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      09-19-2019, 08:44 AM   #41
Second Lieutenant

Drives: 2018 BMW m240i
Join Date: Jan 2019
Location: Dallas,TX

iTrader: (1)

Originally Posted by MartinS View Post
Originally Posted by helloelectro View Post
Originally Posted by MartinS View Post
Originally Posted by DPelletier View Post
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...

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?
Based on your car 'always' having a 64hp loss. If your car had 50hp and you have a 64hp loss, your example would mean your car has -14hp. The power loss from wheel to crank is a percentage of the total, and changes relative to the increase or decrease in power, it's not a static number.
What I mean is that I know it has a 64hp loss. So if I put pure turbos on and get, let's say 250hp more, then I still have a 64hp loss... or?
No. It's a percentage of your total. Also, your loss is at the wheels (whp) not at crank(flywheel/bhp)

75whp = 100 at crank

This is a soft figure of difference btw. It's what most people use to assume crank power when seeing wheel power.

The 64 hp loss you are noting was derived from a % factor. It will change with the gains/loss in hp.

200hp at wheels =~ 230hp at crank = 30hp difference
400hp at wheels =~ 460 at crank = 60hp difference.

Again, this is fuzzy logic that just makes it easy to assume crank hp. But it typically amounts to 15% difference.