M4 dyno test by Sportauto 465hp/577 nm

[Boss330]

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. Either way, I am holding back until I see a dynojet dyno but chances are that the WHP graph will look near identical.

I hope you aren't saying that 2+2 doesn't equal 4 in the real world...???

But hopefully rather that sometimes, when we had anticipated or planned on 2+2 being the numbers we would work with, that we find out that in the real world we weren't able to achieve exactly 2.00 but ended up with 2,1+2,05 which equals 4,15.

And don't count on a different kind of dyno to show the same RWHP (as explained by CanautM3)

[phear_me]

Originally Posted by Boss330

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

Then why show the uncorrected RWHP on the graph? It's terribly misleading.

[myzmak]

20 odd years ago, I spent the first year of my university life in the College of Engineering.

...and as soon as it was done, I ran away as fast as I could into something that made sense, like German existential philosophy. This thread reminds me of those early days.....

Fascinating reading all of this. At some point, I'm sure some of us would take kindly to some sort of translation/interpretation of this (for the 'philosophically inclined').

[ASAP]

Originally Posted by phear_me

Then why show the uncorrected RWHP on the graph? It's terribly misleading.

exactly

[CanAutM3]

Originally Posted by phear_me

Then why show the uncorrected RWHP on the graph? It's terribly misleading.

As I posted previously:

Originally Posted by CanAutM3

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

[phear_me]

Originally Posted by CanAutM3

As I posted previously:

I completely disagree that other dynos only show this "incorrect" rear wheel horsepower because they are cheap. On almost every dyno output that I've ever seen the RWHP line graph is attempting, within a couple percent variance, to replicate the actual horsepower making it to the wheel. The HP/Torque at the wheel is the number that everyone cares about because those are the numbers that actually move the car. Flywheel HP is being calculated off of the RWHP since this is what is actually measured on the runners. To show inaccurate RWHP with a loss figure to get to a Flywheel HP number really seems to be putting the cart before the horse. I get wanting to show the math - but that's just not the way most dynos output the data. You get torque and HP curves that are supposed to be representative of reality.

Here is an example:



Note the 12% loss factor:

411 RWHP * 1.12 = 460HP, which is, magically, the Flywheel HP rating for the Corvette Z51.
385 RWHP * 1.12 = 431HP, which is, magically, the Flywheel HP rating for the BMW M4.

[ASAP]

E46 M3 MAHA Dyno for comparo

[Black Gold]

^^^^^^

the engine power makes sense for the e46, but that whp is 40 whp too low. maybe that's your point, but those cars hit 270-280 stock to the wheels on dynojet/mustang all day long

[ASAP]

^yep... which is why I think the curve is probably about right but the WHP numbers are about 40 WHP low... which would make sense for this new car given about 400 WHP and it's trap speed numbers so far from the vbox.

[s62]

See the loss in the E46 M3 dyno and it may seem 'too large' too. But the flywheel power is spot on.

I wouldn't like to clutter the thread with more Maha dynos, this time of the F10 M5, but if you search around and you look at them you see the same thing. The loss is big and sometimes the rpm are off, perhaps only on the graph, but the bhp numbers are good.

What we know is that whp and powertrain loss are calculated the same way, which is intrinsically consistent. So I don't really look much into that. Maha dyno is as good a chassis dyno as we get to estimate engine power with a margin of error of 2% according to Boss330

[tooch]

Guess we'll have to wait for a comparison of some kind. Something def looks a lil off.

[FogCityM3]

More dyno confusion.

This is why I love my Dash Dyno unit. Plugs into OBD port, shows tq to the wheels, calculated HP, adjusts for gear ratio, temperature, pressure, speedo correction, Cd, frontal area, and is done on a flat road at speed, giving full cooling/intake pressure effect and all SAE adjusted. Corroborates very closely with the "actual moment" internal dyno that the ECU calculates (can see this using the BT tool). Just start at the same RPM, use a road marker on the same road.

http://www.dashdyno.net

[Sedan_Clan]

I can't wait for this car to come out so that people can just stop bitchin' and drive the damn thing.

[CanAutM3]

Originally Posted by phear_me

I completely disagree that other dynos only show this "incorrect" rear wheel horsepower because they are cheap. On almost every dyno output that I've ever seen the RWHP line graph is attempting, within a couple percent variance, to replicate the actual horsepower making it to the wheel. The HP/Torque at the wheel is the number that everyone cares about because those are the numbers that actually move the car. Flywheel HP is being calculated off of the RWHP since this is what is actually measured on the runners. To show inaccurate RWHP with a loss figure to get to a Flywheel HP number really seems to be putting the cart before the horse. I get wanting to show the math - but that's just not the way most dynos output the data. You get torque and HP curves that are supposed to be representative of reality.

