Had my ’95 M3 3.0 Dyno’d today.

The word is LOSS. That means to me I am LOOSING engine power because of transmission.
But this narrows this problem down. Looks like we have a half full or half empty glass situation here.

Horsepower are generated by the engine. What ends up on the road/wheels is what is left of it.
Everything between are the losses.

My engine produced 245bhp - 22% = 190.9bhp LEFT at the wheels.

I would be happy with the 266bhp you worked out but at least is shows that we are not that far out.

It all depends from which end you look at the problem.

lol ! Well,thats that little problem solved

Cossie wrote: working it out like that si it does work, you have approx 28% loss I think.. Mine is approx 36 / 37% loss but it's 4wd

Yep,finally sorted it thank god !! Seems to be about right for yours and mine.

I am not. I want these 317hbp

just joking

Cossie wrote: UweM3 wrote: I am not. I want these 317hbp just joking   Don't worry he didn't even get that. lol was only 313.4bhp

I was talking about my car with 40% trans loss. Scroll a few posts back please. Don't want to steel some of yours

SHEPSM3 wrote: WOW!  Thats alot of losses! Were your tyres flat?  I would suspect that the correcting calculations on thier dyno maybe a little suspect (PLEASE, NO OFFENCE INTENDED) thier figures maybe correct. The reason I asked is that I re-mapped a race E36 M3 3ltr with Unichip about a year ago. We do not have a dyno which calculates the losses, so I was interested in your road wheel figures. The car finally produced 202kw's(274bhp) at the wheels. The owner seemed very happy with this, but I wasn't sure?? I was expecting standard flywheel figure (286bhp/210kw's) to be at the wheels after mapping. If the car had 25% losses then that would say the car had 365bhp at the flywheel, but with 40% that would be a whopping 457bhp at the flywheel. I remember suggesting the car should have arround 20% losses and suggested his car had arround 340bhp, which is exactly what he was expecting with the modifications he had done. Incidently, the engine had higher compression ratio, schrick camshaft (I dont remember which one, but presumably race) small flywheel, ported head to match standard inlet manifold, larger exhaust manifold. I usually say between 18% and 25% depending on front wheel or rear wheel drive and taking into account tyre size and width, age of car, etc, etc. I always stress this figure is not the one to look at. The road wheel output is the one to look at. 4WD obviously has alot more losses. Nevertheless, I would expect about 220-230bhp at the roadwheels for a standard e36 3ltr M3.

 

So what are you saying ? 25% is now alot of loss !!! I thought Bmw themselves quote around 25% for transmission loss ?

Any loss in power has to be dissipated somewhere, and that somewhere is heat.

Could you imagine the heat in the drivetrain if there were a 46% loss!

I believe a figure of no more than 20-25% would be right.

When mine got dynoed it had 213.8 bhp or 167 at wheels, representing 22% calculated transmission loss. If BMW's 25% losses are to be believed then my power would be 222 on that dyno, just about bang on the 220 that BMW claim for an Evo2.

I think most people would be happy to believe the "overstated" figures that some dyno's give, if only for bar room talk and would keep going back to those machines. If they underestimated losses, making the max bhp figures lower, people would be moaning and never go back.

At the wheel figures are the only ones that can be measured properly without having the engine out on a bench rig so should be the ones used for comparisons

Here is an article I found, he believes the losses should be even less than 20%!

"When I started out writing these technical articles there was some sort of overall plan that the pieces would fit together in the end to form a picture of how maths and physics operate to determine how engines and vehicles work. The aim was to try and dispel at least some of the myth and bull**** that pervades the tuning industry in the attempt to make people buy tuning parts that aren't properly designed and don't work. Fundamental principles are very powerful tools to help us decide what is and what is not possible. Unfortunately most people don't have the maths or education to apply these tools. Hopefully this website will have helped those who want to learn to appreciate some of those fundamental principles. One of my biggest hobby horses is the supposed flywheel power figures that tuning firms and magazines attempt to derive from wheel bhp figures taken from rolling road tests. In the main these are vastly overinflated. Many people seem to think that as much as 30% or more of the flywheel power is lost in the transmission. A simple reposte to that is that gearboxes would melt if they soaked up so much energy but there are more powerful arguments to use. Copyright David Baker and Puma Race Engines

My own figures for transmission losses have been stated in previous articles but to recap they are usually no more than 15% of the flywheel power for FWD vehicles and no more than 17% for RWD ones. A good guide is to deduct 10% of the flywheel figure plus another 10 bhp for FWD and 12% plus 10 bhp for RWD. If you are starting from a wheel bhp figure then you have to apply those equations in reverse - add 10 bhp then divide by 0.9 for FWD or 0.88 for RWD to get back to a flywheel figure. Those figures were not just plucked out of thin air. They represent the culmination of many years of research and testing combined with the views of reputable companies like Bosch and VW.

There is however a final way of estimating what transmission losses really are based on the most accurate dyno in the world - the car itself. Physics tells us that it takes a certain amount of energy to push a given shape through the air at a given speed. The maths behind this is not open to debate. It's part of the basic physics that determines how the universe operates. The article on how top speed and engine power are related goes into this in some detail. The power available to force a car to its top speed is obviously the net power at the wheels after all tyre and transmission losses. If we can work out this net power and we also know the flywheel bhp figure then the transmission losses must be the difference between the two. To work out the power requirements of a car based on its top speed we need to know its drag coefficient and its rolling resistance. For light vehicles, like passenger cars, the rolling resistance is about 0.013 x the vehicle mass. Drag coefficients are measured and published by the manufacturers. If we take a couple of examples we can see how this required power ties in with the engine's flywheel bhp. The equations are explained in more detail in the previous article so read that first if you haven't already done so.

