Driveline Loss

[Super Drager]

Have a read of this thread and tell me what you think.

http://www.aus300zx.com/forum/showthread.php?t=298899

Theres no way a drivetrain will keep losing say 20%, for example a 100hp car would have 80rwhp, modify the engine to 200hp and now its losing an extra 20hp, the driveline only needs a certain amount of power to move it why would it sap an extra 20hp??

Edited March 28, 2010 by Super Drager

[Duncan]

lol....way to start a fight!!!!

what if the friction/heat/power loss is directly related to the torque you push on it with?

on the other hand....does a 1000hp drag car effectively have a 200hp heater in the gearbox??

[PM-R33]

A topic that has been discussed on this forum a million times.

Here's the last thread discussing it:

http://www.skylinesaustralia.com/forums/Bh...drivetrain+loss

And here's my post that is as accurate as you are going to get:

We all roughly know what a standard RB25DET is rated at the engine and we all roughly know what they make at the wheels standard. There's about a 60-80HP loss give or take depending on the condition of things.

So depending on the extra power (say an increase of 200HP at the wheels), i re-ad the 60-80HP loss (since you aren't going to magically lose less power through the drivetrain as power increases unless you have done something out of the ordinary). This will give you roughly your minimum amount of power at the engine. Then i take into account that as power increases, losses through heat, noise, friction ect. increase. Depending on the added power i say it might lose an extra 10HP or something like that.

It is rough, but atleast you know roughly what it would be.

You know what the car losses through the drivetrain from factory.

Example, the old GTS HSV Monaro's. Rated at 300kw, make about 220-240kw@wheels.

Standard GTST, rated at 180 odd kw, make anywhere from 120-140kw@wheels.

So if the same GTST makes another 110kw@wheels to 250kw@wheels, we re-add that 60-40kw loss, so it pumps it up to 290-310kw@engine. However the engine is now producing more power, therefore everything is slightly increased in loss. This is the figure that can not be given by a percentage, or a fixed linear figure. It varies. I'm sure there would be a close equation you could do to work it out more accuretly. The more power you make, the higher the additional loss through friction, fluids, heat etc.

So in a bit of a maths equation.

kw@motor = kw@wheels + original factory loss (say 50kw to be a nice number) + 'unknown variable' (additional loss as power increases)

= 250kw@wheels + 50kw original loss + 'x'

= 300kw@motor + 'x'

This 'x' value is one that you have to guess logically. It aint going to be 100kw, it aint going to be .5kw. A good educated guess in this case could be 5kw. It will obviously slightly increase with the more power you are making. at 1000kw@motor it might be 50kw.

That is about as accurate as you can get with guessing, and for most people i think it is good enough to have that minium value and a little bit extra. I'd rather under qoute something than over qoute.

[Duncan]

lets face it....your flywheel does not drive the cars....the tyres do.

other than just a bigger number, or maybe comparison to a factory car claim....what relevence is a flywheel power figure?

[Duncan]

actually, I reckon we should quote "spark plug kilowatts". since internal combustion engines are only about 40% efficient a standard gtr makes over 800spkw

[PM-R33]

lol