Light flywheel: Worth it?

[PeterBurgess]

Evoluzione said,”My main question is this: Has anyone ever measured the effects?”
I replied Yes.
We are not talking working it out in theory we are talking taking a measurement of the change. The inertia dyno will record the change. It is repeatable and therefore reliable. Therefore it is measurement. It is measuring the effect of changing the weight of the flywheel is it not? It is showing more energy is available to turn the road wheels rather than turn the flywheel.

Do you run dynos?

Peter

[reggid]

PeterBurgess said:

Evoluzione said,”My main question is this: Has anyone ever measured the effects?”
I replied Yes.
We are not talking working it out in theory we are talking taking a measurement of the change. The inertia dyno will record the change. It is repeatable and therefore reliable. Therefore it is measurement. It is measuring the effect of changing the weight of the flywheel is it not? It is showing more energy is available to turn the road wheels rather than turn the flywheel.

Do you run dynos?

Peter

you are indeed measuring an effect, but not necessarily the true effect of the change, for reasons that i indicated earlier. Just because the dyno gives a number even if repeatable does not make it correct....i dont need to be a regular operator to know this.

if the dyno can apply a variable load to simulate closely the acceleration rate of the real car in a given gear based on input various parameters specific to the car then the numbers might mean something. i believe some dyno software can do this but most dont and it is unlikely to be an inertia dyno that can

[PeterBurgess]

My Dynocom is built as a dual dyno system. We can use inertia testing (most real world to me) Eddy brake testing (old fashioned to my reckoning) or a combination of the two (needed to spool up turbos and make 300 + bhp cars run sweetly we tend to add 1% or 2% load which is 7.5 or 15 bhp as the eddy brake is 750). I thought most dynos have been built inertia/eddy for some years?

The problem with eddy brakes is they alter calibration as soon as they warm up so we cannot do tests as repeatable as with inertia dyno testing alone when changing a plug gap shows a difference. You need to spend time on an inertia testing dyno to see what you can achieve.

Going back to the flywheel lightening. If one lightens the flywheel the car will accelerate faster, in like for like testing, fact. Run the car before and after on an inertia dyno and you will measure the effect in terms of faster acceleration. This is achieved as more horsepower is available for acceleration n'est ce pas? More horsepower for acceleration shows up as more bhp. As I said it is displaying potential. At hillclimbs where the 60ft or 100ft times are measured when standard cars are running, it shows up when some naughty person is using an illegally lightened flywheel....same effect as inertia dyno....car accelerates faster. The engine is not making more power ( eddy dyno holding loads) but has the effect of allowing more of the power to pass to the rear wheels (inertia testing). Now one has to ask oneself interms of dyno testing, do I drive whereby I hold wot at 2000 then 3000 then 4000 in steps or do I put my foot down and accelerate or brake or cruise or sit still in traffic jams? Which dyno system is most like real world use?

Two and a half years on and we are making all our cars go faster and generally run better whether race or road. This is from using the inertia dyno.

I am sorry if this upsets those who like to calculate things to many decimal places and proove black is white, but I still inhabit a world where I still get excited and say.....ahh, but look at it wheelspin in a straightline, cos that is what increasing power is all about to us pistonheads....bringing a smile to the owners face

Peter

Edited by PeterBurgess on Friday 14th December 07:10

[stevieturbo]

Wheelspin doesn't make a car go faster. And strictly speaking, yes time is spent at various static rpm's. It may not be a long time, but it still happens.
And 60fts are largely traction defined, unless its a very low powered car. On a hillclimb or airfield I've only seen a select few go sub 2s, whether its a pilbeam on huge slicks, or a saloon car double or treble its weight ( 2wd )
In fact the fastest 60ft I've seen for a rwd car under such circumstances, was an automatic AMG Mercedes. No light flywheel there lol, or fancy tyres either.

