M4 dyno test by Sportauto 465hp/577 nm

[CanAutM3]

Originally Posted by swamp2

NOT the % as a function of rpm (as you have previously identified) but the total amount of loss increasing steadily with rpm! It being roughly described to a constant percentage is also reflected by the P(loss) expression above. Are the losses absolutely flat, no but close enough!

If that is your position now, then we are in agreement

Originally Posted by swamp2

You've been on this "kick" for sometime. Let's examine in more detail and I believe you will agree that the "fraction" is the principal majority (I guess still a fraction but the implication of "only a fraction" is incorrect as to me this implies a minority contribution).

I chose my words carefully when I mentioned efficiency. And yes, only a relatively small fraction of transmission efficiency varies with rotational speed.

I fully agree though, for a constant torque, the absolute power losses increase with RPM. And this is where it becomes interesting, with the broad power plateau of the S55, power losses in absolute terms do not increase much with RPM across the power plateau.

Originally Posted by swamp2

(as you have previously identified)

It is not me but you that quoted an efficiency formula that drastically varies with RPM. I have been disputing this since.

Originally Posted by swamp2

Let's say we call the 15% number the loss, ℓ

Thus ηtf = (1 - rpm x ℓ/redline)

Originally Posted by swamp2

Yes, absolutely agree that inertial drivetrain effects are present in inertial dynos, but attempts can be made to reduce these with slower ramp speeds. P=Ixα*ω (rotational analog of F=ma and P=Fv, metric of course...), thus when α (angular acceleration) is low or zero so is power.

It is not all inertia dynos that also have a "brake" feature; and without a brake, there is no way to control the acceleration rate. Also, different dynos have different drum sizes and inertias, hence some of the variability between dynos. Brake dynos that run in steady state eliminate the inertial impacts altogether.

Doing a quick exercise, taking the wheel and tire weights from the EAS thread and assuming a dyno run that takes 13s to accelerate from 3000 to 7400rpm in 5th. I figure it takes about 10hp to accelerate only the rear wheels and tires at 7000 engine RPM. Add the discs, hubs, half-shafts, diff, driveshaft, transmission and engine and the overall inertia can have a quite meaningful impact on the output reading.

Originally Posted by swamp2

Lastly, as you know, the effective mass declines steadily with higher gears, another reason not to inertially dyno in low gear.

While this is correct when evaluating the acceleration capabilities, it is not necessarily true when measuring power on a chassis dyno. For a given engine RPM band, the higher the gear used, the more power gets consumed to accelerate the drivetrain over a broader and higher RPM range. Using the same parameters in the calculation above, except using 3rd gear instead, yields about 4hp to accelerate the wheels and tires.

Originally Posted by swamp2

This is not a defense/endorsement here of inertial dynos. My quick "statistical" summary prior shows just how typically inaccurate they are. The point here is more to show that the Maha and inertials are not totally incompatible and both must include drivetrain (and tires) losses which are in the 15% range (manual, RWD).

I figure that the ~12-20% discrepancy between chassis inertia dyno readings and the actual engine power depends on the following factors depending on the dyno and selected gear:

~2-5% Tire losses
~2-5% Inertial impacts
~8-10% Drivetrain efficiency

Anything above that has probably more to do with poor heat management of the test environment.

[CanAutM3]

Originally Posted by w3rkn

300hp vs 450hp...
or
300ft-lbs vs 450ft-lbs..

Without knowing anything about each^.. the TQ figures tell more of a story than the static HP numbers.

Compare two very similar chassis with different engines: E9X 335d and M3.

425lb-ft and 265hp vs 295lb-ft and 414hp.

Guess which one is faster .

Engine torque without gearing means absolutely nothing in terms of vehicle performance. It seems to me you have some fundamental misunderstandings of basic physics .

[Audio Fan]

Originally Posted by CanAutM3

Compare two very similar chassis with different engines: E9X 335d and M3.

425lb-ft and 265hp vs 295lb-ft and 414hp.

Guess which one is faster .

Engine torque without gearing means absolutely nothing in terms of vehicle performance. It seems to me you have some fundamental misunderstandings of basic physics .

As noted above, you need to take into consideration the entire curve, not just the peak. The diesels typically have a tall, low RPM peak, and as such, won't have a wide, high torque band. That's why you have to look at the area under the torque curves. My guess is that the M3 still has a much wider torque curve, but doesn't peak as high (higher area under the curve), and the 335d has a fairly narrow curve with a big peak at low rpm (lower area under the curve). The F8X maintains the diesel peak over a wide band => big area under the curve. No need to guess.

[swamp2]

Originally Posted by w3rkn

Not going to argue I've spent countless hours in debate with you, only to have you admit later the importance of TQ. And how you COULD NOT explain things, without first running your simulations... and when they didn't work out for your, you were lost. You then had to find new software, that accounted for a flat torque curve... before you understood TQ deltas.

But it clearly appears you do want to argue...

Utter rubbish. Torque and power are like apples to oranges. Much more below.

Originally Posted by w3rkn

Horsepower is a man-made # the represent work done, its a static figure. TQ is not..

Neither torque nor power are any more or less "man-made". Again rubbish. Each has a precise definition and one determines acceleration with LESS information and hence is MORE useful and fundamental to vehicle (ANY VEHICLE) performance, car, bike, rocket, aircraft, tank, etc.

