3/5/7 angle valve jobs?
Discussion
varnish5000 said:
Something I've heard mentioned but again have not found any literature on is pressure recovery.
Ah, pressure recovery. The bane of my damn life. I've made a complete arse of myself posting about that in the past as well as two emails last week to DV accusing him of getting things wrong in his new book which I've now finally realised he was right on all along and I was wrong. So this will save an email by putting it in public. I was wrong and clearly my brain is not working properly anymore which I will try and blame on booze, fags and old age.After a flow restriction pressure recovery can occur if the flow area increases gradually. For a venturi tube the general consensus is a divergent cone of between 7 and 15 degrees included angle after the throat. So in cylinder heads and on valve seats if we can duplicate that we can achieve some pressure recovery and increase the flow figures at a given pressure drop across the restriction.
This might indicate that the top cut on an inlet seat needs to be closer to the valve seat angle than previously thought. Perhaps 38 degrees for a 45 degree seat rather than a 30 degree topcut.
On an exhaust seat it might indicate that going straight to a 70 degree bottom cut after a 45 degree seat is wrong. That a shallower bottom cut, or a radius, will work better and that the backcut on the valve might need to be at 38 degrees rather than 30.
So DV just ignore my last two emails. You can call me a tw*t if you like next time we speak.
varnish5000 said:
I always thought the reason they had different port volumes was for different engine capacities.
I actually think this is perhaps a purely American concept because I can't recall port volume (or area) vs engine capacity ever even being mentioned over here and it's not something I've ever felt the slightest need to consider.Certainly we also have plenty of engines of considerably different capacities that take the same cylinder head such as the Ford Pinto, Crossflow, various VWs, Peugeot XU etc but I don't think anyone would change the port size just because of engine capacity nor can I see any reason to.
IMO you set your port size to match what the valve can potentially flow at the cam lift being used. Clearly it's irrelevant what the valve flows at higher lift than this because it's never going to get there. So I set myself a flow target for each head based on how downdraft it is and other factors and from that I can calculate the port size needed. The flow bench is the final arbiter but the engine size never factors into it.
So has the entire American tuning industry got it wrong? Are factors being attributed to changes in port volume actually being caused only by the extra airflow the bigger ports generate? Time for DV to chip in again methinks.
I'd like to see that article I linked to being run again in a different way. Take four heads and modify them for extra airflow in equal steps by only increasing the port size as much as necessary to gain the desired flow increase. Done properly the flow increase and port area increase should stay very much pro rata. I predict the peak power will still go up in proportion to flow but the loss of bottom end torque will be nothing like that which resulted from huge ports with little extra flow.
Pumaracing said:
Ah, pressure recovery. The bane of my damn life.
After a flow restriction pressure recovery can occur if the flow area increases gradually. For a venturi tube the general consensus is a divergent cone of between 7 and 15 degrees included angle after the throat. So in cylinder heads and on valve seats if we can duplicate that we can achieve some pressure recovery and increase the flow figures at a given pressure drop across the restriction.
This might indicate that the top cut on an inlet seat needs to be closer to the valve seat angle than previously thought. Perhaps 38 degrees for a 45 degree seat rather than a 30 degree topcut.
This might be were a 7 angle seat starts to be appropriate by blending the seat into the chamber.After a flow restriction pressure recovery can occur if the flow area increases gradually. For a venturi tube the general consensus is a divergent cone of between 7 and 15 degrees included angle after the throat. So in cylinder heads and on valve seats if we can duplicate that we can achieve some pressure recovery and increase the flow figures at a given pressure drop across the restriction.
This might indicate that the top cut on an inlet seat needs to be closer to the valve seat angle than previously thought. Perhaps 38 degrees for a 45 degree seat rather than a 30 degree topcut.
The hemi chamber with its gentle angle off the seat is great at recovering pressure, but it isn’t the best shape chamber in other respects.
How can we get the chamber of a 4V per cylinder head to perform as well?
Is it as simple as working the squish band around valve to give a gentle radius? Can we use the squish band to valve head interaction to create a variable venturi? Would this upset things, or improve flow by moving the air out of the way quicker?
Pumaracing said:
On an exhaust seat it might indicate that going straight to a 70 degree bottom cut after a 45 degree seat is wrong. That a shallower bottom cut, or a radius, will work better and that the backcut on the valve might need to be at 38 degrees rather than 30.