[reggid]

PeterBurgess said:

My Dynocom is built as a dual dyno system. We can use inertia testing (most real world to me) Eddy brake testing (old fashioned to my reckoning) or a combination of the two (needed to spool up turbos and make 300 + bhp cars run sweetly we tend to add 1% or 2% load which is 7.5 or 15 bhp as the eddy brake is 750). I thought most dynos have been built inertia/eddy for some years?

The problem with eddy brakes is they alter calibration as soon as they warm up so we cannot do tests as repeatable as with inertia dyno testing alone when changing a plug gap shows a difference. You need to spend time on an inertia testing dyno to see what you can achieve.

Going back to the flywheel lightening. If one lightens the flywheel the car will accelerate faster, in like for like testing, fact. Run the car before and after on an inertia dyno and you will measure the effect in terms of faster acceleration. This is achieved as more horsepower is available for acceleration n'est ce pas? More horsepower for acceleration shows up as more bhp. As I said it is displaying potential. At hillclimbs where the 60ft or 100ft times are measured when standard cars are running, it shows up when some naughty person is using an illegally lightened flywheel....same effect as inertia dyno....car accelerates faster. The engine is not making more power ( eddy dyno holding loads) but has the effect of allowing more of the power to pass to the rear wheels (inertia testing). Now one has to ask oneself interms of dyno testing, do I drive whereby I hold wot at 2000 then 3000 then 4000 in steps or do I put my foot down and accelerate or brake or cruise or sit still in traffic jams? Which dyno system is most like real world use?

Two and a half years on and we are making all our cars go faster and generally run better whether race or road. This is from using the inertia dyno.

I am sorry if this upsets those who like to calculate things to many decimal places and proove black is white, but I still inhabit a world where I still get excited and say.....ahh, but look at it wheelspin in a straightline, cos that is what increasing power is all about to us pistonheads....bringing a smile to the owners face

Peter

Edited by PeterBurgess on Friday 14th December 07:10

Those that use a eddy current dyno (e.g. dyno dynamics) test WOT power at a specific ramp rate sweeping from say 2500 to redline. The dyno can hold at constant speed or the ramp rate can be adjusted, it is almost like a quasi adjustable inertia, none of this holding at fixed rpm business you keep mentioning ( in this part of the world for WOT power runs always a ramp rate sweep is used to avoid stuff overheating). Holding at fixed rpm is limited for light load tuning (occasionally very low rpm WOT can be used which is logical up a hill in topgear you may not accelerate at all under WOT if the gradient is steep enough) funnily enough a road car cruises at constant speed for long periods of time making holding the engine at constant rpm a worthwhile thing to be able to do and is far superior to an inertia alone system for tuning.

We have already established that a flywheel will make a car/engine accelerate faster and even generate more hp on the dyno when the rpms are not held constant for measurement. The question is whether the magnitude the machine spits out is correct that is my point. The dynos I have had done to my car the ramp rate is fixed for recorded power runs but you can alter the ramp rate (rpm/sec) and allow changes to inertia to produce a myriad of results. This in my mind make dyno testing inertia changes a misleading exercise as output increase depends on the absolute inertia of a inertia dyno and the ramp rate on a eddy current dyno.

[stevesingo]

PeterBurgess said:

The problem with eddy brakes is they alter calibration as soon as they warm up so we cannot do tests as repeatable as with inertia dyno testing alone when changing a plug gap shows a difference. You need to spend time on an inertia testing dyno to see what you can achieve.

Perhaps what your eddy brake is missing is closed loop control of the brake via a temperature compensated load cell.

I would agree that inertia testing does give repeatable results as it is basically un-fudgable, but the results are not definitively quantifiable. In a back to back test they work great, but inertia dyno does not measure the power an engine is producing, it only measures the power available for driving the wheels and there are variables that effect the available power at the wheels which are fundamentally drive train losses and ramp rate.

Drivetrain losses cannot be kept constant as changes in gearbox/diff oil temps will influence power available. Tyre pressures will influence power available and how the car is strapped down will affect the power available. Sure, this is the same for all dynos and operator diligence can keep these factors in check to a reasonable degree, although I’ve yet to see an operator monitor gearbox temps and tyre pressures whist conducting testing. A hub dyno eliminates the largest variable in the tyres.

