious and also the drivers are used to cars set up for track driving and may be unable to assess the engine - particularly as it doesn't feel to me all that fast.
I think this is because one thing Ajax 50 said was relevant - about the rate of change of acceleration - and how we interpret the sensation. Once moving we cannot detect constant speed (if our eyes are closed) and steady acceleration is easy to get used to whereas a rapidly changing rate of acceleration feels dramatic. Our turbo does not have that sudden kick from modest to rapid acceleration - it just steadily builds up and then feels pretty constant - which doesn't feel that quick. It is the same problem I had years ago with the 350cc Armstrong GP bike that the riders felt was slow even though they were lapping faster and achieving higher top speeds because it had an even torque spread.
I don't think my initial report that we had completed the engine was too dramatic and I simply expected some interest and responses. I didn't expect reports that it would only do 140mph, there was something wrong with having more torque and bhp up 6K revs by a mile than standard models or the various arguments about what torque is etc and in defending all that and trying to convey to those who may be interested or confused - what actually is important - I think I have inadvertently raised the profile of this whole exercise way above what I intended (or really what it deserves).
It really upsets me to read that so many people who clearly know quite a lot about engines and are interested - have misunderstood so many of the basics and I enjoy trying to explain when they have made mistakes to help them improve their understanding. I appreciate that this makes me come over as a big head and therefore a good target to be shot down - but you cannot be knowledgeable and at the same time convey to others who are arguing with you - without appearing arrogant at times - which I regret.
They say "those that can do and those that can't teach" and it is rare for those "that can" to also try and teach as well and I don't find it easy. However there are some of us that have built engines that performed very well and interestingly all those agree with me about the important issues and technical requirements. It seems only those that think they know it all, but have never put their knowledge to the test, argue so vehemently at times.
I am just really chuffed that the type of performance we anticipated was achieved and with the same ease we expected and there are only a handfull of people who were there before we started and knew what I predicted and they are soon to test out the results.
The ability to predict outcomes and then achieve them is perhaps the greatest test of an engineer and in this respect I am pleased with our creation and that it could be reproduced elsewhere quite easily. I don't feel the need to prove anything as it is a matter of record that the first time a 350cc triple I had built was run around a track (Barry Sheene at Brands Hatch) it broke the lap record, the first time a 500cc engine was raced it was the fastest through the speed trap at the TT, the first International race two of my 500's raced in they were 1st and second (NW 2000), the first time Neil Mckenzie raced my 350 (reported as uncompetitive by team riders) he won by half a lap, the first time my 500 cc square four was fired up and in its first 3 laps round Silverstone (for the British GP), it qualified ahead of the multi million pound Honda four stroke also being raced in public for the first time but after months of extensive development and in one TT sidecar race my engines won both classes.
Yes I am bragging (sorry) but only to reinforce to those interested in learning about engines and fascinated (as I am) by their development, what it is all about and who to trust when the "Internet experts" start stating their theories that are often misleading or plainly wrong. I didn't have any financial resources (other than what I could earn), very little development time, and had to make a living as well as invest time and money in ambitious projects - never having sponsorship back up, the best tyres, the best fuel or the very top riders - so getting it right at the design stage was essential and required a proper understanding of what was really going on.
I am therefore especially pleased some thirty years after these past engine exploits - because we cover these sort of issues here at work in training sessions and it helps my staff to believe in what I tell them (which is often different to what they read, were taught or believed) when things like this work out OK.
I am just a little sorry that what was always been a relatively modest project, that I was happy to slowly progress until someone else with more enthusiasm took over, has attracted so much controversial attention - but you cannot back off in this position once you have inadvertantly got there - and I suppose it makes for good internet reading?
Baz
Andy97 that would take some working out and for many different scenarios.
All would require a strip and rebuild - so would be over £1000 before doing anything else.
Starting with a 968 would need pistons modified, a 2.7 head and then all the 944 turbo auxiliaries.
Starting with a 2.7 would already have the head and bores but would need different pistons (possibly modified 968) and a crankshaft, rods etc and all those auxiliaries.
Starting with an S2 would require pistons and the 2.7 head + aux etc.
Starting with a 944 turbo would require cylinder liners, crankshaft, pistons but you already have all the auxiliaries.
Then it depends upon whether we are doing everything or just the engine and all the parts are just delivered for modification and reassembly.
Then again many parts required would have to be sourced second hand and there is a question of finding them, prices etc.
