how much bhp loss on 4wd rolling road ?

[A1quattro]

just got the rally car back from jaspeed ,had it on the rollers max bhp 255 , max torque 377@ wheels with 34mm restricted fitted and on pump fuel, so quite happy [always want more] trying to work out how much power at engine ,am i wright in thinking we loose 30% on 4wd cars and 20% for 2wd, any one know correct figure ?

[A80Avant]

too much for 30%

some say 25% for 4wd cars and i think that is also overrated

[A1quattro]

if i add 20% that gives me 306bhp and 452 torque

[Val]

so, nobody has ever taken off propshaft and tested car on rollers with center diff locked?

[Jamo]

so, nobody has ever taken off propshaft and tested car on rollers with center diff locked?

why you would do this?

Drive train loss is different per car and different dyno's have different ways of calculating it and is biggest bone of contention on dyno results.

If they didn't calculate it then I would say realistically a 20% loss is a good start.

The defacto value used is 25% but I do think that is high

[terrybullwon]

You need to go to a engine dyno then to a 4 wheel dyno then you will have the loss. Its the only way to get a real world %

But this is pretty motor sport budget stuff

[speeding-g60]

034 has done back to back testing on engine dyno and chassis dyno.... and have come up with ~18-22% drivetrain loss.

[Rusty]

Mine was ~240 at the wheels and ~300 back calculated at the fly.

[Avantus]

You can't really put it in %, but only in true numbers.

a 300hp vs a 600hp car with the same drivetrain won't have double the losses.

[A1quattro]

The rally car was fitted with a standard 01e dsy box when on rollers 255@ wheels , will i gain any more bhp when the 01e dogbox is back in the car[curently having 4.375crw/p and plated lsd fitted]