Ramp rate cannot be controlled on an inertia dyno; that is a constant ramp rate throughout the testing rpm range. If you have an engine which makes 100lb/ft at 2000rpm and accelerates the rollers at 300rpm/sec at that point, which then goes on to produce 200lb/ft at 4000rpm, the ramp rate is now 600rpm/sec. Ok we know that the power remaining to accelerate the rollers is as exactly as stated. But what does the engine make. Unless we know the inertia value of the engine and drivetrain we will never know. Ok, a coast down can “measure” the additional inertia of the drivetrain up until the gearbox. The inertia of the input shaft, clutch disc, and engine mass is still unknown. That unknown inertia is absorbing power throughout, and the amount of power the unknown inertia absorbs is changing with ramp rate which is not constant.

On some eddy dynos, you can mitigate the effect of drivetrain inertia by performing a static test in the middle of the rev range. Let’s say we do a 3000rpm static test and get 200bhp. We then do a dynamic test at a fixed ramp rate and compare the 3000rpm power to the power made during the static test. If it is higher during the dynamic test, then the inertia value inputted in to the software is too high. i.e. the software thinks the engine is accelerating a higher inertia that it actually is. This value is edited so that the dynamic test matches the static test. This is compensating for the whole engine/drivetrain/wheel inertia.

I am not putting down inertia dynos. In fact I used a inertia dyno recently to verify my engine against a similar engine as poor operation of an eddy current dyno lead me to believe that either I had an issue of the dyno operation was wrong.

A lightweight flywheel does not make the engine produce more power, it just removes a burdon from the engine so the engines efforts can be better used elsewhere.

[reggid]

stevesingo said:

A lightweight flywheel does not make the engine produce more power, it just removes a burdon from the engine so the engines efforts can be better used elsewhere.

by that analogy anything that reduces friction does not increase the power? i understand what you mean though.

yeah if it doesn't increase the Hp under both fixed rpm test and sweep test it aint a real HP improvement IMO.

The way to describe it might be that the IMEP does not change.......basically cylinder pressures dont change

[stevesingo]

Ok, perhaps I should have said "removes an inertial burdon". Personally, I would consider reduction in engine friction a power increaser. IEMP can remain the same but you can get more power.

[PeterBurgess]

Do you remember Oddball from Kelly's Heroes? Well I am like Oddball and don't know how they work, I just drive the things

I can say the electronics stuff is not as robust as my old purely mechanical water brake(that is thye penalty one has to pay with electronic stuff!), but the information and speed of data aquisition is stunning. The difference between going on a dyno now and again and running and maintaining one is one sees it warts and all and learns how to keep the system tip top, at the end of the day it is a workshop tool not a scientific instrument.

I attach a copy and paste from Dynocoms website about the system I bought from them. I am sure Paul who designs/develops and builds the dynos will be more than happy to tell you all the ins and outs.

This thread started off....can anyone measure the effect and again I say yes I can.

Peter

5000 Series
$ 20,995 includes load!
The 5000 series is the world's most affordable chassis dynamometer. But don't let its price fool you; the 5000 Series dynamometer is capable of supporting speeds up to 175+ MPH and 5000+ ft lbs of torque. The maximum axle weight is 6,500 lbs and the track width range is 36"-86". The 5000 was designed for a variety of different testing scenarios – FWD/RWD Cars, Sport Compacts, Diesel Trucks, Motorcycles and ATV’s. With the stainless steel coverings and zinc plated knurled rollers this dyno is equipped to handle all of your companies needs. Ideal for portability when equipped with the caster/dolly kit. It is equipped with a FRENESLA eddy brake and you are able to perform acceleration, step, sweep and steady-state tests. • View in real-time torque/horsepower output, at steady and changing speeds, to instantly evaluate changes you've made to the engine's fuel or timing maps. • Diagnose engine and drivetrain problems. • Troubleshoot drivability issues. • Run track ¼ mile or circle track lap simulations with reaction times that you determine in the software parameters. • Bi-Directional roller for testing of both RWD and FWD vehicles. The 5000 Series is fully upgradeable in the field, it can be coupled with any other Dynocom Chassis Dynamometer (7500, 15,000, or DC POD’s) for All-Wheel-Drive Testing.