All in all it would be very difficult to fix a price at this stage - but I think the first stage is to manufacture some liners and id someone wants one building with just an engine initially - to take it from there.
Apart from modifying the pistons (that require a lathe) and suplying and fitting liners (if it has a 100mm bore) and finding or supplying shorter head studs in some cases, the rest is well within the capabilities of a "home mechanic"/enthusiast to do themselves.
I expect the mapping could be done reasonably now the parameters have been set.
Baz
All would require a strip and rebuild - so would be over £1000 before doing anything else.
Starting with a 968 would need pistons modified, a 2.7 head and then all the 944 turbo auxiliaries.
Starting with a 2.7 would already have the head and bores but would need different pistons (possibly modified 968) and a crankshaft, rods etc and all those auxiliaries.
Starting with an S2 would require pistons and the 2.7 head + aux etc.
Starting with a 944 turbo would require cylinder liners, crankshaft, pistons but you already have all the auxiliaries.
Then it depends upon whether we are doing everything or just the engine and all the parts are just delivered for modification and reassembly.
Then again many parts required would have to be sourced second hand and there is a question of finding them, prices etc.
All in all it would be very difficult to fix a price at this stage - but I think the first stage is to manufacture some liners and id someone wants one building with just an engine initially - to take it from there.
Apart from modifying the pistons (that require a lathe) and suplying and fitting liners (if it has a 100mm bore) and finding or supplying shorter head studs in some cases, the rest is well within the capabilities of a "home mechanic"/enthusiast to do themselves.
I expect the mapping could be done reasonably now the parameters have been set.
Baz
Perhaps I should just add for clarity that our "liners" are more like replacement cylinders - as the whole of our casting fits in the crankcases and the top (where the coolant contacts it) contacts the outside of our liner directly and not through a part of the old casting in which we have slipped a liner. That's how we can add ribs to increase the strength and the cooling contact area and a solid tube is stiffer than two tubes inside each other. Photo of 996 "liner" on our web site explains better.
Baz
Baz
Baz I guess to touch on some of the dynamics you describe about turbos and their typical response characteristics. Those of us who tend to focus on modified 944 turbos forget that the standard compression ratio of 8:0.1 is low compared to modern cars and also turbos themselves have advanced a lot from the 1970's. With design like twin scroll, extended tips, and of course variable vane technology and materials like ceramics to go with superior bearings, it is getting closer to being able to have your cake and eat it, so to speak. Also with superior engine management systems like Motec and cool burning fuels like E85 we really can have the best of all worlds. By increasing capacity AND all the ancillaries to greatly improve the Volumetric Efficiency in addition to using some of the abovementioned tech, I think there is the capacity to have a very responsive and powerful motor capable of well over 600bhp. The next issue to deal with is traction as you've already touched on.
This is just what's possible and not a slight on your build at all. I salute you and your build and I think for a relatively cheap amount you have made what you wanted, a great motor for a road car.
Patrick
This is just what's possible and not a slight on your build at all. I salute you and your build and I think for a relatively cheap amount you have made what you wanted, a great motor for a road car.
Patrick
Barry,
Thanks for your answer. Very helpful. I have never driven a turbocharged petrol engine of any make, and have always stuck to N/A stuff, hence my ignorance of the finer parts of the dark art of turbocharging ... !
I also note that you could consider this conversion on an S2. I guess that as you are bringing together parts from three different cars (3.0 bottom end - S2 or 968, Turbo ancillaries - Turbo, 2.7 head - 2.7) then you could start with any of the three, but surely the cheapest starting point has to be the turbo, and put a liner in the block? (ETA: That still means you have to find a 2.7 head tho', which is the rare part of the jigsaw ... )
Oli.
Thanks for your answer. Very helpful. I have never driven a turbocharged petrol engine of any make, and have always stuck to N/A stuff, hence my ignorance of the finer parts of the dark art of turbocharging ... !
hartech said:
Our turbo does not have that sudden kick from modest to rapid acceleration - it just steadily builds up and then feels pretty constant - which doesn't feel that quick.
Interestingly, this is the very same criticism that I have levelled at the S2. Smooth and progressive, and you don't get a shove in the back, despite the fact that the car is no slouch. I think my description of the performance was that 'you don't realise you are going fast unless you see the rapid twist of the dials, and see the scenery going past quite briskly.' I also note that you could consider this conversion on an S2. I guess that as you are bringing together parts from three different cars (3.0 bottom end - S2 or 968, Turbo ancillaries - Turbo, 2.7 head - 2.7) then you could start with any of the three, but surely the cheapest starting point has to be the turbo, and put a liner in the block? (ETA: That still means you have to find a 2.7 head tho', which is the rare part of the jigsaw ... )
Oli.
