First BMW M4 GTS dyno = 492hp at crank

[FC4]

Originally Posted by CanAutM3

While it is true that there is no known GTS S55 that has been bench tested with power measured at the "flywheel", all the numbers posted so far do seem to be "at the crank" and not at the wheels.

Ah, ok. Yeah...that hasn't happened, either. I don't see anyone measuring anything "at the crank."

[CanAutM3]

Originally Posted by FC4

Ah, ok. Yeah...that hasn't happened, either. I don't see anyone measuring anything "at the crank."

The dynos used seem to have some way of measuring/assessing/estimating drivetrain loss and back calculate power at the crank. While I understand how this is done on a brake chassis dyno such as the Maha, I have not seen it explained how it is done on an inertia dyno like the dynojet. Something to follow...

[Boss330]

Originally Posted by FC4

Ah, ok. Yeah...that hasn't happened, either. I don't see anyone measuring anything "at the crank."

Quite correct, no one (apart from BMW and type approval authorities) have had a GTS engine on a dyno. The dyno results we have so far are CALCULATED crank hp numbers. WHP is measured and drivetrain/coasting losses are measured afterwards. The WHP plus measured drivetrain losses equals a theoretical crank hp number.

Dynos like a MAHA measures and calculates crank hp within a very close range to the real crank number. The INSORIC as used by Auto Bild has also proven to be very close to real crank hp numbers on a wide range of vehicles.

The posted number from Auto Bild is IMO more than likely within a maximum of 3-5% deviation from the engine dyno number.

[Boss330]

Originally Posted by CanAutM3

The dynos used seem to have some way of measuring/assessing/estimating drivetrain loss and back calculate power at the crank. While I understand how this is done on a brake chassis dyno such as the Maha, I have not seen it explained how it is done on an inertia dyno like the dynojet. Something to follow...

AFAIK it's as simple as letting the car coast down after a run with the clutch depressed. The rate of deceleration of the dyno rollers in this scenario is the measured drivetrain loss. Obviously not correct since the coasting is done on an unloaded drivetrain (and on the wrong side of the gears in the diff and gearbox), but a rough estimate on drivetrain losses is achieved.

[VCP]

It is all quite theoretical. My Dyno dynamics in corrected mode will add the theoretical drive train loss whatever the software is set at. 12%-15% is norm. Different shops will ask for different software. The most crucial thing here is consistency with your dyno. I can load the dyno to hold back up to 1000hp. Playing with that setting will change to corrected # also. Consistency and using the same dyno ideally with similar atmosphere conditions is the most important thing here. For the record I did a baseline C63 507 last week and the uncorrected # was 442 add 15% loss to 508. Very close to claimed crank 507

Originally Posted by Boss330

Quite correct, no one (apart from BMW and type approval authorities) have had a GTS engine on a dyno. The dyno results we have so far are CALCULATED crank hp numbers. WHP is measured and drivetrain/coasting losses are measured afterwards. The WHP plus measured drivetrain losses equals a theoretical crank hp number.

Dynos like a MAHA measures and calculates crank hp within a very close range to the real crank number. The INSORIC as used by Auto Bild has also proven to be very close to real crank hp numbers on a wide range of vehicles.

The posted number from Auto Bild is IMO more than likely within a maximum of 3-5% deviation from the engine dyno number.

[raysspl]

A factory beast at the dyno!

[Trevorstein]

I know … old thread here!

Correct me if I'm wrong??

* 492 (-13%) = 428 RWHp (+-). correct?

If so, My M4 ZCP (Dynojet) came out (on 6th run!) to

*404 RWHp

That is only - GTS +24Hp???

[CanAutM3]

Originally Posted by Trevorstein

I know … old thread here!

Correct me if I'm wrong??

* 492 (-13%) = 428 RWHp (+-). correct?

If so, My M4 ZCP (Dynojet) came out (on 6th run!) to

*404 RWHp

That is only - GTS +24Hp???

Wrong !

[Trevorstein]

Originally Posted by CanAutM3

Wrong !

Ok. So, please correct me here. How does it work!?!


Cheers!

[CanAutM3]

Originally Posted by Trevorstein

Ok. So, please correct me here. How does it work!?!


Cheers!

First, you can’t take a random loss number just like that to make any conclusions.

Second, different dynos will read differently. There’s no point comparing absolute numbers between different dyno. Chassis dyno are mainly useful to measure relative gains from modifications on a given car with before-and-after runs.

[Trevorstein]

Originally Posted by CanAutM3

First, you can’t take a random loss number just like that to make any conclusions.

Second, different dynos will read differently. There’s no point comparing absolute numbers between different dyno. Chassis dyno are mainly useful to measure relative gains from modifications on a given car with before-and-after runs.

Ok., but everything is subjective and relative! Everything is as on point or as pointless as you want it to be.

If you want to look at it that way, most people use measuring tools such as balance scales, watches, etc. & Dyno's
to have a baseline idea of where things stand.

"11~14%" Albeit arguably "random", I believe is the generally accepted range to calculate drivetrain loss, isn't it?

So, is my Math. wrong?


Cheers!

[CanAutM3]

Originally Posted by Trevorstein

Ok., but everything is subjective and relative! Everything is as on point or as pointless as you want it to be.

If you want to look at it that way, most people use measuring tools such as balance scales, watches, etc. & Dyno's
to have a baseline idea of where things stand.

"11~14%" Albeit arguably "random", I believe is the generally accepted range to calculate drivetrain loss, isn't it?

So, is my Math. wrong?


Cheers!

Yes, your math is wrong because you are comparing apples to oranges. There's no "acceptable" arbitrary number for drivetrain loss as there are too many variables to factor. You either measure whp or crank hp. You don't try to derive one from the other without actual loss measurements.

On the same dyno, on the same day, in the same condition, and in the same gear, in all likelihood an M4GTS will be making ~11% more peak power than a stock M4 CP. Further, the M4GTS will have a much fatter power curve across the entire powerband making it faster than just the peak power numbers suggest. Doodling with numbers to try to show it is significantly less than that is just pipe dreaming.