[Pumaracing]

Lol. Now you can all see why I said on page one I wasn't going to get sucked into arguing about this topic. Two and half more pages of the same thing being said over and over but using slightly different words. None of which make an inertia reduction the same thing as a genuine horsepower increase as it seems most people understand very well.

Only the steady state horsepower curve allows one to calculate how fast a vehicle will accelerate and what top speed it will have. Any other numbers distort the calculations. At top speed all of an engine's bhp is being absorbed into overcoming air and rolling resistance and is of course a steady state condition in its own right. No amount of inertia reduction will change this top speed one iota, it will just alter how fast the vehicle gets there. Only a steady state bhp change will alter top speed for a given vehicle.

So clearly to fully describe or model an engine's performance it is necessary to know both the steady state bhp curve plus the inertia factors which is why I include both in my simulation program. Less inertia is obviously a good thing but to try and describe that inertia reduction as a bhp increase is neither logically nor mathematically correct and especially as that bhp increase figure will vary in each gear or with any change in gearing.

Anyway enough already. Cue more pointless bickering.

[MFaulks]

Lol... It is good fun though David :-). I think we can all get a bit too precious about our own particular view point, trying to hammer our own version of the flat world, and miss the humour that a lot of this contains if you look back over it. At the end of the day, much comes down to what you are doing and assuming we are talking racing of some sort, from salt flat where hp is king, to short track events with lots of transient engine rpm changes being demanded, then the appropriate view point will change. I totally agree the key behind all of this is repeatability of the test, and the instrumentation, and making sure you are actually measuring what you think you are, but that as in all life comes down to the competence of the engineer / technician, no spreadsheet can ever control that, nor would we want it at the end of the day, or we could all be replaced and life would be rather dull... And also establishing a repeatable A-B-A baseline. To Peter's point on his dyno, he has the capability to run it as a pure inertial, or an inertial with a steady state load applied. I believe the better inertial setups all have that, so the inertial / non-inertial argument is a mute point. Design your experiment / test, and then analyse your results on the basis of the limitations of your experiment, but as suggested, put it to the practical test and see where you are against your competition given this is the final measurement. Obviously all the parasitics need to be considered in the true world, but reduce any one of them as it applies to what you are doing, and you should be making positive progress however small that may be. If you have a look at the technical data on Sachs performance clutch baskets, you will see their business is based on making these as light as possible. If there was no need or call for it at the high end they would have changed their business model - dollars talk.

[Pumaracing]

How are you getting on with your flow bench Martin?

[andygtt]

I have been mulling this over...

Will a light flywheel have more effect on a high power car than a low power car?

Why?... well the light flywheel helps acceleration of the engine right, but not power.... however high power cars are always on the search for traction... loss of traction equates to fast rise in revs as wheelspin starts, then a sudden drop in revs when the traction returns!

So does a light flywheel make a high power car easier to control on the edge of traction and thus more progressive and faster?

[PeterBurgess]

Dave, as I understand it from your last post you mean you are going to purchase an engine dyno, hub dyno and rolling road dyno so you can get some accurate figures with which to augment your simulation? Maybe a wind tunnel to measure drag too?

Peter

[Pumaracing]

PeterBurgess said:

Dave, as I understand it from your last post you mean you are going to purchase an engine dyno, hub dyno and rolling road dyno so you can get some accurate figures with which to augment your simulation? Maybe a wind tunnel to measure drag too?

