M3 Dynotest

[lucid]

Originally Posted by swamp2

Well if that ain't apples to oranges I don't know what it (even if it is close to correct for an apples to apples comparo). If we don't have an actual measurement for a MT 335i I say the best estimate is measured weight with AT - (BMW official weight difference between MT and AT). This gives 3574-11=3563, making the measured M3 MT 11 lbs lighter than 335i MT. Close enough to call it a wash.

Unless we can find a magazine that happens to weigh both on the very same scale, it will always remain an apples to oranges comparison. Either way, the M3 seems to come in slightly lower than the 335i.

However, the confusing part is if we look at the BMW stated numbers (EU spec) for the M3 and the 335i, we we should see a difference of 45 kg. How come the measured numbers published on the website contradict that? Have they weighed the M3 with less than a full tank of gas? So, I'd say what is reported on that website is in question actually.

[Epacy]

Originally Posted by swamp2

This gives 3574-11=3563, making the measured M3 MT 11 lbs lighter than 335i MT. Close enough to call it a wash.

Just to be overly critical of any non-fact, this would and can be hotly debated to the point of zero substance. Debated until the weight values can be independently confirmed.
I value the current assumption but must also keep things in a relative frame of mind.

[Smoltz]

As per EU specs the M3 weighs 45kg more. Seems pretty straight forward to me.

In terms of actual weight. Until someone weighs two cars both with a basic equipment level with the same amount of gas, it's all guesisng (even if it's educated).

Furthermore, why would BMW lie about the weight, how do they benefit? In the 335i horsepower case, the car is underrated, but only so that the numbers aren't closer to the M3.

-Adam

[Epacy]

Originally Posted by Smoltz

As per EU specs the M3 weighs 45kg more. Seems pretty straight forward to me.

In terms of actual weight. Until someone weighs two cars both with a basic equipment level with the same amount of gas, it's all guesisng (even if it's educated).

Furthermore, why would BMW lie about the weight, how do they benefit? In the 335i horsepower case, the car is underrated, but only so that the numbers aren't closer to the M3.

-Adam

Justification established by other parties can be for reasons that would never enter our stream of conciseness.

[lucid]

Originally Posted by Smoltz

Furthermore, why would BMW lie about the weight, how do they benefit?

The only thing that comes to mind is some kind of weight based custom/tax classification in a specific market they care about. Some countries have engine displacement based taxation for instance. But that wouldn't explain why they'd report the M3 to be heavier than it really is.

[Smoltz]

Originally Posted by lucid

The only thing that comes to mind is some kind of weight based custom/tax classification in a specific market they care about. Some countries have engine displacement based taxation for instance. But that wouldn't explain why they'd report the M3 weight to be higher.

Couldn't dishonesty regarding the weight mean legal troubles for BMW from a dissatisfied owner?

-Adam

[lucid]

Originally Posted by Smoltz

Couldn't dishonesty regarding the weight mean legal troubles for BMW from a dissatisfied owner?

-Adam

Depends on the legal system I guess, and what kind of rationalization the company can come up with. A similar argument can be made regarding underating power: I lost control of the car because I've been told it had less power than it actualy did? Yeah, that's kind of a stretch, but...

[AMB]

So how do you explain Automobile Mag's dyno results for the 335i? Like I mentioned on a post over at 1addicts... (http://www.1addicts.com/forums/showthread.php?t=1180)

Are these guys just using the stock horsepower rating and assuming the drive train loss is whatever?

[dechoong]

Sorry if my questions sound stupid... does the rolling road test power at the wheels? How do you test power at crank then? When manufacturers quote BHP, are they refering to power at wheels or crank?

I've read reviews that a certain car tested by journalist actually produces more power on their rolling road test than the official quoted figures. Just like to clarify with the above questions.

[esquire]

Originally Posted by Epacy

Justification established by other parties can be for reasons that would never enter our stream of conciseness.

consciousness?

[Epacy]

Originally Posted by esquire

consciousness?

Yikes, I have been on a string of that lately.

[lucid]

Originally Posted by dechoong

Sorry if my questions sound stupid... does the rolling road test power at the wheels? How do you test power at crank then? When manufacturers quote BHP, are they refering to power at wheels or crank?

I've read reviews that a certain car tested by journalist actually produces more power on their rolling road test than the official quoted figures. Just like to clarify with the above questions.

A rolling road test is a setup where a set of rollers are connected to a dynamometer, and the drive wheels of the car ride on the rollers. So, that's power at the wheels. To measure power at the crank, you need to take the engine out and attach it to the dynamometer directly. That is obviously a difficult thing to do, so it is usually done my manufacturers. Manufacturers are rating the engine only and report power/torque at the crank shaft.

[dechoong]

Originally Posted by lucid

A rolling road test is a setup where a set of rollers are connected to a dynamometer, and the drive wheels of the car ride on the rollers. So, that's power at the wheels. To measure power at the crank, you need to take the engine out and attach it to the dynamometer directly. That is obviously a difficult thing to do, so it is usually done my manufacturers. Manufacturers are rating the engine only and report power/torque at the crank shaft.

