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      07-28-2011, 06:05 PM   #1
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M3 engine HP overrated vs dyno vs drivetrain losses

There have been questions raised in some other posts regarding this topic but I'm wondering if there is any conclusive explanation into the following.

Sufficient time has now passed to gather a wide range of dyno results from different owners. The average range appears to be in between 325-335 RWHP. There are dyno results showing 350-370+RWHP that are OUTSIDE this average range, however anyone understanding the nature of dynos and how results can drastically change with parameters, conditions, strap down, etc can understand this variance. Pencil Geek has already demonstrated how going from 91 octane gas to 93+ makes a huge difference in HP results as well. Long story short, the dyno is primarily meant to be used as a before/after tuning tool that can give you consistent results and NOT as a tool for absolute measurements to compare "power" from one member's car in Cali to one in NY which can be almost random/near meaningless.

Furthermore, drivetrain losses are not static-state fixed % that can be used to derive engine HP from a dyno reading. But we of course all do it using the standard rule of thumb of 15%MT-20%AT. Based upon my experience, although drivetrain losses are a crude way of trying to estimate engine HP from a dyno, it normally isn't substantially far off from manufacturer's specs for MOST vehicles.

However, based upon the numerous dyno results out there, what I don't understand is whether our M3s have higher than normal drivetrain losses in the 20-22% range or perhaps the engines are slightly overrated? Or is there another explanation of why the M3 dyno results don't seem to correlate to engine specs using the standard rule of thumbs as most other vehicles do?
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      07-28-2011, 06:56 PM   #2
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All I can tell you is some of these dyno numbers on this board were disappointing until put in perspective. My perspective is why would BMW, a company that has been underrating HP for years now start overrating horsepower. I think I can trust them to evaluate horsepower in a car this good. And remember their HP figure is at the crank. Maybe the Germans have some special measuring device for that, I don't know. All I know is for right now I don't need a car any faster than this or I could get into some real trouble. In other words, I agree with you but I don't care that much anymore. The car is wonderful.
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      07-28-2011, 07:06 PM   #3
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Not all dynos are created equal. Some are more conservative than others.

I think in general it should be used as a tool to gauge performance gains and not as absolute. Plus there are many variables to consider.

It's best to try to at least use the same dyno for obvious reasons.
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      07-28-2011, 07:54 PM   #4
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I'm surprised we've yet to see any on an engine dyno. Especially with these companies that are building low compression and/or stroker motors. None have been on a dyno or if so not posted on here yet
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      07-28-2011, 08:06 PM   #5
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The trick is to first consider that a dyno is just a tuning tool that happens to provide a calculated output value for your bragging plesure. Second is to run a car on multiple dynos (at different shops) in the same general conditions and see how consistent the values are.
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      07-28-2011, 09:17 PM   #6
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Quote:
Originally Posted by J08M3 View Post
I'm surprised we've yet to see any on an engine dyno. Especially with these companies that are building low compression and/or stroker motors. None have been on a dyno or if so not posted on here yet
I'm not surprised personally - coming from Audi's and Subaru's I never once saw any tuner put an engine on an engine dyno.
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      07-28-2011, 10:49 PM   #7
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I always wondered this too. Seems like the s85 usually dynos around 450 which makes sense for 507hp.
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      07-28-2011, 11:58 PM   #8
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This is a good discussion. Now let's assume one guy is in California, and another guy in New York and they are both running on the same brand and model of dyno. Why can't you compare their dyno results after SAE correction? That's exactly what SAE-J1394 was designed to do. Granted it's not perfect, but nothing is. But I've seen plenty of people say you can't compare dyno results in different places due to weather differences. Yet that's exactly what SAE-J1349 is designed to compensate for. So why can't you compare?
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      07-29-2011, 06:17 AM   #9
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Quote:
Originally Posted by img View Post
This is a good discussion. Now let's assume one guy is in California, and another guy in New York and they are both running on the same brand and model of dyno. Why can't you compare their dyno results after SAE correction? That's exactly what SAE-J1394 was designed to do. Granted it's not perfect, but nothing is. But I've seen plenty of people say you can't compare dyno results in different places due to weather differences. Yet that's exactly what SAE-J1349 is designed to compensate for. So why can't you compare?
Everyone in NY uses 93 octane. But I suppose they could buy 91 instead so you could compare
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      07-29-2011, 06:38 AM   #10
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Hi,

I thought about it.. (i'm owner of an M3 too). I'm wondering about intake:
- enought ventilation on dyno for our 3 intake's entry ?
- M3 have only one intake for 8 cylinder..compared to 2 intake for the V8 M5 e39 or the V10 M5 e50 & M6

Akra's dyno are closed, big ventilation and air conditionned for example.
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      07-29-2011, 06:40 AM   #11
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Quote:
Originally Posted by apexi View Post
Long story short, the dyno is primarily meant to be used as a before/after tuning tool that can give you consistent results and NOT as a tool for absolute measurements to compare "power" from one member's car in Cali to one in NY which can be almost random/near meaningless.

