ROLLING ROAD AUDI S4.

[BRETTCOLLINS]

can anyone tell me if there is anythink special you have to do to 1998 Audi S4 Bi-turbo's to run them on a running road and get full power output.

took to 30 + car to a rolling road shoot out on sunday, all cars power runs were where they should have been, some car were standard, some modded.
there was only to audi's there both 1998 audi S4's both modded.
one with MTM chip.
one with AMD chip rs4 parts.

the mtm car run 250bhp and the amd car run 298bhp.

Amd run my car on there rollers a week ago showed 361bhp.

[Dippy]

Hi Brett,

As you probably know, RRs measure power at the wheels and use a conversion factor to calculate the flywheel power. Maybe this factor was not correctly applied on Sunday.

Was the RR a 4-wheel one? Were there any other 4WD cars there?

I'm a bit surprised your car only showed 361bhp at AmD...

[BRETTCOLLINS]

engine advantages is where the rollin road is, yes there was other 4wd cars, 3 escort cosworths, 2 scooby, they all run about right. have wheel power of my car and fly wheel power.

power at wheels is 223bhp.

[Dippy]

Well losses are around 40%...

[JohnW]

223 / 298 = 0.75.
Looks to me like they only used a 25% loss figure.

using dippy's figure of 40% gives
223 / 0.6 = 371 bhp.

Sounds about right to me.

[BRETTCOLLINS]

Do the audi S4's loss 40% power from fly wheel to the wheels. thats alot.

are cosworths and scooby the same?

[wazza]

It's always been about 25% loss on mine.

[BRETTCOLLINS]

thats what i was told abot my S4. Will speak to AMD about was what the wheel figures are on my car.

thanks people

[JonnyX]

The power loss through the drivetrain and parasitic losses are irrelevant of the power output hence it makes no sense to use
a percentage figure for anything quantitive. Normally the drivetrain losses and rolling resistance are factored in by letting
the car deccelerate on the rollers. The drivetrain losses I have seen on an S4 seem to vary from 60 bhp to 100+bhp
dependent upon the car, rolling road, wheels, tyre pressure etc. Personally I wouldn't bother. The rolling road gives you
the measured power which is what should be interesting anyway.

[Prawn]

This is why the guys in the states always work on whp as the use of
loss figures and ways to calculate it / fudge the figures are numerous.

Measured whp is the best measure, even though its not as good a number to
brag about in the pub.

[Dippy]

As JonnyX says, there are proper ways to factor in the losses. However in typical RR shootouts, fudge factors are used. 25%/40% are typical for 2WD/4WD.

[BRETTCOLLINS]

Easy way round this, AMD are getting me my power figures at the wheels for my car, Then I can see if there is any difference between them.