Thanks for the explanation.

Wow... that means the mentioned car produces a shitload more power at the crank than its official quoted figures since its tested power at the wheel is already higher the figures officially quoted at crank. Kudos to the manufacturer... no wonder their cars almost always outperform their official figures .

[Epacy]

Originally Posted by dechoong

Wow... that means the mentioned car produces a shitload more power at the crank than its official quoted figures since its tested power at the wheel is already higher the figures officially quoted at crank.

[dechoong]

Originally Posted by Epacy

I was refering to the 997 GT3. Engine power is quoted at 415ps (409bhp), but EVO rolling road test shows 429bhp at the wheel. Take into account of drivetrain loss, that meant its actual engine power is quite a lot more than the officially quoted 415ps.

[Epacy]

Didn't know what car you were referring to.

[bruce.augenstein@comcast.]

Originally Posted by dechoong

I was refering to the 997 GT3. Engine power is quoted at 415ps (409bhp), but EVO rolling road test shows 429bhp at the wheel. Take into account of drivetrain loss, that meant its actual engine power is quite a lot more than the officially quoted 415ps.

I don't know anything about EVO's test, but would be willing to bet that the 429 number is an estimated one, generated from the at-the-wheels figure they observed. Some chassis dynos do this "automatically", given a user-supplied figure for estimated drivetrain friction and rolling resistance. A 15% loss has been the traditional number for longitudinally mounted engines.

If the observed, at-the-wheels figure was really 429 hp, that would mean the powerplant is generating 140 hp per liter, which stretches the bounds of credibility for a street driven, emissions legal, normally aspirated engine. Not even Honda has done that. As far as I know, they still hold the record at 120 hp per liter in the 2-liter S2000.

Based on more or less standard torque per liter limits (in the low 80's), you're looking at 9000+ rpm in order to come up with that sort of power yield.

Motorcycles? Yes. GT3? Nope.

Absolutely terrific car, though. Wish I could afford one.

Bruce

[dechoong]

Originally Posted by bruce.augenstein@comcast.

Some chassis dynos do this "automatically", given a user-supplied figure for estimated drivetrain friction and rolling resistance. A 15% loss has been the traditional number for longitudinally mounted engines.


Bruce

I'm not technically astute, so what you've said could possibly be true

[chonko]

Originally Posted by AMB

So how do you explain Automobile Mag's dyno results for the 335i? Like I mentioned on a post over at 1addicts... (http://www.1addicts.com/forums/showthread.php?t=1180)

Are these guys just using the stock horsepower rating and assuming the drive train loss is whatever?

In my humble opinion most people are measuring the power and torque at the wheels and using a percentage losses to work out the stock crank numbers. This of course is making people to believe that actually numbers are overrated.
This methodology is wrong, because the frictional losses as a percentage of the stock numbers varies at various engine speed although the actual loss remains doesn't. Most engines above 2000 rpm will give you an approximately constant drive-train losses(approximately 10 ft.lbs variation in torque losses above 2000 rpm)

[lucid]

Originally Posted by chonko

Most engines above 2000 rpm will give you an approximately constant drive-train losses(approximately 10 ft.lbs variation in torque losses above 2000 rpm)

Hmmm...I can see where you are coming from, but I must assume that in an ideal world, at higher rpms, things don't necessarily interface/mesh the way they do at lower rpms. For instance, there can be additional vibrations that result in additional loads on the friction surfaces. Also, what happens to the heat generated at those surfaces at higher rpms when it might not be transferred as effectively per unit time, and how does that affect bearing/gear geometries and thus friction? And, what happens to lubricants and their effect on friction? (I am assuming the coefficient of friction for steel to steel contact without lubrication is fairly temperature insensitive, but I don't know for sure.)

Regarless, even if the absolute torque loss is indeed fairly constant across the rpm range, the power loss will increase linearly with increasing rpms since hp = (torque * RPM) / 5250, which is the trend the measured power curve exhibits in relation to the stated crank power curve for the E92 M3 in the graphs referenced by the OP.

[AMB]

Originally Posted by chonko

In my humble opinion most people are measuring the power and torque at the wheels and using a percentage losses to work out the stock crank numbers. This of course is making people to believe that actually numbers are overrated.
This methodology is wrong, because the frictional losses as a percentage of the stock numbers varies at various engine speed although the actual loss remains doesn't. Most engines above 2000 rpm will give you an approximately constant drive-train losses(approximately 10 ft.lbs variation in torque losses above 2000 rpm)

Maybe I'm missing your point, but they did compare it to the non turbo 330i which should have a similar drive train.

"That’s roughly a twenty-percent loss. Since they have similar drivelines, you’d expect the 335i to put down 235 hp and 250 lb-ft. But it didn’t. It put down a whole lot more: 275 hp and 300 lb-ft."
http://www.automobilemag.com/feature...i_dynamometer/

I could understand if they were a lot closer in numbers, but that's quite a large difference. Proof to me that BMW strategically underrate some of their cars.