Is this as relevant as it is on the inlet side? The exhaust pressure is being recovered by the atmosphere, and the gasses are rapidly expanding as they leave the cylinder.Pumaracing said:
varnish5000 said:
I always thought the reason they had different port volumes was for different engine capacities.
I actually think this is perhaps a purely American concept because I can't recall port volume (or area) vs engine capacity ever even being mentioned over here and it's not something I've ever felt the slightest need to consider.IMO you set your port size to match what the valve can potentially flow at the cam lift being used. Clearly it's irrelevant what the valve flows at higher lift than this because it's never going to get there. So I set myself a flow target for each head based on how downdraft it is and other factors and from that I can calculate the port size needed. The flow bench is the final arbiter but the engine size never factors into it.
The way I have thought about developing a head is consider how much air the engine wants, which is basically a function of engine displacement and rpm.
Then see what valve size is needed to get that much air into the engine, by just applying a discharge coefficient and taking into consideration the valve stem diameter and seat width.
You can use a simple calculation to predict the flow through the curtain area. Up to the convergence point the Cd stays pretty stable, after this the coefficient drops way down, as you’d expect. Measuring the coefficient from the (seat area-stem area) you’ll see the Cd numbers are around the same at the convergence point and will continue to increase as you lift through and past it. Up to a point.
This gives an estimate of the valve lift you’ll need which is easily backed up by a flow test.
I then run a calculation to find the port diameter (area) needed to set the airspeed at maximum CFM where I want it, assuming the Cd of the port is 1.0
I’m an engineering student (I haven't got any money) so I haven’t had the chance to apply any of this to a running engine.
I’m just playing with old cylinder heads and a homemade flow bench, but its still pretty fun when the numbers from the bench match up with the predicted values.
David Vizard said:
My new cylinder head book really delves into the myths, misconceptions, underestimations and the realities of port velocity. It actually has diagrams in it that explain why even those who tell you it's important are doing little other than paying lip service to this element of cylinder head modifying. There are also dyno tests to show what happens to the type of engines you and I run (as apposed to F1) when port velocity is changed.
Book will be out late feb and in books stores hopefully by end of March.
And Dave B - please don't spill the beans on this one!!
DV
Respect to both Daves.Book will be out late feb and in books stores hopefully by end of March.
And Dave B - please don't spill the beans on this one!!
DV
How relevant will the book be to the next generation of ultra-boosted GDi engines approaching 30 bar BMEP?
Yuxi said:
Respect to both Daves.
How relevant will the book be to the next generation of ultra-boosted GDi engines approaching 30 bar BMEP?
Don't really have an answer for that but it does show the cylinder head did for Ryan Garcia's giant killing 1986 Mitsubishi Lancer. This made 1172 HP at the rear wheels (observed) on wrinkle wall slicks an a Florida summer day.How relevant will the book be to the next generation of ultra-boosted GDi engines approaching 30 bar BMEP?
How does that compare output wise with what you are talking about?
DV
Yuxi said:
How relevant will the book be to the next generation of ultra-boosted GDi engines approaching 30 bar BMEP?
The problem you will face with a modern wall or spray guided GDI engine is that the port geometry is a compromise between flow and charge motion. A huge amount of CFD is done to ensure that the intake air charge ends up in the correct location(in terms of bulk momentum/movement and localised turbulence), so that when the fuel spray is injected, the whole lot ends up in the right place to be lit by the spark and then to burn at a controlled rate and crank angle window. This is even more important during stratefied operation and during light load operation to optimise both engine out emissions and maximise fuel economy (by optimising the heat release process).If you modify the port / valves etc to increase flow (which you will be able to do) then you also run the risk of reducing the efficiency of the combustion process (and in fact, actually cause lean misfires in extremis). Because most modern GDI engine will be forced induction, then simply increasing the boost pressure is a much better solution for aftermarket tuning etc
Yuxi said:
How relevant will the book be to the next generation of ultra-boosted GDi engines approaching 30 bar BMEP?
Eventually there will be a point where boosting further is not going to be possible unless you lower the CR or you would retard and then keep on retarding. If you retard so much the otto cycle loses so much efficiency, lowering the compression ratio too much again loses alot of efficiency at part load, and goes hand in hand with more boost obviously, which can be laggier than what we're used to now with good turbo set ups. And there is also risk of burning out your exhaust valves with too much retard.With a GDI engine a home modifier will have problems getting the engine they have modified to run well if the air is in the wrong place for the fuel being injected. They may be lucky but probably won't be, they could convert over to port injection but they would then have to lower the CR which will affect performance and efficiency.