Furthermore, drivetrain losses are not static-state fixed % that can be used to derive engine HP from a dyno reading. But we of course all do it using the standard rule of thumb of 15%MT-20%AT. Based upon my experience, although drivetrain losses are a crude way of trying to estimate engine HP from a dyno, it normally isn't substantially far off from manufacturer's specs for MOST vehicles.
Excellent topic which I am glad has been raised by an end user for once.

I have covered this topic before on forums and not many people have taken notice of how dyno numbers can vary.

The purpose of a dyno is to measure the delta in measured power as part of a development programme or for getting an estimate between one particular setup to another.

As for the drivetrain loss - I think it would be helpful if I started posting readings from different cars and you can compare them to the M3.

We can go into far more depth by analysing correction factors, strapping etc etc.

Again, thank you so much for bringing this up!
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      07-29-2011, 06:40 AM   #12
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Setting aside most of the variables that give slightly different readings from one dyno to the next, I have noticed a trend of around 330-340rwhp on average for the M3's, which doesn't really add up to 414hp at the crank...however, trap speeds and quarter mile times seem to indicate at least 400hp.

My 03 Cobra dyno'd 372rwhp stock, which was about the norm for that model car, and it was rated at 390hp...really putting down around 425 at the flywheel. That car ran 12.77 @ 111 bone stock and weighed in about the same as the M3 (3650lbs for the Cobra) and my 05 GTO put down 355rwhp and was rated at 400.

I personally believe the car has the power, it just puts it down "strangely"...maybe gearing has something to do with it...who knows. I don't really care about dyno's too much anymore, actual performance numbers are better IMO.
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      07-29-2011, 11:38 AM   #13
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There are two things we are looking at here;
1) Comparison of cars on different dyno's
2) Drivetrain loss calculation and what approximate flywheel calculation the S65 is making

So let's go over these briefly for now and any questions that follow we can then start looking at in some more depth.

1) Comparison of the same car (E92 M3) on the same and different dyno

I have found in the BMW community that not many dyno operators (and there are a few!) talk about this subject too much. I have spoken to dyno operators across the world and some have said they feel nervous about this subject because if people knew everything then people would not take them more seriously.
We think the opposite and have posted on many forums about the dyno. We believe people should understand. It is quite clear that this lack of understanding has created confusion in the community and worse still some people going to the point of saying dyno’s are useless.

I would hope that people would take our points seriously as we do dyno a very large number of M power cars all year round for quite some years now.

First thing first. We know that weather conditions have an effect on engine power. Humidity levels, barometric pressure and temperature all individually effect engine power.
The majority of dyno’s have SAE correction factors built into them along with a weather station which measures humidity, pressure and temperature. The values are input into a forumula and the end result is the correction factor.
The correction factor corrects for the atmospheric condition under which the engine is being tested under.
The problem we have found (as many other dyno operators have found) is that these correction factors assume all engines will respond in exactly the same way as each other given a change of any of the above mentioned variables in any permutation or combination.
This is not true unfortunately and this is part of the reason why we get varying numbers especially under extreme changes in weather condition where the correction factor will also change massively.

Here is an example of an S62B50 V8 engine (BMW E39 M5) tested on our dyno dynamics machine.
Exactly the same tyres and fuel:



Notice how the graph shapes are almost identical! Small differences are there because slightly different ignition targets are reached due to the ECU actually taking some of the atmospheric conditions into account but not as much as the dyno is assuming! The dyno SAE correction factor is simply ‘over compensating’ because what it thinks should happen simply is not happening with this engine. What the dyno software should be doing is showing the car to make the same power on these two very different days..... that's what correction factors are meant to do! This is not an isolated example. This is however an extreme example but you get the point.
We have also seen different brand of tyres, final drive ratio’s and of course strap tension cause skewing of the dyno graphs.