Originally Posted by w3rkn

1) The torque curve is the rate of acceleration in any gear.. PEROID!
2) The car with the most torque (not peak torque, but MOST throughout the powerband), will accelerate the quickest.

Nope, wrong, 100%. They have a SIMILAR but not identical shape. Since one is vs. TIME on the x axis and the other vs. rpm and those are not linearly related. Torque curves can and do inform one about the FEEL of the acceleration but not how much of it there actually is. And who has the fundamental misunderstandings here? The vehicle with the best time averaged power accelerates the best, period. Basic physics, no gearing knowledge required whatsoever.

Originally Posted by w3rkn

Have you still not grasped this^, perhaps you need to look at power & tq, from a non-automotive perspective? to truely understand the relation of each and that HP is a static number. Or play with something mentally without gears..? (Do you understand electric motors power delivery?)

My understanding comes from a GENERAL understanding of the math and physics, yours obviously does not.

Originally Posted by w3rkn

300hp vs 450hp...
or
300ft-lbs vs 450ft-lbs..

Without knowing anything about each^.. the TQ figures tell more of a story than the static HP numbers. Even if you plot two cars TQ curve against each other.. you don't even need HP plots, to guess/figure what one is faster..

If these are the peak values with any typical sort if ICE curve shapes the higher power car will be significantly faster, regardless of torque. Again, what is it about peak values vs. knowing the entire curve is so difficult for you to grasp? Did you miss the results I showed long ago where one can double the peak torque of an engine and barely affect overall performance? You simply can not do that with power, physically impossible.

Originally Posted by w3rkn

HP plots means very little as peak HP is all that matters. It's static, where as torque defines and tells the whole story about the engine. TQ speaks directly to the characteristics of the engine.

Utter rubbish again. For a single simple metric (i.e. one number) peak hp is massively more informative since it is intrinsically gear independent. If you want to know more second best and pretty well complete knowledge is the full hp curve. This is obviously much more information required (theoretically infinitely more information, but practically perhaps just 20 times as much for 20 data points) but also provides complete performance information (along with weight of course). Next to last as to what it tells one about performance is the entire torque curve. Although basically equivalent to knowing the hp curve it is less informative by itself as one MUST know gearing to do ANY meaningful calculations of acceleration (or simply convert back to power). Lastly, knowing peak torque is the least informative and pretty well tells us NOTHING about performance.

Please show me a basic calculation, the math, formula and result that allows torque alone to compute an instantaneous acceleration value. Surprise, surprise, there isn't one. Here is the trivial math for you using power (makes NO difference what gear you're in - cool isn't it)

a = P/(v*m) (all SI units, power is wheel power of course).

Do some comparisons vs. real world test data. Wow, what a surprise it actually works. Share your wonderful, powerful insightful method or cork it, really.

Originally Posted by w3rkn

But youy already know this and admit as much..

But in the end, you concede^

Wow, talk about a problem with reading comprehension. The quotes of mine you provide in no way support your conclusions above. Quite unbelievable...

Originally Posted by w3rkn

The dyno plot is the engine.
A simulation is just another visual aid on what that plot means in every gear, given pure acceleration. Software works great in theory, but falls apart once there is ANY... and I mean ANY... wheel slippage, or 3k launch. Everything matters when dealing with simulators... as you start talking about ad nauseam and incremental Nths..

Nonsense. Modeling wheel spin is not easy and will never be perfect. However, the approach in CarTest is reasonable as it accounts for the key elements of weight transfer and a different (lower) coefficient of friction during wheelspin. The software Quarter Pro appears to handle this well as well but you can debate that with forum member bruce.augenstein@comcast as he helped the author with the wheelspin models.

Originally Posted by w3rkn

That is why a simple dynograph compared equally to others is just effective... if you know how to read them, (or if their written in your language).

Dyno's are pretty well rubbish as most of those here with a demonstrated understanding of them and a clear grasp of the basic physics (and observed capabilities) all firmly agree.

Welcome to your own personal little island of misperceptions, false beliefs, lack of foundational understanding. It must be a lonely place there. Honestly, it is time to write your own simulator (as I have done) to better understand these subtleties.

[swamp2]

Originally Posted by CanAutM3

It is not me but you that quoted an efficiency formula that drastically varies with RPM. I have been disputing this since.

That was clearly an error. What I meant to say/construct through a formula was simply that power losses are a linear function of rpm. Good catch. Not sure how I brain farted that one so badly. It is not from a lack of understanding, just being quick and careless... Sorry this wasn't noted prior.

[swamp2]

Originally Posted by CanAutM3

Engine torque without gearing means absolutely nothing in terms of vehicle performance. It seems to me you have some fundamental misunderstandings of basic physics .

Whew, another voice of reason with conclusions supported by the physics...

[CanAutM3]

Originally Posted by swamp2

That was clearly an error. What I meant to say/construct through a formula was simply that power losses are a linear function of rpm. Good catch. Not sure how I brain farted that one so badly. It is not from a lack of understanding, just being quick and careless... Sorry this wasn't noted prior.

[Kurt_OH]

Swamp2 gets it.

Glad he took on the mantle of understanding and sharing.