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      09-18-2019, 04:06 PM   #24

Drives: 2014 335i
Join Date: Jul 2017
Location: SoCal

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2014 BMW 335i  [0.00]
Originally Posted by MartinS View Post
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?
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.