john banks

EDIT - Morning Theo!!

It seems that the loading on the rollers can have a potentially large effect on the "transmission losses" - Sam's Evo 7 on one run 140 bhp losses, on another with different loading 68 bhp, but similar "power at wheels" within 2-4%, but around 20% errors on the "flywheel" power on the same RR with the same car. There are obvious difficulties in comparing cars with different intercoolers and gear ratios. Temperatures quoted from an inlet temp probe also seem to vary wildly, and the correction factor seems suspect.

Apparently there are tricks with bench dynos too? Are there loading, temperature, reproducing realistic intake/exhaust effects, as well as how many ancillaries attached to the engine and the loading on them leading to variable losses? Just some ways I could guess might allow you to get wildly different results.

Is it fair to say we are picking our least inaccurate version of a very imprecise system or am I being overly cynical?

Whatever, are the errors on rolling roads potentially so great that it is very difficult to tell anything at all significant from the sort of lo-po mods I tend to do?

Any why the fascination with "dyno-tuning" when they are such an odd way of reproducing realistic airflows and load? I am not a mapper, but it strikes me as a bit of an odd way to produce a map? Perhaps we can't run at 7200-8200 RPM in 4 or 5th gear but just because you can get it up there safely on a dyno does it mean that the map you produce is carrying the sort of accuracy that the phrase "dyno-tuned" would evoke in most customers' minds? Or have I missed something massive here? (quite likely )

[Edited by john banks - 3/2/2002 9:52:18 AM]

alanjack

At Well Lane, would the results be from the wheels?

alanjack

Surely someone must know!!

scooby_si

er i guess it's at the flywheel if it's upward of 200bhp in a scoob im just guessing having looked at the stats from dyno/scoobynet as per http://dyno.scoobynet.co.uk/PEindex/uk.htm
HOpe that's of sum use?
Si

RichardPON

It should be an @ wheels figure, cos that's the actual measurement that comes off the rollers. The flywheel figure is "calculated" as an addition of the @ wheels figure and your supposed transmission loss.

The rr company should give you both figures, but the @ wheels figure is the only one that matters. Only true (ish) flywheel figure is on an engine dyno.

Cheers.

R19KET

RichardPon,

So do you think that the "at the wheels" figures of a RR, are more accurate than the crank figure given by an engine dyno ?

Mark.

EvilBevel

Mark, that's a trick question

The short answer is ... they are both inaccurate, but hopefully the software will calculate/compensate correctly depending on the load/gear/temps, so the flywheel figure in the end will be the least inaccurate.



Theo

RichardPON

Mark,

See where you going with that one! Trick question of sorts!

Of course the dyno figure is more accurate, but ancillaries aren't catered for on the dyno, in the same way that they are in situ in the car.

Was just pointing out that flywheel figures from a rr are notoriously innacurate, cos I've never seen a machine that accurately measures transmission loss.

R19KET

Guy's,

It wasn't a "trick" question.

Richard you're right, you don't run the ancillaries on an engine dyno, but they account for such little losses, that it's neither here, nor there.

What I find interesting, is that ATW's figures vary dramatically from RR, to RR, too, where theoretically, they should be the same.

As an example, in the USA, the average ATW's figure for an '02 car, with stock TD04, 12psi, exhaust, and Unichip, is "220bhp" (yes, ATW's)and cars running a VF23 (or similar) at 18psi, are seeing circa 270bhp ATW's. Try and get this in the UK !!!!!!

It's nothing to do with mapping ability, it's a software issue, but which is right ?

Who knows how accurate even engine dyno's are, but it will be interesting to compare my engine dyno figures, to what I get on a RR.

By the way, RR figures will always be given ATC, unless you ask for ATW's, because that's what people want to see.......

Mark.

harvey

iTrader: (48)

Alanjack : To answer your original thread : Ask Well Lane. They have always been helpful. The graphs I have from them all show flywheel BHP. I am not sure but the large meter near the screen may show PAW during the run up but at the end of the run the computer calculates the losses & produces the torque & power curve at the flywheel. I think a dynomometer is a more accurate means of measuring flywheel power.