Realistically the way forward at that point is for a tuner to make a high performance version of their selected engine with a well researched combustion system using a combination of analytical and testing techniques, optimising the charge motion at the right crank angle but of course this will be very expensive.
I came across this very interesting article while perusing the intergoogles.
http://www.hotrod.com/techarticles/engine/hrdp_101...
Ten high flow modified heads tested against the stock one on a 6.8 litre LS engine with a big lift cam (620 thou). Inlet valves ranged from the 51 mm ones in the stock heads to huge 55 mm ones in a couple of the aftermarket offerings.
There's an awful lot of info in there so I scribbled the important bits down on a scrap of paper to save scrolling up and down the web page like crazy. Flow at 600 thou lift, port volume, peak power and average torque.
Most of the engines made around the 620 bhp mark. So can we see any correlation between the best and worst engines with port volume, valve size, flow or anything else? Well not very easily, at least at first. So let's look at the highest bhp engine which was test 6 with the Procomp heads and see if there's anything unusual about it. These made 629 bhp, a fair bit up on the next best heads. However at 52 mm they have the smallest valves of any modified head, the worst exhaust flow and not very high inlet flow. So why the hell do they produce the most bhp?
To answer that I typed all the info into a spreadsheet and divided peak flow by port volume to get an idea of port efficiency, or gas speed. Lo and behold the Procomps have by far the smallest ports at only 219 cc. Nearly 40 cc smaller than the biggest ports and barely larger than the stock 205 cc ports which they flow 35% more than. This extremely skillful port design gave them the highest flow / volume ratio of any heads tested at 1.47 CFM per cc.
Hmmmm. So which heads had the worst port efficiency? Test 11, the World Products heads were real stinkers. With monstrous 255 cc ports, big valves and yet the lowest flow of any modified head tested they achieved a miserable 1.23 CFM per cc. The Procomp heads have nearly 20% more flow efficiency. In fact it's hard to see how with 53.5 mm valves and such huge ports the designer managed to mill out so much port material and yet still managed to miss the bits that were restricting the valve flow. It's so inept it's almost skillful.
So how did they fare? Dead last with only 602 bhp although to be fair they also couldn't be run with high lift rockers because of another design cockup which was quoted as losing them 8 to 10 bhp - however they'd still have been dead last even if you added that back.
Which heads had the next worst flow efficiency? The Dart heads at 1.28 CFM per cc and guess what? They also came in next to last in the bhp stakes.
A message is starting to become apparent. Making ports bigger than they need to be produces poor cylinder heads. Even though this was a 600 bhp plus engine with over 90 bhp per litre the big ports just made things worse not better.
http://www.hotrod.com/techarticles/engine/hrdp_101...
Ten high flow modified heads tested against the stock one on a 6.8 litre LS engine with a big lift cam (620 thou). Inlet valves ranged from the 51 mm ones in the stock heads to huge 55 mm ones in a couple of the aftermarket offerings.
There's an awful lot of info in there so I scribbled the important bits down on a scrap of paper to save scrolling up and down the web page like crazy. Flow at 600 thou lift, port volume, peak power and average torque.
Most of the engines made around the 620 bhp mark. So can we see any correlation between the best and worst engines with port volume, valve size, flow or anything else? Well not very easily, at least at first. So let's look at the highest bhp engine which was test 6 with the Procomp heads and see if there's anything unusual about it. These made 629 bhp, a fair bit up on the next best heads. However at 52 mm they have the smallest valves of any modified head, the worst exhaust flow and not very high inlet flow. So why the hell do they produce the most bhp?
To answer that I typed all the info into a spreadsheet and divided peak flow by port volume to get an idea of port efficiency, or gas speed. Lo and behold the Procomps have by far the smallest ports at only 219 cc. Nearly 40 cc smaller than the biggest ports and barely larger than the stock 205 cc ports which they flow 35% more than. This extremely skillful port design gave them the highest flow / volume ratio of any heads tested at 1.47 CFM per cc.
