Understanding rolling road results

[kevin316i]

I had my car on a rolling road on Saturday, and was pleased overall with its performance, but had some questions about the results that you guys might be able to offer an opinion on:

Car : E30 316i (M40) non-cat
Mods : K&N panel filter
Engine has approx 60,000 miles done.

Results : 103 bhp, 140.1 Nm torque
Handbook quoted figures : 102bhp, 143 Nm torque

The operator commented that the car was running a little lean. I had the CO adjusted after Christmas as it when it was checked it was supposed to be running a little rich.

Will the engine running slightly lean explain the slight dop in expected torque? Is it just a case of getting the CO adjusted again?

Thanks,
Kevin.

[astondg]

Is a rolling road very similar or the same thing as a dyno? I mean it measures power at the wheels? The handbook figures should be at the flywheel so if you are getting 103BHP at the wheels that is much more than the standard car.

Otherwise maybe the rolling road results were corrected to "at the flywheel" power in which case they may not be completely accurate so I wouldn't be worried about the 2.9Nm difference in torque.

Also engines can be different by probably that much. Your's might just have a little bit more powr and a little bit less torque, that difference isn't much. I think the first idea is more likely though.

Aston

[kevin316i]

The figures are the calculated 'at the flywheel' results. Can't remember the bhp figure for at the wheels - someting like 74bhp I think.

[320Touring]

a lot of rolling roads factor in too much power loss due to the drive train!

tbh, a loss of about 17% is normal in RWD cars, so going on the 74bhp at the wheels, i'd expect 74x1.17= 86.58bhp at the flywheel.-sounds a bit low

check the print out to see if he has set the % loss very high?!?

based on the handbook 102bhp at the fly translates to 84.66bhp at the wheels (102x0.83).
this sounds a bit more like it-if you have significantly lower at the wheels power then the rolling road dude may be taking the pi$$ (probably 80bhp or above is ok)

hope that helps you make sense of the figures...

[astondg]

Power loss also depends on the type of transmission, an automatic would loose more.

It's still hard to tell though, I have heard poeple say the losses could be anything from 10% to 25% for a RWD.

You'll probably have to wait until someone else who has had a 316i on a dyno replies.

EDIT: So if the person that did it used a decent loss % to get the flywheel figures then yours sounds ok. The small difference could be a slightly incorrect % or something like that.

Aston

[kevin316i]

There was an E36 316i on the rolling road on Saturday, he got 102bhp. Again, standard car, but I think it has a later engine than the M40.

[Demlotcrew]

The K&N filter will make the car run lean.

Andrew

[kevin316i]

So getting the fuel-air mix a bit richer will fix this OK? I wonder is it worth buying a home CO analyser, like the type sold by Gunsons?