What also can make a big difference is the gear used and I know for a fact that some dyno operators prefer to use 4th and some prefer 5th. You simply cannot compare.

Fuel of course plays a major role but this we all know and don’t really need to discuss here as we are talking about the comparison of cars with the only variable being the atmospheric conditions (hence the correction factor) and dyno operator.

There are further variables at play too which I have discussed very recently which are the type of cooling fan used, allowing ignition targets to be met and generally allowing the inlet, oil and coolant temperatures to reach an equilibrium. We will discuss this in more detail.

Just from the above brief information I am sure you can deduce that the same car can read so so differently on even the same brand of dyno on different days! Even the very same dyno can have varying figures on the same car because someone decided to change from normal street tyres to semi slick. Yes gentlemen, this also makes a difference.

Luckily for many, we do have some excellent dyno operators around who are also lucky to have very consistent weather conditions.
Typically the effects of using different types of tyre, final drive and the correction factors playing a role will skew the dyno graph. The shape of the graph will not however change and more emphasis needs to be put on studying the shape.

What also needs more emphasis is the logging of ignition advance and AFR. Thanks to certain members of the community this has been highlighted but only a handful of people look at this information correctly.

The dyno should be used in a more detailed way and is really for comparisons of upgrades and more importantly from our point of view as a development and test rig.


2) Drivetrain loss calculation and what approximate flywheel calculation the S65 is making

There are many dyno brands which attempt to calculate the flywheel power of an engine from the rear wheel horsepower made.
Two such dyno’s are the Dyno Dynamics and MAHA.
Dyno Dynamics uses a simply percentage addition to the RWHP which is set by the shootout mode selected.
For the S65 it’s shoot 8 (meaning 8 Cyl NA engine).
The MAHA uses a completely different method where the RWHP along with the coast down frictional losses. These are are combined to work out the flywheel power.

Why am I talking about this?

Well, both read fairly close to each other in terms of RWHP and the calculated flywheel calculation. They also both read very close to the stated manufacturer stated power and torque if used correctly.

Let us take some examples from our Dyno Dynamics readings across different BMW models and from there you can make up your own mind if it’s realistic or not.

Average Dyno Dynamics readings on Evolve Dyno for different STOCK BMW models:

BMW E36 M3 3.2 (Euro)
Stated Power – 321PS / 316HP
Average Tested Wheel Result – 250HP
Flywheel Calculation – 310HP

BMW E46 M3 (Euro)
Stated Power – 343PS / 338HP
Average Tested Wheel Result – 265HP
Flywheel Calculation – 330HP

BMW E39 M5
Stated Power – 394HP
Average Tested Wheel Result – 325HP
Flywheel Calculation – 395HP

BMW E60 M5
Stated Power – 507HP
Average Tested Wheel Result – 408HP
Flywheel Calculation – 497HP

BMW E92 M3
Stated Power – 414HP
Average Tested Wheel Result – 335HP
Flywheel Calculation – 410HP

I can post numerous (hundreds for some cars!) dyno graphs of the above cars to confirm all of this.

What’s more interesting is that the dyno graphs related to the above tests show calculated torque figures to be very very close to the stated torque from factory which in my opinion really does suggest that the calculation of around 18-20% drivetrain loss is very very accurate. I have never ever seen anyone look at it from this angle and those of you who are intelligent will agree that if both the flywheel calculated HP and torque are close together then it’s a very good estimate.

Hopefully the above will generate some more questions and we can look at certain areas in more detail.
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      07-29-2011, 12:57 PM   #14
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This topic has been covered numerous times. That is why dynos need to be taken with a grain of salt.

Real world times such as vbox runs 60-120 are more practical.
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      07-29-2011, 01:00 PM   #15
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Great post as usual Sal. Thanks man!
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      07-29-2011, 01:16 PM   #16
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Sal,

Unfortunately the graph alone doesn't tell the whole story about
SAE correction. For both runs, can you please provide the
UNCORRECTED horsepower, ambient temperature, ambient pressure, and
relative humidity. 8% correction is outside of the SAE
specification and would be invalid to begin with. I tried to look
at your graph to get the ambient conditions to run through the SAE
calculator, and came up with only 5% correction. But I had to
guess some of the numbers because the resolution of the image is
too low to see the numbers accurately. So it would be great if
you could post the uncorrected HP, along with all of the ambient
conditions for both runs to double check these results.
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      07-29-2011, 01:49 PM   #17
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Quote:
Originally Posted by img View Post
Sal,