Hmmmm. So which heads had the worst port efficiency? Test 11, the World Products heads were real stinkers. With monstrous 255 cc ports, big valves and yet the lowest flow of any modified head tested they achieved a miserable 1.23 CFM per cc. The Procomp heads have nearly 20% more flow efficiency. In fact it's hard to see how with 53.5 mm valves and such huge ports the designer managed to mill out so much port material and yet still managed to miss the bits that were restricting the valve flow. It's so inept it's almost skillful.
So how did they fare? Dead last with only 602 bhp although to be fair they also couldn't be run with high lift rockers because of another design cockup which was quoted as losing them 8 to 10 bhp - however they'd still have been dead last even if you added that back.
Which heads had the next worst flow efficiency? The Dart heads at 1.28 CFM per cc and guess what? They also came in next to last in the bhp stakes.
A message is starting to become apparent. Making ports bigger than they need to be produces poor cylinder heads. Even though this was a 600 bhp plus engine with over 90 bhp per litre the big ports just made things worse not better.
Edited by Pumaracing on Thursday 29th December 14:16
This is why choosing heads is such a minefield.
What information does the average punter need to know from sellers in order to make the right choice ?
And some of the US LS heads also sell different valve angles as one of their plus points. Does altering the valve angle by only 2-3deg really make that much difference ? I think the std LS is around 15 deg, TFS sell 13 deg or so and some go to 11 deg ?
Cant rem the angles off the top of my head.
What information does the average punter need to know from sellers in order to make the right choice ?
And some of the US LS heads also sell different valve angles as one of their plus points. Does altering the valve angle by only 2-3deg really make that much difference ? I think the std LS is around 15 deg, TFS sell 13 deg or so and some go to 11 deg ?
Cant rem the angles off the top of my head.
Pumaracing said:
I came across this very interesting article while perusing the intergoogles.
http://www.hotrod.com/techarticles/engine/hrdp_101...
Ten high flow modified heads tested against the stock one on a 6.8 litre LS engine with a big lift cam (620 thou). Inlet valves ranged from the 51 mm ones in the stock heads to huge 55 mm ones in a couple of the aftermarket offerings.
There's an awful lot of info in there so I scribbled the important bits down on a scrap of paper to save scrolling up and down the web page like crazy. Flow at 600 thou lift, port volume, peak power and average torque.
Most of the engines made around the 620 bhp mark. So can we see any correlation between the best and worst engines with port volume, valve size, flow or anything else? Well not very easily, at least at first. So let's look at the highest bhp engine which was test 6 with the Procomp heads and see if there's anything unusual about it. These made 629 bhp, a fair bit up on the next best heads. However at 52 mm they have the smallest valves of any modified head, the worst exhaust flow and not very high inlet flow. So why the hell do they produce the most bhp?
To answer that I typed all the info into a spreadsheet and divided peak flow by port volume to get an idea of port efficiency, or gas speed. Lo and behold the Procomps have by far the smallest ports at only 219 cc. Nearly 40 cc smaller than the biggest ports and barely larger than the stock 205 cc ports which they flow 35% more than. This extremely skillful port design gave them the highest flow / volume ratio of any heads tested at 1.47 CFM per cc.
Hmmmm. So which heads had the worst port efficiency? Test 11, the World Products heads were real stinkers. With monstrous 255 cc ports, big valves and yet the lowest flow of any modified head tested they achieved a miserable 1.23 CFM per cc. The Procomp heads have nearly 20% more flow efficiency. In fact it's hard to see how with 53.5 mm valves and such huge ports the designer managed to mill out so much port material and yet still managed to miss the bits that were restricting the valve flow. It's so inept it's almost skillful.
So how did they fare? Dead last with only 302 bhp although to be fair they also couldn't be run with high lift rockers because of another design cockup which was quoted as losing them 8 to 10 bhp - however they'd still have been dead last even if you added that back.
Which heads had the next worst flow efficiency? The Dart heads at 1.28 CFM per cc and guess what? They also came in next to last in the bhp stakes.
A message is starting to become apparent. Making ports bigger than they need to be produces poor cylinder heads. Even though this was a 600 bhp plus engine with over 90 bhp per litre the big ports just made things worse not better.
Astonishing.http://www.hotrod.com/techarticles/engine/hrdp_101...
Ten high flow modified heads tested against the stock one on a 6.8 litre LS engine with a big lift cam (620 thou). Inlet valves ranged from the 51 mm ones in the stock heads to huge 55 mm ones in a couple of the aftermarket offerings.