Edited by zcacogp on Monday 9th November 19:31
hartech said:
Can you imagine your young son asking you what torque is when you are tightening a bolt and you answer “it’s the rate of change of acceleration I am applying to the spanner”?
Hi Baz, I have a few questions that I hope will aid in ppl's understanding. In the above statement, I believe the previous poster was talking about acceleration or rate of change of speed. The spanner analogy is an interesting one, if one considers an inertial dynamometer a known mass (drum) is rotating and once per revolution it passes a sensor that registers in effect the time taken to perform one revolution. My understanding is that the inertial dynamometer measures torque by measuring how much faster the drum spins from revolution to revolution, in effect its acceleration as this tells us how much torque had to be applied to accelerate the mass (F = M x A Newtons second law). Power graphs can then be generated using an engine revolutions pickup.hartech said:
Another reverse lack of understanding is Ajax50’s comment that a steep power curve = loads of torque – as really the opposite is true (although to be fair he did support the advantages of torque – perhaps just got a bit muddled up about the graphs). Since power is proportional to torque * revs, if the torque was say a flat line – then the power would increase in a straight line as the revs rise. Since maximum torque is always achieved before maximum bhp, and the maximum possible is in proportion to the breathing capabilities of the engine – any increase in torque before top revs or peak bhp, will make the line higher at lower revs and therefore the bhp line would not be steeper but flatter. Anything that increases top revs and bhp at high revs more (which is the common tuning result) almost always lowers the torque at lower revs and the result again is always a steeper power curve. So once again the stated criticism is actually arse about face!
Hi Baz, me again. I don't think Ajax50 was making a criticism, just a simple observation. I am confused by your commentary above as Ajax50 said nothing about when where or how a steep curve is produced, but if we look at your example above perhaps it will help ppl. You say that if an engine has a flat torque output, the resulting power output is a straight line. Now surely if the same flat torque output was now increased the result is another straight line only steeper? Next one has to consider the whole curve in the examples you give above. The high torque engine you describe will definitely have a very steep power curve but crucially its steep lower down. Relatively speaking if we took the same rpm range the same maximum power but lowered the torque the result is a gentler incline if one is looking for the steepest part of the whole graph of course.
Some more interesting issues to tackle - but linked by torque.
Firstly – look – torque is simply a force – a twisting force – it has no connection with speed or time unless you decide to use it in a formula to create another measurement system using it. Like if you use a few constants and speed to create a reading for power or use some differences in speed to calculate acceleration.
Just because after doing that you can then reverse the formula to work backwards does not mean that when asked what torque is you could say it is something that you get when you have power or acceleration and apply mathematics or calculus to it – it is the other way around – it is the force that results in that power or that acceleration and unless you see it for what it is you will always get muddled thinking about how to use or change it for the best.
I still think the best analogy it to imagine removing the engine and fitting one of those torque spanners that bend against a scale to the prop shaft and then you sit in the engine bay and twist the torque spanner while someone with a fast shutter speed camera, photographs the torque reading on the torque spanner.
If you do not apply enough torque the car will not move – so no work is done, there is no power to calculate and no speed is achieved.
Once you apply more torque the car starts moving, work is done and at any speed you can calculate a figure to compare it to other cars (called power) to establish why some cars in this set up travel faster or further than others.
When you cannot turn the spanner with enough power to accelerate the car – the resistance to motion has equalled the torque applied (i.e. top speed).
When the torque applied is greater than the amount needed to keep the car travelling at a constant speed then the spare extra torque speeds up the rotational speed of the spanner and with it of the car – which is then accelerating (i.e. the rate of change of speed).
A more powerful person may be able to twist the spanner with more force and as a result it will accelerate quicker (as will the car) but this doesn’t mean that the twist he applies is a mathematical figure derived from the power or rate of acceleration – the twist he applies depends on the strength in his arm! Or even the tension in his muscles – just as the pressure acting on the area of the piston through the angle and radius of the con-rod does in an engine.
How much it accelerates depends upon how much extra torque is applied and as T=I*a (or acceleration = Torque/resistance), the more torque you apply the more acceleration results.