Peter

Peter, your wild extrapolations and straw man arguments from what people have actually said into absurd generalisations and suppositions that they haven't even mentioned are starting to make you look foolish. Now I know you aren't one of the most benightedly unintelligent life forms it's been my profound lack of displeasure to fail to have ever avoided meeting but you do love to bicker, you do think that having a degree in psychology gives you some sort of ability to tie people into knots with logical or tautological arguments but that only works with the hard of thinking and I'm very far from one of those.

You might be well advised to quit while you're not as far behind as you might end up if you continue with this.

I trust however you appreciate the HHGTTG reference

I suggest you suck on the red corner of your towel for a bit. It contains mood stabilisers and benzodiazepines that will make you feel very cool and froody for a while.

[PeterBurgess]

Stevesingo said ,”Ok, perhaps I should have said "removes an inertial burdon". Personally, I would consider reduction in engine friction a power increaser. IEMP can remain the same but you can get more power”

We spent a session recently with a customer who had changed oils in engine,box and diff from olde worlde stuff to modern state of the art oils. I pointed out we had some very low oil pressures recorded with thin oils when hot in older engines with large volume oil galleries, so low that warning lights/buzzers were on. He said not racing so should be ok.

The rear wheel power went up by 4 bhp, approx 5% increase in rwp over previuos session. The coast down test showed the losses had reduced so we still had the same 'flywheel' power as before, just more power hitting the back wheels.

In subsequent road use the customer hit some bad traffic jams and the oil pressure went to almost nothing so he has gone back to semi-gloop oil.


The ineresting thing to me is selection of oils for competition, as thin as possible for drag racing as the runs are so short it would be difficult to kill engine, box or diff/axle. I know Silkolene/Fuchs run oil in their circuit race bikes which lasts just long enough for one race, absolutely minimum viscosity.


Dave


Peter

[reggid]

i think the validity of coastdown losses should be saved for a thread of its own......

[PeterBurgess]

I for one would not join in an argument about validity of coastdown tests/inertia dyno accuracy or whatever. I post on the threads to share with PHers the information and knowledge we gain from our work, as long as results are repeatable we gain knowledge and move forwards. I need to do this as we still work hard in the race world and I want our engines/heads/rolling road tuning to work as best it can. The results speak for themselves year on year. It would seem with like for like drivers and if all else is equal then the car/bike with the most bhp at the wheels is most likely to win, we are happy to use all the tools we have to try and achieve this.

Peter

[andygtt]

lets not forget a dyno is just a tool to establish one factor of performance which JUST measures power... and unless physics have just left the room, imo any dyno recording a 'bhp' increase for lightening a flywheel is clearly not measuring correctly and is surly just showing how variances can make it inaccurate?
Because Im pretty sure physics says BHP is a measurement of torque as a formula of the RPM its recorded at?.... and lightening a flywheel cant have any effect on these?

I can guarentee I can measure the effect of my lightened flywheel FAR more repeatable and accuratly..... I know how much it exactly cost and therefore the effect on my wallet... its FACT and REPEATABLE.... but meaningless in the context of my car going faster, but an important factor if i choose to miss-read the OP!!!

Like the OP I was actually interested in getting some useful discussion about whether a lightened flywheel is genuinely worth is and if anyone had actually got some measurable increases in performance from using one.... IMO by performance the OP was clearly asking for real worth car going faster 'performance'... Id take meaningful calculations over missleading dyno readings... but then i'm not the OP.

[DVandrews]

It's simple, lightening the flywheel is effectively lightening the car, before accelerating the vehicle the engine first has to accelerate itself, reduce the inertial loading of the engine and you improve acceleration of the whole kaboodle , the effect is felt more in the lower gears where the inertial load of the flywheel is greater as a percentage of the overall inertail load of the vehicle when the gearing is taken into account.

There is no increase in power or torque, it's simply that the engine has less work to do.

There are some negatives, an increased risk of stalling on pull-away and a more rapid nose dive of RPM between gear changes. Subjectively the engine feels more responsive.

Dave

Edited by DVandrews on Sunday 16th December 11:21