There's an awful lot of info in there so I scribbled the important bits down on a scrap of paper to save scrolling up and down the web page like crazy. Flow at 600 thou lift, port volume, peak power and average torque.
Most of the engines made around the 620 bhp mark. So can we see any correlation between the best and worst engines with port volume, valve size, flow or anything else? Well not very easily, at least at first. So let's look at the highest bhp engine which was test 6 with the Procomp heads and see if there's anything unusual about it. These made 629 bhp, a fair bit up on the next best heads. However at 52 mm they have the smallest valves of any modified head, the worst exhaust flow and not very high inlet flow. So why the hell do they produce the most bhp?
To answer that I typed all the info into a spreadsheet and divided peak flow by port volume to get an idea of port efficiency, or gas speed. Lo and behold the Procomps have by far the smallest ports at only 219 cc. Nearly 40 cc smaller than the biggest ports and barely larger than the stock 205 cc ports which they flow 35% more than. This extremely skillful port design gave them the highest flow / volume ratio of any heads tested at 1.47 CFM per cc.
Hmmmm. So which heads had the worst port efficiency? Test 11, the World Products heads were real stinkers. With monstrous 255 cc ports, big valves and yet the lowest flow of any modified head tested they achieved a miserable 1.23 CFM per cc. The Procomp heads have nearly 20% more flow efficiency. In fact it's hard to see how with 53.5 mm valves and such huge ports the designer managed to mill out so much port material and yet still managed to miss the bits that were restricting the valve flow. It's so inept it's almost skillful.
So how did they fare? Dead last with only 302 bhp although to be fair they also couldn't be run with high lift rockers because of another design cockup which was quoted as losing them 8 to 10 bhp - however they'd still have been dead last even if you added that back.
Which heads had the next worst flow efficiency? The Dart heads at 1.28 CFM per cc and guess what? They also came in next to last in the bhp stakes.
A message is starting to become apparent. Making ports bigger than they need to be produces poor cylinder heads. Even though this was a 600 bhp plus engine with over 90 bhp per litre the big ports just made things worse not better.
I am now going to go look for an unmodified head casting to start all over again
That is an interesting read but two things stand out for me..
CR is not always the same (cc of head) .. the one with 63cc gave the most power
and secondly the peak bhp for the most part was in the same ball park (excluding the standard head)
and is almost too close to measure but for racing it probably makes all the difference.
CR is not always the same (cc of head) .. the one with 63cc gave the most power
and secondly the peak bhp for the most part was in the same ball park (excluding the standard head)
and is almost too close to measure but for racing it probably makes all the difference.
rev-erend said:
That is an interesting read but two things stand out for me..
CR is not always the same (cc of head) .. the one with 63cc gave the most power
Seriously? You think 1 cc, the difference between 11.0 and 11.1 compression ratio (work it out) made the slightest difference to power? Other things should be standing out for you in the data presented.CR is not always the same (cc of head) .. the one with 63cc gave the most power
Okay, so the question is why are smaller ports better than bigger ports?
My answer would be higher gas velocity because;
There is less chance of reversion
More inertia cylinder filling (If this phenomenon actually exists?)
Better mixing of air and fuel leading to improved combustion.
But there is so much more to it than just how much air the head can move, and how fast it can move it.
How do we know that the pro comp heads haven't had the squish area welded up which has improved combustion, and that is what is taking up 1cc extra? Maybe all the reduction in the pro comp chamber volume is through welding, and they've improved the pressure recovery as a result.
Or has the plug has been moved to a more central position, or the ports produce more or less swirl than the others?
Its moving less air than the other heads, so it has to be utilising it more efficiently. But how?
They said all the heads liked the same ignition advance, so maybe the chambers are all the same.
My answer would be higher gas velocity because;
There is less chance of reversion
More inertia cylinder filling (If this phenomenon actually exists?)
Better mixing of air and fuel leading to improved combustion.
But there is so much more to it than just how much air the head can move, and how fast it can move it.
How do we know that the pro comp heads haven't had the squish area welded up which has improved combustion, and that is what is taking up 1cc extra? Maybe all the reduction in the pro comp chamber volume is through welding, and they've improved the pressure recovery as a result.
Or has the plug has been moved to a more central position, or the ports produce more or less swirl than the others?