However in the above scenario – if we changed up a gear the car would accelerate more slowly because it is the rear wheel torque that accelerates it not the gearbox input torque (or engine torque). It is of course still proportional and anywhere the engine produces more torque it also produces more torque and power at the rear wheel in some proportion – but still the amount available to accelerate the car is increased or reduced by the gear ratio and final drive ratio in use.
So if an overall combined internal and final drive ratio is 2 to one say – the rear wheel torque in that gear will be twice the engine torque at any particular engine or rear wheel speed in that gear (if in this discussion we ignore internal losses as the same for each model or tuning scenario).
Fitting an S2 crown wheel and pinion shaft to a turbo gearbox (or just using the S2 gearbox) improves the rear wheel torque in any gear and at any revs by about 12.5% - so if you don’t need to travel at the original top speeds – is a good move (as the LSD can still be fitted) although it is not as strong a tooth profile and will fail sooner (which is irrelevant for racing I suppose).
However in our particular scenario – because we produce much more torque at lower revs – while a lower overall gear ratio would still improve the torque we have by 12.5% - we already have something like 75% more torque anyway – so it is not so relevant.
Indeed if you compare an S2 with our Turbo – say both changing gear from 3rd to 4th (at around 87 to 93mph) the S2 picks up at about 200 lbs ft torque and our turbo at about 340 lbs ft (engine torque) or 800 lbs ft at the wheel with the S2 or 1186 lbs ft with the turbo).
Similarly if you changed from 4th to 5th at 115mph in the S2 or 127mph in the turbo you would pick up at 200 lbs ft (engine torque 761 lbs ft rear wheel torque) in the S2 and 325lbs ft engine torque (1134 lbs ft rear wheel torque in the turbo.
This is an interesting comparison because if you went from 3rd to 4th to 5th in the S2 but missed out 4th all together in our turbo and went from 3rd straight to 5th (dropping to 3500 rpm) you would also pick up at 300 lbs ft (engine torque), the rear wheel torque would still be about the same (about 840 at the rear wheel in 5th at 3500 rpm compared to about 800 lbs ft with the S2 in 3rd) and therefore you should get similar acceleration to the S2 to start with and then still get an increasing acceleration all the way out of a long unwinding corner – to your top speed - without changing gear – such is the advantage of a torquey engine.
Someone described their 3.2 litre turbo as 4th gear feeling more like 2nd in a standard turbo – so I have looked at that too to see if the figures and calculations support that feeling.
The standard turbo in 2nd has an average rear wheel torque of about 1500 lbs ft whereas a 3.2 turbo with an average 400 lbs ft engine torque in 4th would produce 1400 lbs ft at the rear wheel (only 6.5% lower) and therefore very similar acceleration – yes it would feel almost as quick in 4th.
By comparison our engine would be about an average of about 1100 lbs feet in 4th so not as quick although it should be as quick in 3rd as a std car in second (producing an average of 1420 lbs ft in third) and we will test this out.
Now the argument about flat torque curves.
If theoretically there was a completely flat torque curve - then since power is torque * a constant * revs – the power would increase as a straight line with revs – i.e. would be double at double the revs. If you deviate from that straight torque curve to increase the torque at the top end – this will make that part of the graph steeper. And if as a consequence of trying to increase the torque at the top end you lose some of it lower down (which is always my experience) then that earlier part of the power graph will be lower and therefore also be steeper – so the change to a more top end power curve reveals a steeper power curve. In contrast if you change the engine so that it achieves more power at lower revs it can only do this if the torque is greater at those lower revs (so the point on the torque graph is higher) and if this has the inevitable consequence of reducing the power a bit at the top end then the torque at that top end of that graph will be lower. So the net result on the graph is a flatter graph.
So in general a steeper power graph will indicate a peaky engine whereas a flatter power graph will indicate a flatter torque curve.
Of course if you take an engine and somehow manage to increase the top end power without losing anything at the bottom – then in this case a steeper power curve will indicate a more powerful car and there will be more average torque – but practically – if you know how to do that – you are a very cleverer man. Similarly - if - as suggested you increse thw whole of the flat torque curve throughout the whole range then yes the resulting power curve would be steeper. But this seems to me to encapsulate the difficulty between theory and practice because in practice it seems almost impossible to increase the whole of the torque curve over the whole range by the same proportions everywhere. So while I must agree that in theory that is possible, to say in practice that a steeper power curve indicates more mid range or average torque is practically impossible and therefore could be misleading.
