M4 dyno test by Sportauto 465hp/577 nm

[ASAP]

Originally Posted by CanAutM3

I have no idea how this dyno works and what the "losses" represent. But the math works, at 7000RPM for example: 240 P-Rad + 120 P-Schlepp = 460 P-Mot.

I think the only numbers that we can really look at to compare anything are the flywheel power and torque numbers.

I think you may have just realized how math (as I've stated before both to you and swamp) will not always equate to the real world. Either way, I am holding back until I see a dynojet dyno but chances are that the WHP graph will look near identical.

[CanAutM3]

Originally Posted by s62

It measures the parasitic loss directly during the deceleration. This is how it arrives at the flywheel power.

How is this done? I guess in neutral? I still don't understand the 30% loss...

EDIT: The only thing that I can think of is that the "losses" include the inertia and drag of the dyno rotating components.

[CanAutM3]

Originally Posted by ASAP

I think you may have just realized how math (as I've stated before both to you and swamp) will not always equate to the real world.

[Powaup]

Originally Posted by JoeFromPA

Mercedes 2.0 liter in the CLA AMG, Subaru and Mitsubishi have made 2.0 liters putting out around 150 hp/liter for quite awhile....probably a few others. By no means common, but also not a new achievement in forced induction in terms of specific output either.

true forgot about those cars, EVOs and STis get 300 hp out of their 2L turbos CLA 45 amg might be the winner with 177.5 hp/L

[CanAutM3]

Originally Posted by solstice

It does seem from the whp chart that power drops pretty significantly after 6k rpm. It does look enough to create a feel of running out of breath ( I did not say jerk ) even if maximum acceleration might be with shifts at 7k rpm. This make me continue to believe that significant short shifting is the most pleasurable way to drive this thing.

Don't assume this yet.

As I posted previously, I don't think we can compare the WHP number here to typical chassis dynos. The measurement and calculation methodology of this dyno seems quite different. The only numbers that mean anything are the flywheel torque and power numbers (P-Mot and MMot on the graph).

[s62]

Originally Posted by CanAutM3

How is this done? I guess in neutral? I still don't understand the 30% loss...

Yes, in neutral

[CanAutM3]

Originally Posted by s62

Yes, in neutral

I edited my post after you responded...

Do you think the "losses" also include the dyno inertia and losses? 30% could make more sense this way.

[phear_me]

Originally Posted by CanAutM3

How do they figure drivetrain losses ? 30% loss at max RPM seems awfully high to me (~135/465)

This is important to understand if the flywheel 465ps number is to mean anything.

I'm also confused here. The Fly HP and RWHP (Rear Wheel Horse Power) are way off. There shouldn't be this much loss. As others have stated should be about 12% - 15% max.

EDIT: My guess is the RWHP is the right number and the math to get to Fly HP is different than what we are used to.

385 RWHP (Prad) * 1.12 (loss factor recapture) = 431 Fly HP.

[CanAutM3]

Originally Posted by phear_me

I'm also confused here. The Fly HP and WHP are way off. There shouldn't be this much loss.

I think I have a theory. This type of dyno measures how much "brake" power is produced while accelerating the car's drivetrain and the dyno. It then measures how much "brake" power is needed to slow both of them down in neutral. Adding the two numbers together would yield the flywheel power produced. It is legit, but the WHP numbers cannot be compared to other chassis dynos.

[phear_me]

Originally Posted by CanAutM3

I think I have a theory. The dyno measures how much power is produced while accelerating the car's drivetrain and the dyno. It then measures how much power is needed to slow both of them down in neutral. Adding the two numbers together would yield the flywheel power produced. It is legit, but the WHP numbers cannot be compared to other chassis dynos.

What's more likely: (i) The dyno BHP is correct and BMW is understating their BHP by 35 (ii) the dyno RWHP is correct and BMW is accurately stating their BHP?

I hope I am wrong because I would love to find out I just got another 35 HP - but somehow I don't think so.

[E36toF30]

Originally Posted by CanAutM3

I think I have a theory. This type of dyno measures how much power is produced while accelerating the car's drivetrain and the dyno. It then measures how much power is needed to slow both of them down in neutral. Adding the two numbers together would yield the flywheel power produced. It is legit, but the WHP numbers cannot be compared to other chassis dynos.

Yeah, that sounds like a plausible explanation.

Originally Posted by phear_me

What's more likely: (i) The dyno BHP is correct and BMW is understating their BHP by 35 (ii) the dyno RWHP is correct and BMW is accurately stating their BHP?

I hope I am wrong because I would love to find out I just got another 35 HP - but somehow I don't think so.