Its moving less air than the other heads, so it has to be utilising it more efficiently. But how?
They said all the heads liked the same ignition advance, so maybe the chambers are all the same.
stevieturbo said:
This is why choosing heads is such a minefield.
What information does the average punter need to know from sellers in order to make the right choice ?
Well my boy. Wot choo need to do is buy my new book on engine tuning which will be rolling hot off the presses in Feb or March (not sure which year, or if I'll ever get round to writing it). In this magnificent tome I'll tell you how to design intake ports that flow at 125% efficiency with zero metal removal from stock. How to design camshafts with standard duration but 50% more than standard lift, no additional valve train forces AND they'll run on stock springs.What information does the average punter need to know from sellers in order to make the right choice ?
I'll let you into the closely guarded secrets of how machining tiny grooves into the top of your pistons will create Plasma Flow that increases power by 200% and reduces fuel consumption to almost zero.
I'll show you how to cut valve seats that conduct so much heat away from the valves that it creates cryogenic conditions inside the combustion chamber that eliminates detonation, runs on zero ignition advance, turns the sump oil into an edible product you can fry your chips in and makes you seriously attractive to young women.
It'll have an entire chapter on the Hondasaki engine I built for Rowan Egret that produced an imaginary 3200 bhp from only 1.5 litres, ran on kerosene and had zero exhaust emissions. On its first trip to the drag strip it accelerated so fast his eyes popped back into his skull cavity and his testicles climbed up into his abdomen. He covered the first 400 yards in under 3 seconds and would have smashed all known 1/4 mile drag strip records except that having just gone blind he steered off the track and into a cow field. After the race a qualified physician had to smack him upside the head to make his eyes pop back out and on the arse to make his balls drop down again.
It'll have another chapter on the same engine with more pictures and shorter words for American purchasers.
All online orders will come with a free bottle of Dr Dave's Patented Herbal Restorative and Hair Conditioner. This wondrous product cures Scrofula, ague, herpes, lethargy, acne, polio, whooping cough and baldness. Added to your petrol tank it increases octane value by 10 points and just two drops in your date's drink will make her mad with desire and willing to fulfill your every need.
Finally the first 100 signed copies will come with a towel because every intergalactic hitchhiker needs to know where his towel's at. One corner will be soaked in nutrients for when you get peckish, another in uppers for when you feel down and the third in downers for when you feel too up. The fourth corner is soaked in detergent because that's the corner you wipe your backside with. Try not to suck that corner too often.
varnish5000 said:
Okay, so the question is why are smaller ports better than bigger ports?
My answer would be higher gas velocity because;
There is less chance of reversion
More inertia cylinder filling (If this phenomenon actually exists?)
Better mixing of air and fuel leading to improved combustion.
But there is so much more to it than just how much air the head can move, and how fast it can move it.
How do we know that the pro comp heads haven't had the squish area welded up which has improved combustion, and that is what is taking up 1cc extra?
Maybe all the reduction in the pro comp chamber volume is through welding, and they've improved the pressure recovery as a result.
Struth. Why this miniscule 1cc difference which is utterly irrelevant to anything is attracting any attention at all eludes me. The magazine asked the head suppliers to all skim their heads to 64cc because that's what they needed for 11:1 CR and everyone got it right within an accuracy of 1cc or so which is nothing. No one welded anything up. All the heads are unique castings anyway except the one which was a modified standard head.My answer would be higher gas velocity because;
There is less chance of reversion
More inertia cylinder filling (If this phenomenon actually exists?)
Better mixing of air and fuel leading to improved combustion.
But there is so much more to it than just how much air the head can move, and how fast it can move it.
How do we know that the pro comp heads haven't had the squish area welded up which has improved combustion, and that is what is taking up 1cc extra?
Maybe all the reduction in the pro comp chamber volume is through welding, and they've improved the pressure recovery as a result.
varnish5000 said:
Or has the plug has been moved to a more central position, or the ports produce more or less swirl than the others?
Its moving less air than the other heads,
No, clearly it's not which is why it's producing more power. The reasons why ought to be apparent.Its moving less air than the other heads,
Two main things should be striking anyone who reads that article and does even the quickest analysis of the flow figures and the bhp ones. Maybe I'm expecting too much but part of the skill of developing good engines is being able to analyse the results you already have and understand what they are telling you.
So can anyone tell me what things stand out as being odd about that whole test session?
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