Zarcop – If we manage to fit the liners OK in a 2.5 engine then I think you could use a standard 2.5 head (with some modification) without too much detriment.
Finally, this whole exercise and the comments and replies has shown me that while many understand some if the issues, some do not still understand the important ones and even fewer have tried things to find out for themselves what is important and what is not.
Those that have eventually realise how to approach the improvement of an engine, firstly to establish what you want from it, secondly where you want it to perform (what top speed – what minimum speed, how many gears etc) and then after all that you can start to think about the best way to improve the acceleration while maintaining driveability (if that is also important).
More gears within the range of use will increase the average torque at the rear wheels and as long as the improvement in torque reduces the acceleration time more than the extra gear change time – then it is always worthwhile.
As tyres, suspension and engines have improved over the years – circuits have effectively become shorter and therefore more of an acceleration test than a top speed one and hence the ability to accelerate quickly - with control - using the relatively few gears you are stuck with (and therefore with relatively more wide ratios than are preferable for racing) makes the best choice of engine characteristics quite different to the purely theoretical route of more revs and peak bhp.
This exercise of ours is just a modest example of putting together a lot of these requirements, the coincidence of various parts from different engines fitting together quite easily and creating a whole new engine – that theoretically satisfies those requirements and then building it to test out the results.
Those who have built bigger and much faster 944 turbo engines and who have used new technology with variable vane turbos etc, etc and special fuels etc , developed new exhausts and waste gates etc etc have done much more work and with excellent results and are deserving of much more respect for it than us.
But most enthusiasts do not always have the resources to build or develop such incredible machines and we just thought that the results we got rather quickly and relatively easily and inexpensively (by comparison) were worth reporting on – so others may be encouraged to try something similar and out of it has come a commitment to manufacture a range of liners to potentially keep older engines with problems running or enable this conversion (or something similar) to be built by others.
I am sorry if in defending my teams work – I have disagreed with others and exposed their shortcomings – and I am even more sorry that this makes me seem a clever ba***rd – as I am quite happy to remain with comparative anonymity and get on with the work I enjoy here. It just seems to me that when these issues crop up with people obviously really interested in the whole technology of engine development and tuning and get so many basics wrong or misunderstand their relevance, and that when I can see their mistake, why they made it and how it will handicap their own understanding – that this is a part of the decline in our UK engineering and manufacturing in general and it is such a lot of wasted brain power that it would be helpful to them if I pointed out where I think they are going wrong and why.
Baz
Firstly – look – torque is simply a force – a twisting force – it has no connection with speed or time unless you decide to use it in a formula to create another measurement system using it. Like if you use a few constants and speed to create a reading for power or use some differences in speed to calculate acceleration.
Just because after doing that you can then reverse the formula to work backwards does not mean that when asked what torque is you could say it is something that you get when you have power or acceleration and apply mathematics or calculus to it – it is the other way around – it is the force that results in that power or that acceleration and unless you see it for what it is you will always get muddled thinking about how to use or change it for the best.
I still think the best analogy it to imagine removing the engine and fitting one of those torque spanners that bend against a scale to the prop shaft and then you sit in the engine bay and twist the torque spanner while someone with a fast shutter speed camera, photographs the torque reading on the torque spanner.
If you do not apply enough torque the car will not move – so no work is done, there is no power to calculate and no speed is achieved.
Once you apply more torque the car starts moving, work is done and at any speed you can calculate a figure to compare it to other cars (called power) to establish why some cars in this set up travel faster or further than others.
When you cannot turn the spanner with enough power to accelerate the car – the resistance to motion has equalled the torque applied (i.e. top speed).
When the torque applied is greater than the amount needed to keep the car travelling at a constant speed then the spare extra torque speeds up the rotational speed of the spanner and with it of the car – which is then accelerating (i.e. the rate of change of speed).
A more powerful person may be able to twist the spanner with more force and as a result it will accelerate quicker (as will the car) but this doesn’t mean that the twist he applies is a mathematical figure derived from the power or rate of acceleration – the twist he applies depends on the strength in his arm! Or even the tension in his muscles – just as the pressure acting on the area of the piston through the angle and radius of the con-rod does in an engine.
How much it accelerates depends upon how much extra torque is applied and as T=I*a (or acceleration = Torque/resistance), the more torque you apply the more acceleration results.