Here is an example:



Note the 12% loss factor:

411 RWHP * 1.12 = 460HP, which is, magically, the Flywheel HP rating for the Corvette Z51.
385 RWHP * 1.12 = 431HP, which is, magically, the Flywheel HP rating for the BMW M4.

Why do you think the entire industry uses flywheel power ratings and not wheel power ratings?

Where does that 12% loss number come from? It is simply a gross approximation and is in no way accurate, not all cars have the same loss. There is inherent variability in roller inertia dynos that can significantly alter that "loss" level and the power reading (how tightly the car is tied down, the acceleration rate used or the gear used, just to name a few). In terms of chassis dynos, wheel hub brake dynos are much more accurate and repeatable to measure wheel HP, but they need to be run is steady state to get meaningful results.

My present understanding of the Maha dyno is that it performs a first run to measure how much power is needed to accelerate the dyno. It then performs a second run to establish the losses and inertial impacts. Adding the two numbers yields very decent numbers for flywheel power and torque. On the Maha dyno, the WHP number shown is simply the actual measurement taken as part of the process to establish the flywheel power.

For more discussions on dynos, see this thread starting with post #40

[solstice]

Originally Posted by CanAutM3

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.

I think your explanation is spot on. This is a dyno to show the power of the S55, everything else is just factors to calculate that. The whp curve and level here is utter useless in itself since we aren't given the split between dyno and drivetrain losses, or a dyno losses compensated whp curve. What a pity with such a good setup that we just get the engine power and not really good numbers and curve on how much power is getting to the wheels. Anyhow 465ps at the flywheel shows a similar under rating as we are now becoming used to from the N54 and S63. The early N54s gave around 340 hp while rated at 300 and I think the S63 has been calculated to give around 600 hp while rated at 560 hp. So around 40 hp under rated engines across these. This should put to ease those who were moaning about the 430 ps and had hoped for 450+. The engine has ample power.

[damnitBobby]

these dyno numbers have no value

dyno numbers are good for showing delta's (if done on the same dyno) and, for you bench racers, doesn't mean jack shit for bragging rights.. each dyno is calibrated differently and will never be a universal number you can brag about

let's see some trap speeds at the 1320

[Chako]

Some dynos just read lower than others. We should also get a MAHA sheet from a stock E92 M3 (the E46 is very helpful), and then you will have a great WHP comparison.

For example, this is a Mustang dyno sheet for E92 M3. Stock 325WHP, whereas a Dynojet usually ended up at ~350WHP.

[CanAutM3]

Originally Posted by Chako

We should also get a MAHA sheet from a stock E92 M3 (the E46 is very helpful), and then you will have a great WHP comparison.

I don't think this is true.

Depending on the conditions, the "Schlepp"/drag factor may be different for the different cars being tested. Again, IMO, the only numbers that can really be compared are the flywheel power and torque numbers.

[CanAutM3]

Originally Posted by ASAP

E46 M3 MAHA Dyno for comparo

Pretty darn accurate IMO. The S54 was rated at 343ps @ 7900RPM, that is 1.7% error.

Again here, the WHP number is meaningless by itself.

[aus]

Originally Posted by damnitBobby

[B]these dyno numbers have no value]/B]

dyno numbers are good for showing delta's (if done on the same dyno) and, for you bench racers, doesn't mean jack shit for bragging rights.. each dyno is calibrated differently and will never be a universal number you can brag about

let's see some trap speeds at the 1320

Well, it does suggest the S55 makes more power than it's rated for and that it runs out of breath above 5,500 RPM- regardless of what the redline is.

.

[CanAutM3]

Originally Posted by aus

and that it runs out of breath above 5,500 RPM- regardless of what the redline is.

What makes you think that

I see an engine that keeps on building more power until 6600RPM and then barely drops off until 7300RPM.

[phear_me]

Originally Posted by CanAutM3

Why do you think the entire industry uses flywheel power ratings and not wheel power ratings?

Where does that 12% loss number come from? It is simply a gross approximation and is in no way accurate, not all cars have the same loss. There is inherent variability in roller inertia dynos that can significantly alter that "loss" level and the power reading (how tightly the car is tied down, the acceleration rate used or the gear used, just to name a few). In terms of chassis dynos, wheel hub brake dynos are much more accurate and repeatable to measure wheel HP, but they need to be run is steady state to get meaningful results.

My present understanding of the Maha dyno is that it performs a first run to measure how much power is needed to accelerate the dyno. It then performs a second run to establish the losses and inertial impacts. Adding the two numbers yields very decent numbers for flywheel power and torque. On the Maha dyno, the WHP number shown is simply the actual measurement taken as part of the process to establish the flywheel power.

For more discussions on dynos, see this thread starting with post #40

The industry uses HP at the fly in modern times because it's a higher number and therefor more marketable to the average schmo who doesn't know thedifference. Useable RWHP is a much more important metric than HP at the fly for exactly the reasons you state here - not all cars have the same loss! But the variance is still small.