The 1.8 Vauxhall Astra GTE (new shape from 1985 on) has a frontal area of 20.5 sq feet and a Cd of 0.31. With two people and some test equipment on board (which is how most reputable magazines do their tests) the car weighs about 2460 lbs. The engine is rated at 115PS (about 113 bhp) and the tested top speed is about 123 mph. let's see how much net power is required to achieve that speed.

Rolling resistance power is 0.013 x 2460 x 123 / 375 = 10.5 bhp

Air resistance power = 20.5 x 0.31 x 0.00256 x 123 cubed / 375 = 80.7 bhp

Total bhp at the wheels must be about 91.2 bhp to achieve that speed. If we apply my formula for FWD cars to the quoted flywheel power we get (113 x 0.9) - 10 = 91.7 bhp at the wheels. Hmmm - so you gonna step outside and fight me about 0.5 bhp or is this starting to make some sort of sense? Copyright David Baker and Puma Race Engines

Let's try a more powerful car.

The 2WD Sierra Cosworth was rated at 205 PS (about 202 bhp). Top speed was in the 145 mpg region according to most magazines. Test weight with 2 people and 50 lbs of equipment on board is around 3060 lbs. Frontal area is 21 sq feet and Cd is 0.35.

Rolling resistance power is 0.013 x 3060 x 145 / 375 = 15.4 bhp

Air resistance power is 21 x 0.35 x 0.00256 x 145 cubed / 375 = 153 bhp

Total net power required is 168.4 bhp. Apply the RWD formula to 202 bhp and we get (202 x 0.88) - 10 = 167.8 bhp.

The conclusion here is pretty obvious. If transmission losses were as high as 30% then there just wouldn't be enough power left at the wheels to achieve the top speeds that the cars actually show. The Cosworth would only have 141 bhp at the wheels if this were the case and its top speed would therefore only be around 136 mph. You can work that out for yourself by applying the formulae above. The Vauxhall would only have 79 bhp at the wheels and be capable of around 117 mph. Copyright David Baker and Puma Race Engines

Of course every magazine test achieves a slightly different top speed and published drag coefficients vary a bit depending on the source. If you carefully select your data depending on what you are trying to prove you can show just about anything. But if you run enough of these calculations and also factor in the acceleration from computer simulations you start over the years to build up a picture of how things really work. The conclusion is that transmission losses are much lower than commonly quoted. The only reason to apply big transmission loss percentages is to flatter the supposed flywheel power outputs from poor tuning work.

Ask any tuning firm which applies these big transmission losses why they do so and about the best you are going to get in reply is "that's what we've always done" or "we read it in a book somewhere once". Hopefully a proper scientific argument like the above will be a bit more convincing. You don't even have to take my own word for it. All the equations I use are part of fundamental physics and commonly quoted. The book "Internal Combustion Engine Fundamentals" by J.B.Heywood is a good source and he is the professor of automotive engineering at MIT so dispute him at your peril."

Entirely agree with M3nally - the only thing that you can compare, and the only thing with a hope of consistency between Dynos is the "at the wheels" figure.

That said, my '98 M3 EVO made 236bhp at the wheels, which is at the lower end of the expected range for EVOs, according to the Dyno Man, so your 3.0 is not far behind at all at 224.

Reinforces the view that 3.0s make close to their stated 286bhp output, and EVOs are often a long way from 321bhp at the flywheel...

You have to convince people that your car somehow with minor modifications is making approx 24bhp above standard for that vehicle.

The only way I have seen this done is the removal of the AFM or in the case of a turbo by increasing the boost.

You may have convinced yourself but I do not think anyone else on here is convinced.

I am not and I have done quite a few Rolling road dyno runs on various cars and on various dynos - and I have never seen what you are experiencing.

There is only one explanation I can think of and that is the operator forget to change the calculations in his software when he changed cars from the 4WD evo and subaru to your car.

Karl

 

Karlp wrote: You have to convince people that your car somehow with minor modifications is making approx 24bhp above standard for that vehicle. The only way I have seen this done is the removal of the AFM or in the case of a turbo by increasing the boost. You may have convinced yourself but I do not think anyone else on here is convinced. I am not and I have done quite a few Rolling road dyno runs on various cars and on various dynos - and I have never seen what you are experiencing. There is only one explanation I can think of and that is the operator forget to change the calculations in his software when he changed cars from the 4WD evo and subaru to your car. Karl

lol. I dont have to convince anyone what power my car produces. I was just posting my experience on here. I wont bother in future !

I can tell by the way the car performs on the road that for some reason it is more powerful than other M3's. It was like this when it was totally standard. That is just my opinion and I dont care who believes it or not.

Also,my M3 ran 3 13.9 1/4's at santa pod when completly standard,I dont know what it would run now with the minor mods but I know it is quicker.

Ive compared my 1/4 mile times with other M3's and I think you'll agree its slightly quicker than the average.

Im not trying to prove anything here,just pointing out the facts that make me think the way that I do .

Also,it states on the power graph from the Dyno that it is set for 2wd manual transmission,so the operator did change from 4wd to 2wd !

Edited by 535i sport