However in the above scenario – if we changed up a gear the car would accelerate more slowly because it is the rear wheel torque that accelerates it not the gearbox input torque (or engine torque). It is of course still proportional and anywhere the engine produces more torque it also produces more torque and power at the rear wheel in some proportion – but still the amount available to accelerate the car is increased or reduced by the gear ratio and final drive ratio in use.
So if an overall combined internal and final drive ratio is 2 to one say – the rear wheel torque in that gear will be twice the engine torque at any particular engine or rear wheel speed in that gear (if in this discussion we ignore internal losses as the same for each model or tuning scenario).
Fitting an S2 crown wheel and pinion shaft to a turbo gearbox (or just using the S2 gearbox) improves the rear wheel torque in any gear and at any revs by about 12.5% - so if you don’t need to travel at the original top speeds – is a good move (as the LSD can still be fitted) although it is not as strong a tooth profile and will fail sooner (which is irrelevant for racing I suppose).
However in our particular scenario – because we produce much more torque at lower revs – while a lower overall gear ratio would still improve the torque we have by 12.5% - we already have something like 75% more torque anyway – so it is not so relevant.
Indeed if you compare an S2 with our Turbo – say both changing gear from 3rd to 4th (at around 87 to 93mph) the S2 picks up at about 200 lbs ft torque and our turbo at about 340 lbs ft (engine torque) or 800 lbs ft at the wheel with the S2 or 1186 lbs ft with the turbo).
Similarly if you changed from 4th to 5th at 115mph in the S2 or 127mph in the turbo you would pick up at 200 lbs ft (engine torque 761 lbs ft rear wheel torque) in the S2 and 325lbs ft engine torque (1134 lbs ft rear wheel torque in the turbo.
This is an interesting comparison because if you went from 3rd to 4th to 5th in the S2 but missed out 4th all together in our turbo and went from 3rd straight to 5th (dropping to 3500 rpm) you would also pick up at 300 lbs ft (engine torque), the rear wheel torque would still be about the same (about 840 at the rear wheel in 5th at 3500 rpm compared to about 800 lbs ft with the S2 in 3rd) and therefore you should get similar acceleration to the S2 to start with and then still get an increasing acceleration all the way out of a long unwinding corner – to your top speed - without changing gear – such is the advantage of a torquey engine.
Someone described their 3.2 litre turbo as 4th gear feeling more like 2nd in a standard turbo – so I have looked at that too to see if the figures and calculations support that feeling.
The standard turbo in 2nd has an average rear wheel torque of about 1500 lbs ft whereas a 3.2 turbo with an average 400 lbs ft engine torque in 4th would produce 1400 lbs ft at the rear wheel (only 6.5% lower) and therefore very similar acceleration – yes it would feel almost as quick in 4th.
By comparison our engine would be about an average of about 1100 lbs feet in 4th so not as quick although it should be as quick in 3rd as a std car in second (producing an average of 1420 lbs ft in third) and we will test this out.
Now the argument about flat torque curves.
If theoretically there was a completely flat torque curve - then since power is torque * a constant * revs – the power would increase as a straight line with revs – i.e. would be double at double the revs. If you deviate from that straight torque curve to increase the torque at the top end – this will make that part of the graph steeper. And if as a consequence of trying to increase the torque at the top end you lose some of it lower down (which is always my experience) then that earlier part of the power graph will be lower and therefore also be steeper – so the change to a more top end power curve reveals a steeper power curve. In contrast if you change the engine so that it achieves more power at lower revs it can only do this if the torque is greater at those lower revs (so the point on the torque graph is higher) and if this has the inevitable consequence of reducing the power a bit at the top end then the torque at that top end of that graph will be lower. So the net result on the graph is a flatter graph.
So in general a steeper power graph will indicate a peaky engine whereas a flatter power graph will indicate a flatter torque curve.
Of course if you take an engine and somehow manage to increase the top end power without losing anything at the bottom – then in this case a steeper power curve will indicate a more powerful car and there will be more average torque – but practically – if you know how to do that – you are a very cleverer man. Similarly - if - as suggested you increse thw whole of the flat torque curve throughout the whole range then yes the resulting power curve would be steeper. But this seems to me to encapsulate the difficulty between theory and practice because in practice it seems almost impossible to increase the whole of the torque curve over the whole range by the same proportions everywhere. So while I must agree that in theory that is possible, to say in practice that a steeper power curve indicates more mid range or average torque is practically impossible and therefore could be misleading.
