Dynamometers/Rolling Roads

[monsport]

Had my sport on a Chassis Dynamometer at the Weekend and power output came up as 176BHP and 177.51 Lb/ft Torque which I was pleased with. But I have since been informed that these Dyna... are not as accurate as a rolling road. Anybody agree with this theory or will I get the same results from both?

[Turbo-Brown]

Is a chassis dyno one of those things that bolts to the driven hubs?

If so, I'd say it was probably more accurate than a rolling road.

However, you really can't get accurate flywheel power figures from anything that measures torque at the driven wheels as there's no absolutely accurate way of measuring transmission losses etc.

[monsport]

Yes its the Dyna Pack program which bolts onto the Hubs.

[m3wanabee]

The only thing more accurate than one of these is an engine bench dyno.

[monsport]

So would this way be better than the Rolling Road or the same. On Going arguement with a guy at work. He is Adament that the rolling Road is much more accurate.

[Karan]

i have heard some where that these hub ones are better than rollers...

also u have an auto dont u, so maybe this is better for use with an autobox and gives a better reading

i guess thats power at the wheels obviously.... that equates to about 200hp at the fly which seems right considering u have a standard cam still and an autoobox

Karan

[M5pilot]

Rememebr the car will not have any wheels on it and no tyre friction. Therefore adding approx 20-25 bhp to get flywheel figure doesnt work in this case.

On top of that your forgetting that an Auto has higher frictional losses.

Therefore to try and approximate flywheel power is hard.

Very unscientific of you Karan!

[Karan]

i do apologise....

thought drivetrain like gbox/doff counted for some power loss...

Karan

[M5pilot]

Why the sarcasm?

Unless of course what I'm saying is incorrect. Auto boxes do have more losses, there are no wheels (hence tyres), its a totally different system, its difficult to estimate flywheel power given the variables are so different.

I am making a simple point. You cannot compare figures in anyway whatso ever from different dyno especially when one is taking flywheel figures and the other is taking rear wheel HP with no wheels on it.

All I have seen is Malcoms car make 220 bhp on the bexley dyno where, on the same day, Bharats car (also auto) made 160-170 bhp.

Didnt mean to question your technical ability mate.

[Karan]

wasnt sarcasm.. i agree

[m3wanabee]

In order of true ability it goes like this/ engine dyno/ hub based dyno/ rolling road/

[monsport]

But my car isnt an auto you must have me mixed up with someone else. it was 175.4 at the fly wheel. His arguement is based around the whole wheel and tyre weight and friction on a rolling road reduces the power output compared to the dyna pack.

[Karan]

oop i thought u were monsport42 who has the 2.7 LOL

[andyp]

so did i think this , lol

[M5pilot]

Looks like we have two monsports!

[320Touring]

this guy at puma motorsport provides some interesting onfo when going to a rolling road

http://www.pumaracing.co.uk/rrvisit2.htm

[monsport]

I was thinking i was being mistaken for somebody else. 2.7 wouldnt mind that at all...

[Jos]

A friend of mine was at a Dyno Day last week (Vauxhall nut..), the bloke there measured drivetrain loss by setting the car at 3000rpm and dipping the clutch. The 'box of tricks' then times how long it takes for the wheels to come to a stop. It then somehow calulates out the drivetrain loss from that.

From 5 cars that were stock the calculated flywheel HP was within 2-3hp of the book figures, the readings were all high but it was freezing cold (-2C) during testing, which could account for it.

Just my 2c

[Turbo-Brown]

Aah, that's a coast-down test. It's better than just adding some arbitraty figure to the wheel figure by a long shot!

Still, it's never gonna be totally accurate to quote fly figures for something measured miles away from the engine

Shame that the wheel figures never sound quite so impressive!

[MONSPORT42]

Yeh, I discovered there was two of us the other day when I got a PM for monsport (lower case). Since the Forum change mine's in caps and of course has the all important 42 (The answer to all the questions in the universe - Hitchhiker's Guide to the Galaxy) There's arrogance for you!!!!
Last print-out at Bexley after MAF remap at the end of a 3 hour session on the the R/R - very hot. Had more work done since then and a new gearbox the old one was slipping so should be showing higher output now. You can see the gearbox limiter cut in before the ECU rev limiter - there was more to go.