That explanation doesn't account for why the losses are so high (as a % of flywheel HP) at high rpm.

Also, other BMW turbo engines are known to be underrated, so 35 hp more than their rating wouldn't be out of the ordinary I think.

[solstice]

Originally Posted by CanAutM3

I think I have a theory. This type of dyno measures how much power is produced while accelerating the car's drivetrain and the dyno. It then measures how much power is needed to slow both of them down in neutral. Adding the two numbers together would yield the flywheel power produced. It is legit, but the WHP numbers cannot be compared to other chassis dynos.

That's a good possible explanation but wouldn't it make the flywheel hp incomparable instead of the whp? I.e you have an extra boost in the flywheel formula here while the rwd hp is what is measured? Unless you mean that other dynos compensate for the dynos losses through calibration? You would think that the sportauto graph would have shown a compensated rwd hp graph as well though if this is the explanation.

[ASAP]

So why is the whp curve dropping past 6k? No one can answer that and it has nothing to do with math.

[GregW / Oregon]

Originally Posted by Powaup

Damn that's nuts. What other car has as much hp/L? I can't think of one

BMW i8 3-cylinder has 154 hp/L (231 hp from 1.5L), so it's not surprising this engine is dynoing around twice the horsepower at twice the size.

[solstice]

Originally Posted by ASAP

So why is the whp curve dropping past 6k? No one can answer that and it has nothing to do with math.

I think canAutM3 suspects that the dyno is causing the losses that drags down the whp at higher rpms.

[CanAutM3]

Originally Posted by solstice

That's a good possible explanation but wouldn't it make the flywheel hp incomparable instead of the whp? I.e you have an extra boost in the flywheel formula here while the rwd hp is what is measured? Unless you mean that other dynos compensate for the dynos losses through calibration?

My understanding is that most chassis inertia dynos interpolate power based on how fast a car's powertrain can accelerate the dyno mass. The dyno losses are included in the interpolation formulae.

The methodology used here is far more accurate as it removes drivetrain losses, tire slip losses, drivetrain, wheel/tire and dyno inertia from the equation. The only variable that it would not account for is the engine inertia (note tha the higher the gear used the less impact it has).

[solstice]

Originally Posted by CanAutM3

My understanding is that most chassis inertia dynos interpolate power based on how fast a car's powertrain can accelerate the dyno mass. The dyno losses are included in the interpolation formulae.

The methodology used here is far more accurate as it removes drivetrain losses, tire slip losses, drivetrain, wheel/tire and dyno inertia from the equation. The only variable that it would not account for is the engine inertia (note tha the higher the gear used the less impact it has).

Then why show flywheel hp compensated for dyno losses but not show whp compensated for those losses. Doesn't add up to me.

[CanAutM3]

Originally Posted by ASAP

So why is the whp curve dropping past 6k? No one can answer that and it has nothing to do with math.

I hope I am not losing my time responding to you...

It all has to do with math and physics.

Power needed to accelerate a mass at a given rate increases with speed. The faster the dyno roller spins, the more power you need to keep accelerating it. Same for the drivetrain. This is why you see the P-Schlepp number increase with speed. If the engine produces a constant power output as the speed increases, you will see a decrease in the power measured at wheels on this dyno.

[CanAutM3]

Originally Posted by solstice

Then why show flywheel hp compensated for dyno losses but not show whp compensated for those losses. Doesn't add up to me.

Simply because the WHP and "Schlepp" are the actual measured numbers from the dyno to be able to calculate Engine power and torque. WHP is not really relevant. It is seen often because it is the only thing "cheap" dynos can measure.

[Boss330]

Originally Posted by ASAP

So why is the whp curve dropping past 6k? No one can answer that and it has nothing to do with math.

The answer is in the dyno graph, and it's about maths...

The blue line is WHP, the green line is losses. As the rpm's increase, so does the losses.

Just take the P-Mot curve and subtract losses for each rpm and you get P-Rad.

The decline in WHP therefore is simply a function of the increase in losses as explained by CanAutM3 above. The engine makes a quite stable flywheel HP reading, but as losses increase the WHP falls (obviously).

It's basic maths to calculate the WHP from the P-Mot and subtract P-Schlepp

[Boss330]

Some info on one type of MAHA dyno:

http://www.maha.de/single-roller-dyn...eLocaleAttr=en

2% accuracy on WHP
1400kg inertia mass

[Powaup]

Originally Posted by GregW / Oregon

BMW i8 3-cylinder has 154 hp/L (231 hp from 1.5L), so it's not surprising this engine is dynoing around twide the horsepower at twice the size.

might have even more hp once it gets dynoed