Zarcop – If we manage to fit the liners OK in a 2.5 engine then I think you could use a standard 2.5 head (with some modification) without too much detriment.
Finally, this whole exercise and the comments and replies has shown me that while many understand some if the issues, some do not still understand the important ones and even fewer have tried things to find out for themselves what is important and what is not.
Those that have eventually realise how to approach the improvement of an engine, firstly to establish what you want from it, secondly where you want it to perform (what top speed – what minimum speed, how many gears etc) and then after all that you can start to think about the best way to improve the acceleration while maintaining driveability (if that is also important).
More gears within the range of use will increase the average torque at the rear wheels and as long as the improvement in torque reduces the acceleration time more than the extra gear change time – then it is always worthwhile.
As tyres, suspension and engines have improved over the years – circuits have effectively become shorter and therefore more of an acceleration test than a top speed one and hence the ability to accelerate quickly - with control - using the relatively few gears you are stuck with (and therefore with relatively more wide ratios than are preferable for racing) makes the best choice of engine characteristics quite different to the purely theoretical route of more revs and peak bhp.
This exercise of ours is just a modest example of putting together a lot of these requirements, the coincidence of various parts from different engines fitting together quite easily and creating a whole new engine – that theoretically satisfies those requirements and then building it to test out the results.
Those who have built bigger and much faster 944 turbo engines and who have used new technology with variable vane turbos etc, etc and special fuels etc , developed new exhausts and waste gates etc etc have done much more work and with excellent results and are deserving of much more respect for it than us.
But most enthusiasts do not always have the resources to build or develop such incredible machines and we just thought that the results we got rather quickly and relatively easily and inexpensively (by comparison) were worth reporting on – so others may be encouraged to try something similar and out of it has come a commitment to manufacture a range of liners to potentially keep older engines with problems running or enable this conversion (or something similar) to be built by others.
I am sorry if in defending my teams work – I have disagreed with others and exposed their shortcomings – and I am even more sorry that this makes me seem a clever ba***rd – as I am quite happy to remain with comparative anonymity and get on with the work I enjoy here. It just seems to me that when these issues crop up with people obviously really interested in the whole technology of engine development and tuning and get so many basics wrong or misunderstand their relevance, and that when I can see their mistake, why they made it and how it will handicap their own understanding – that this is a part of the decline in our UK engineering and manufacturing in general and it is such a lot of wasted brain power that it would be helpful to them if I pointed out where I think they are going wrong and why.
Baz
Baz, I am a bit mystified as I haven't seen too many on here objecting to what you're saying yet you keep mentioning it as if every 2nd post, someone is taking potshots at your theories. I certainly hope you don't think I'm disagreeing. I appreciate all the time and effort you take on your replies and moreso on your website. Very comprehensive write ups. Thanks.
Personally I see your build as fitting in very nicely to a niche that most of us would find applicable for our budget restraints. In many ways I wish I'd stumbled across something like this a few years ago when I started down my very slippery slope and which I'm not at the bottom of yet either. I am very close to having my build finished and it will be something else, but I will continue to read about your builds with interest and hope to see the incoming test results.
Personally I see your build as fitting in very nicely to a niche that most of us would find applicable for our budget restraints. In many ways I wish I'd stumbled across something like this a few years ago when I started down my very slippery slope and which I'm not at the bottom of yet either. I am very close to having my build finished and it will be something else, but I will continue to read about your builds with interest and hope to see the incoming test results.
Edited by 333pg333 on Tuesday 10th November 11:41
Baz, having used your team to fully service (Gold plus, I think!) and inspect my '91 944T after i had just bought it, I echo the praise on here for your work and superbly detailed yet logical explanations of the key points.
Please keep on supplying us with your engineering insight!
Thanks again
Please keep on supplying us with your engineering insight!
Thanks again
If I seem a tad defensive it may be because I also receive private E-mails and telephone calls about my postings as well (arguing or telling me to do things differently) and they influence my replies - or it may be that I am getting too much like Victor Meldew or even that I pick up on more small mistakes people make in their replies and questions and it irks me that they are wondering about a technical issue while having a misconception about a basic rule and I just want to help put them right and stop them wasting time on a false premise.
Either way thanks so much for the positive comments and I will try and be more positive in future.
Baz
Either way thanks so much for the positive comments and I will try and be more positive in future.
Baz
Gassing Station | Porsche General | Top of Page | What's New | My Stuff