Unfortunately the graph alone doesn't tell the whole story about
SAE correction. For both runs, can you please provide the
UNCORRECTED horsepower, ambient temperature, ambient pressure, and
relative humidity. 8% correction is outside of the SAE
specification and would be invalid to begin with. I tried to look
at your graph to get the ambient conditions to run through the SAE
calculator, and came up with only 5% correction. But I had to
guess some of the numbers because the resolution of the image is
too low to see the numbers accurately. So it would be great if
you could post the uncorrected HP, along with all of the ambient
conditions for both runs to double check these results.
Unforunately Dyno Dynamics graphs cannot be shown uncorrected.
Big flaw in my opinion in the software!

I think you however missed the point of it. This is not an analysis of this extreme example but an example to show SAE corrections don't always work. I can post loads of examples similar to this.

The car has had nothing changed. Just a different day of testing.

The whole point of SAE correction is to maintain the power no matter what the ambient conditions. Clearly this is not working.

The correction factors are 8% apart and the power difference average through the rpm range is 5% apart.

It does work on some cars!

I can give you all the detail you want and you can manually correct back.

The correction factors shown are the actual ones so you will get the same results as myself.

To calculate manually the uncorrected figures you just add 8% and 1% on the graphs.
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      07-29-2011, 01:53 PM   #18
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Quote:
Originally Posted by jimmyeatsworld View Post
This topic has been covered numerous times. That is why dynos need to be taken with a grain of salt.

Real world times such as vbox runs 60-120 are more practical.
For development and same day testing with everything kept equal they are a very clear guide to what's going on.

I do agree with your statement about real world results though, that cannot be denied.

The dyno gains should mirror the on road performance gains.
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      08-04-2011, 01:02 PM   #19
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One piece of data missing from the dyno db is the mileage on the motor at the time of the dyno.

I believe this may be a significant factor on the S65. My suspicion is that the average for e9x M3s dyno'ed with say 10k miles would be higher than those dyno'ed with very few miles.

I think this motor gains more hp as it wears in a bit, than from say a cat back/filter/pulley.
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      08-04-2011, 01:49 PM   #20
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Some of these same dynos that are supposedly the fault for the surprisingly low readings seen from the M3 are probably ones that would also give surprisingly high readings for the 335i. The M3 seems to typically make slightly less than BMW specifies when using the common drivetrain loss factor of 15%, while the 335i seems to make slightly more than BMW specifies when using the same 15% factor. One car may be overrated by BMW and one car may be underrated.
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      08-05-2011, 04:11 PM   #21
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Quote:
Originally Posted by pbonsalb View Post
Some of these same dynos that are supposedly the fault for the surprisingly low readings seen from the M3 are probably ones that would also give surprisingly high readings for the 335i. The M3 seems to typically make slightly less than BMW specifies when using the common drivetrain loss factor of 15%, while the 335i seems to make slightly more than BMW specifies when using the same 15% factor. One car may be overrated by BMW and one car may be underrated.
We test as many 335's on our dyno as M3's. That's alot of cars tested.

The quoted different in HP of the two different cars is 108HP.

What do we actually see? Around 100-110hp difference on average.

That's the important fact for us.

I am aware that in the US, 335i's make nearly the same power at the wheels as the manufacturer suggests should be at the flywheel.
However......... we don't see this and quite frankly none of the european tuners see this.

Something is up with the testing of 335's in the US.

Even still, it still doesn't matter. The dyno is used to show a difference.
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      08-05-2011, 05:04 PM   #22
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Quote:
Originally Posted by Sal@Evolve View Post
We test as many 335's on our dyno as M3's. That's alot of cars tested.

The quoted different in HP of the two different cars is 108HP.

What do we actually see? Around 100-110hp difference on average.

That's the important fact for us.

I am aware that in the US, 335i's make nearly the same power at the wheels as the manufacturer suggests should be at the flywheel.
However......... we don't see this and quite frankly none of the european tuners see this.

Something is up with the testing of 335's in the US.

Even still, it still doesn't matter. The dyno is used to show a difference.


Dynos as you have thoroughly stated are a tool. A tool for an engine tuner to optimize the car and see what changes are made. It is not meant to scrutinize a manufacturers engine ratings.
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