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1996 bmw M3 evo, POWER RUN

8K views 75 replies 16 participants last post by  mikim 
#1 ·
Hi, I've just booked my car in for a power run! See what BHP she's putting out!:eek:ptimist

I've not got any experience with rolling roads:shifty:. Anything i should be aware of, what should i be asking for?

Any advice would be much appreciated.:thumbsup
 
#69 · (Edited)
If there is a RR day can I bring 2 cars? 1 BMW 1 Toyota. I would like to get it dyno tested again soon.

Wheel figures are the only ones worth anything, flywheel guesses are just for pub talk. Only way to know FW BHP for sure is pop the engine out, strap it to an engine dyno and let it rip.

Dyno pack are hub dynos and there is around 2% per driven wheel less losses on a 255 section tyre, so a BMW on a dyno pack would be circa 13% at the hubs, or 17% losses at the wheels. So trans losses are even more difficult to guess from 1 machine to the next. Run down measurements are not reliable. And as the power or the engine grows the losses do not grow in a liniar fassion, so at 200bhp you may loose 15%, but 400bhp only 12%, but 12% of a far bigger number to begin with.

A dyno opperator knows you want 7565445.4bhp so can easily 'quote you happy' by altering numbers. Thats why I always quote wheel bhp for my cars. Shame the whole world cant do the same to level the plaing field. Big numbers impress the public when cars are on sale tho!
 
#73 ·
my old st170 had major mods including powerworks supercharger, performance 3000 in yeovil rr'd it at 256 bhp then on a run a week later with ffoc at west tec performance in newport it ran 282 if i remember rightly similar tempertures and both times on v power. hub dyno's are best i reckon
 
#75 ·
Rolling roads are usefull if you use the same one a lot, they can vary so much if you use different ones its pointless. They give a representation of improvements made and are a good way to take data logs if you have no logger incar. In the same week I saw 419bhp and 402bhp at the wheels (4wd) and it was the same temps and humidity, just 2 different roads. Now I have a far smaller turbo however.
 
#76 ·
If this is still going to happen, I'd love to bring the M3 up to see what's what.

For what it's worth, and it's been mentioned many times already, I too have experienced a variety of different results with my old Leon Cupra R on rolling roads. I find if there are enough people/cars there to compare against then you can kind of get an idea for how the RR is operating that day. Most people know if there car is putting out well or not, and there is always somebody there who knows exactly what their car is capable of.

One session I went to there were about 20 people, most of which were disappointed by the figures, but there were also a couple of chaps with perfect engines and their cars put out exactly what they expected. So it just goes to show how some RR's will either try to quote you happy or are set up badly. But in this case the RR was bang on.

Mik
 
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