rolling road at international

[Guest themiserymachine]

go on , you know you want to tell !!

what did your car do ?

ill start with mine - sal464x tr7 v8

did a respectable 174 bhp at back wheels.

[malcolm]

Were they giving power 'the the wheels' this time?  For some reason the mobile rolling road guys at Mallory Park were giving out flywheel figures.  Not sure how (or why?) they were doing it.

 

Malcolm.

[Guest schofieldtr]

hi all

174 was only 4700rpm so pretty good i think

surely the yellow beastie wheels are to fat for the road.

when you race her please let us all know.

i did hear about a v8 that took the dial off the clock.is that KEH  then??

did anyone see bob mortimers car on the rolling road after it had been re tuned did it do better than the original bhp it did first time round.

also did you see john,s car with the tomcat engine.

171 bhp.it turns out he owned sal back in the late eighties when it was still persian blue and 2lts.

if anyone as a contact number or email address for him can you please let me know it as i would love to see the photos he took of my car as his together.

graham

[malcolm]

I got a flywheel figure at Mallory Park of 210bhp at a miserly 4600rpm.  This bodes well for my hoped for approx 250bhp as the car pushes hard to 6000rpm on the track.  According to info I've found on the web this equates to about 175bhp at the wheels (and 250bhp is approx 210bhp at the wheels, which is what KEH was doing).

 

Malcolm.

[Andy Moltu]

I suspect the figures from the one at the international were a tad optimistic.

It had a bog standard 5 putting out 125 at the wheels - given that they were good for about 137 bhp (DIN) at the flywheel in perfect conditions makes 125 at the wheels seem unlikely.

 

When rolling roads quote flywheel figures it gets even more muddled using calculations from the overrun to work out what power is estimated to be lost in the transmission,

 

There are huge variations in rolling roads so it's hard to compare figures from one to another.

[martynharrison]

You surprise me. I know I don't trust the flywheel figures because, well, they're just modified directly with the operator controls. You can literally have the same car go from 100 BHP to 800 BHP if the operator wants it. And sometimes they do, if you just spent a grand on a hoogie cam you want them to find they have, indeed, improved your power output.

 

But the figures "at the wheel" should be being measured directly by a device that should be pretty much accurate, otherwise why bother at all?

[jonlar]

I'm not an engineer, but have always understood that genuine engine flywheel BHP figures with no transmission attached (so no losses) taken with a dynamometer are correct and accurate.   The rolling road converted figures cannot be calculated really accurately, because of the variable losses from box to box, although the figures for "at the wheel" are accurate.    Am I correct?   Any engineers out there with definitive answers?

[martynharrison]

Well I can say that engine on the bench figures can be measured directly, and car with wheels on the rollers can be measured directly, but when the car is on the rolling road and you get BHP at the flywheel, that can only be inferred.

 

And I know how that can be done, i.e. by software. It's potentially accurate but just as easily manipulated in software.

 

But I have to admit, having machinery that can give accurate figures when measuring directly and has been set *not to* is a bit non-engineer.

[jothecat]

[]i did hear about a v8 that took the dial off the clock.

 

Well this was my 1st international & 1st rolling rd. FVA430W was the 3rd car on the rolling road and it did exceed the maximum on the dial. If you extrapolate the curve on the print it would have got to 248-250 bhp. The tester said it had "some power".

[Andy Moltu]

There is always going to be an element of variability with rolling roads.

 

How are they calibrated?

How are they adjusted?

When was it calibrated?

What is their accuracy?

In what range was it built to read accurately?

Does it compensate for factors such as ambient temperature?

 

Unless you can bolt your engine directly to a dyno (not practical for most car owners) the figure that's relevant is the power at the wheels rather than the "flywheel power measured at the wheels" which is at worst a guess and at best a limited quality calculation.

 

In terms of assessing the benefits of various engine tuning effects it's best to use the same rolling road to aim for a more valid comparison.