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      09-19-2019, 11:19 AM   #45
DPelletier
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Quote:
Originally Posted by upsidedownfunnel View Post
These driveline loss estimates are nowhere near an exact science. The 15% number bandied about is actually not accurate. Different cars with different differentials, final drives, transmissions, transfer cases, wheels, etc. all will vary in how much loss they have. That's why when you see a tuner estimate the bhp "assuming" a 15% driveline loss, that is complete B.S.

The reason most just use percentages is because things like the differential, transmission, and the general durability/weight of these components are probably matched to the power output of the vehicle. A smaller car would have lighter components since heavier components would be unnecessary and slow the car down more.

Also, as engine power goes up, a lot of these loss forces are amplified which is why using a percentage is more appropriate than a fixed power figure. However, even this is not totally correct as these changes are not perfectly linear. So the loss is really dynamic and even depends on which gear you're in.
Good post and good points. That said, I'd expect the driveline losses for the M40I to be between 10-15% ;-)

....it's just an approximation to give us a rough idea of what the chassis dyno numbers translate to in net crank hp.


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      09-19-2019, 11:22 AM   #46
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Originally Posted by F30Allen View Post
Just curious, does anyone know if the B58 on the Z4 is the same as the Supra? The Supra community has unlocked a lot of HP and assuming they're the same then the numbers should be similar to the Supra.
The Euro Z4 and Supra use the B58B30M1 whereas the 382hp versions use the higher spec B58M30O1. There are significant hardware differences between the two versions.



Dave

Last edited by DPelletier; 09-19-2019 at 11:32 AM..
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      09-19-2019, 11:25 AM   #47
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Quote:
Originally Posted by mecheng77 View Post
Why does Bmw consistently do this? Insurance, regulation, laws?
Quote:
Originally Posted by mecheng77 View Post
Why does Bmw consistently do this? Insurance, regulation, laws?
Yes; HP does affect insurance. I remember hearing this a long time ago.
Also had an insurance agent mention that as well.

Also it plays into TCO when they do comparisons among competitors.
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      09-19-2019, 11:27 AM   #48
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Quote:
Originally Posted by upsidedownfunnel View Post
Is all of this based on just that one post by a vendor that is selling tunes? I'd take that with a pretty large grain of salt.
well, a member dynoed his "382hp" version at 374hp at the wheels and posted the results so it isn't just one post. https://g29.bimmerpost.com/forums/sh....php?t=1621271 ....and what do you think the vendor would gain by reporting false info? ....I mean, wouldn't we be all more likely to buy upgraded "tunes" if the numbers were lower? A false lower number would show a larger increase after a tune right? .....I don't see the advantage for the vendor to over-report the baseline dyno results


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      09-20-2019, 06:38 AM   #49
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Quote:
Originally Posted by CanAutM3 View Post
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Originally Posted by helloelectro View Post
It's a percentage of your total.
Well, actually it is not.

There are many different components to drivetrain loss that individually vary to different degrees to load and road speed. So even a blanket percentage is a false assumption.

It is just better to leave the whp numbers as they are avoid trying to speculate crank power from them.
Which I totally agree with .... but then we start talking about different dynos, different days, fuel quality, ambient conditions etc lol. No way to know all cars compared to each other ... best way us probably to compare a couple head to head same day with same fuel.... or just stop caring about the EXACT figure by X vs Y vs Z methods which is where I've ended up haha
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      09-20-2019, 07:32 AM   #50
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Quote:
Originally Posted by evanescent03 View Post
Which I totally agree with .... but then we start talking about different dynos, different days, fuel quality, ambient conditions etc lol. No way to know all cars compared to each other ... best way us probably to compare a couple head to head same day with same fuel.... or just stop caring about the EXACT figure by X vs Y vs Z methods which is where I've ended up haha
Exactly
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      09-20-2019, 06:48 PM   #51
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      09-21-2019, 01:30 AM   #52
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Quote:
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Originally Posted by DPelletier View Post
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Originally Posted by gheumann View Post
You're measuring at the rear wheels, yes? Then I'd say they're better than BMWs numbers which are presumably just the engine?
Yep, I assumed that's what he was trying to say?...... 15% driveline loss would put it at around 448hp net flywheel and 10% would put it at 424hp net flywheel. Good numbers in any case. :-)

Funny thing was when I first test drove an M40i and was worried about the power compared to my V8 Ftype, the sales manager said that BMW typically underrates their engines and that the net flywheel rating would be what I could expect at the rear wheels.....guess he was right on the money. Car certainly felt faster than I expected though the 400lb weight advantage vs. my F type was responsible for some of that...

Dave
Why do people say the loss in % in the transmission?
15% on a 1000hp engine would be 150hp loss but only 15hp loss in a 100hp engine.

My M4 has about 64hp loss in the driveline. That would be 64hp loss nomatter how many hp it has, right?
The powertrain loss is the function of many variables including input power and temperature. The more power is generating more heat and the result is more power loss. Its completely nonlinear function but still depends on input and components' behaviour...
It also varies per designs as other said 10-15%
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      09-21-2019, 08:00 PM   #53
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Quote:
Originally Posted by mecheng77 View Post
Why does Bmw consistently do this? Insurance, regulation, laws?
Consistently do what?

BMW doesn't underrate their engines. The Power rating is as installed at the output shafts, not engine brake power.
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      09-27-2019, 05:54 PM   #54
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Nice numbers....I am excited to see what engine tunes start becoming available. Would love to get my car in the 425-450 range.
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      09-27-2019, 06:07 PM   #55
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Originally Posted by str86diesel View Post
Nice numbers....I am excited to see what engine tunes start becoming available. Would love to get my car in the 425-450 range.
Then you're going to love what we're seeing here:



More info on this build soon.
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