Ok having a bit of an arguement with someone bout power figures for rolling roads. In general the figures are what the car is putting out at the wheels aren't they? he seems to think they are flywheel figures? who is correct?

 

Wheel power is all that can be measured.

Easy way to end your argument. Ask him if he did a run with his brakes hard on, would it show a lower figure? Yes?

Cant be flywheel power then can it? End of discussion.

 

wow im actually corrrect for once cheers stu!

ok- now i'm onto the next stage of the arguement, an Escort RS turbo would be putting out in the region of 160-170bhp (at the wheels) with an exhaust a chip, -31 actuator (running 1 bar boost) and an air filter. oh and the car has also been setup properly.

 

No. The general figures quoted everywhere are flywheel.

 

This is where the confusion arrises..

It actually "Measures" wheelpower, and then it measures wheel "resistance" on costdown to calculate a flywheel figure.

So quoted power is at the flywheel normally, but only the wheel power is actually accurate really.

 

i'm getting these figures from the likes of the dyno shootout in fast ford. I realise that all cars differ depending on what mods are done and who did them etc, but going buy the dyno shootouts, which i take are at the wheels figures? 160-170 bhp is a realistic figure from the items listed? if not, does anyone know what a car of this spec should be putting out at the wheels?

 

RR for @ wheels figures, engine dyno for flywheel fig's. Far too many tricks/variables for an accurate flywheel figure from a rolling road.

Nearly all mag figures are flywheel fig's (such as they are).

 

now im a bit confusted

ok so to lay it out simply if an rs tubo with an exhaust a chip, -31 actuator (running 1 bar boost) and an air filter was put on a rolling road what would it put out?

i take it that then the ones in all those rolling road shootouts in fast ford/performance ford are flywheel figures then? even tho they were on a rolling road?

 

Pretty much, as punters prefer the higher figure

An RST of the spec you describe would probably give 175-190 'guesstimated' @flywheel figure on a rolling road, depending which RR used.....

 

As Stu say, the only accurate figure from a RR is the @ wheels figure.

The 'estimated' flywheel figures are usually the figures quoted though because the number is bigger and more impressive (And most 4x4 owners would cry quoting at wheels figures )

 

GurnE, 226.2bhp @ the wheels / 371lb-ft torque And I'm happy with that on the road

 

i'm not really fussed on the power figure of my car, just how it goes on the road. This whole post has come about from someone not believing me that i sat with an e36 m3. My car has chip, -31 actuator, exhaust, piper X, Grs intercooler, piper 285t2 cam. Now the car is not running right at all and is the same speed as one with the mods as described earlier. But a t the end of the day i even have the race on video! but hes trying to say that the m3 has 321 bhp, but surely that is at the flywheel as well? also those things weigh like 500kg more than an rs!

 

I would say that a car with that spec would be a maximum of 175bhp (at the Flywheel), but more likely 165-170. Main restriction IMO is the Intercooler. 1 Bar of boost is just about too much for a standard IC.

 

ok then roughly how much does an rs loose in the transmission?

 

You are right about the Power to Weight theory. That 500kg difference accounts for alot. The addition of a GRS IC and a T2 cam would possibly bring the car close to 190-200bhp (Flywheel). Next restriction is the Turbo.

Is it not running right since the race?? How many miles has it done?

The BMW power figure is indeed a figure measured at the engine. Every manufacturer seems to differ on the figures they quote in terms of accuracy. E.G. Mitsubishi quote 276bhp for the EVO 6, because by law they have to, but they actually make nearer 290-300.

 

30-35bhp. Depends to ambient temps (which affect the temp of the gearbox oil etc). Also if a car is run several times, the losses will decrease. This will reflect in the Engine Power that the RR Run produces (will probably be less because Engine Power = Wheel Power + Transmission Losses).

Here is another example. Take a look at the Norris Designs Evo and also the RC Developements Evo. They both quote figures around and in excess of 800bhp. But they have 250-300bhp Transmission loss and around 600bhp at the wheels. How does that happen??!! What happens when a cars horsepower increases that affects the resistance of the transmission?? Always baffled me that one.

 

"250-300bhp and theres what 1.21? kilowats in 1bhp.
Looking at an electric heater that puts out 3kilowats there hot.

over 200kilowats sureley would melt the transmition like chocolate.

 

Exactly.

So what does that tell us?? It tells ME that the Norris EVO and the RC Developments EVO are 600 (or whatever) bhp at the wheels, but NOT 800-900 at the engine (until the figures are verified on an Engine Dyno that is).

 

 

the car has never been running right. it is yet to be setup and is running a rich as it possibly can. But it is booked in for the start of next month to get sorted so it should be ok. Its only got 40k on it as well.