cuprabob

Hi any one know how much power or percentage can be lost from the engine power on a cossie 4x4 basicaly if the cars running 300 or 350 bhp at the wheels what power should be at the flywheel any can anyone check there rolling road reports and let me know what sort of difference there is thanks.

oldford

It's has been a while, but I know we measured 90 - 92 bhp of loss on an Escort Cosworth with 300 bhp at the flywheel. Maybe this rolling road exaggerated a bit, but the minimum loss would something like 70 bhp.

cuprabob

thanks for that anyone else got any ideas also check your rr print outs if you could cheers

m4tt274

iTrader: (2)

isnt it meant to be 25%
i was producing 229bhp at wheel and the operator said about 300 @ fly

cuprabob

i think you may be right i read some where 2wd cars can be about 15-18% and most not all 4wd cars are about 20-25% i just wanted to see what other people's results were any more takers cheers

tabetha

I know mine was 259@wheels, 297 crank, on low boost, but it's 2wd, I'd expect 4wd to be between 25 to 30%, some are nearer 35 though.
Simple way to find out is get it on the rollers that can actualy measure precisely the trans loss in coast down test, you'll have exact firgures of wheels and flywheel then.
tabetha

oldford

It is my believe that the transmission loss is a fixed number of bhp, not a percentage.
I have tuned a lot of cars and usually had them on a rolling road before and after. The transmission loss was always almost the same (plus or minus 1 bhp).
Lets say I have a car with standard 300 bhp and 4-wheel drive. Put it on a rolling road and measure 200 bhp on the wheels and 100 bhp losses. Then I tune the engine to 600 bhp (supercharger, No2 injection, you name it) with same rev range as standard and measure it again. If the loss is 33%, I would now have 200 bhp loss. But the transmission has not changed. So, I would still measure the same 100 bhp loss.

pete mcrash

iTrader: (1)

http://www.pumaracing.co.uk/POWER3.htm

give this a read......ps my last R/R was 427 fly and 360 wheels.......so that's less than 20% on a 4x4

tabetha

Read it, it's very presumptuous on thier part to assume wheels spin on all rollers, some like the one I use regularly re grip the rollers, and calibrate it often, by measuring run down losses flywheel bhp comes about, as well as crank, the difference between the two is the trans loss.
Some rollers can't be beleived anyway, as the trans losses are sent to them on a compy link or data link, that's why they are easy to fiddle.
The ones I use also have a engine dyno, and the rollers read within 1bhp of the engine dyno, so good enough for me.
Trans losses also increase with speed, pumping up tyres on a decent dyno gives no more power as trans loss, ie costa down puts it back to square one accuracy.
tabetha

botters

iTrader: (2)

not sure how much loss you get but my 4x4 is stage 3 and is 311bhp at the wheels so im guessing around 50-60 bhp loss does this sound about right?

m4tt274

iTrader: (2)

would that stand to reason that an 85bhp pinto wouldnt move with 4x4 running gear?? come on.

botters

iTrader: (2)

i think he is giving an example of how transmission losses would be the same at low power and high power not quoting exact figures mate

m4tt274

iTrader: (2)

its ok, im not stupid :L

xr2wishy

iTrader: (2)

totally, it is a percentage really.
think about it, the harder something accelerates the more resistance in a given time is occurring.

oldford

Loss on a rolling road is calculated when coasting down in neutral. Has got nothing to do with acceleration, but everything with deceleration with ZERO power applied.

Also a different gearbox has a different loss. If the engine doesn't have much horsepower, you need a gearbox with little loss.
And the lower the road speed, the lower the loss. So a 85 bhp car can move a 4x4 car, but just not as fast as a more powerful engine.