rolling road results

[avants2turbo]

Can somebody help me, ive recently had my s2 avant on the rolling road at QST, and it was done almost exactly 3 years earlier, on the same rolling road.

Im having some trouble understanding the differences between the tow sessions.

The thing i dont understand is the Rotating mass,

on the one done 3 years ago its says the rotational mass is 250kg

and on the one done a couple of weeks ago its about 670kg

what is being measured? the weight of the rotating mass on each corner, total rotating mass all four corners?

what difference does the 2 different rotating masses make to the results?


I ask because the car has done 20k miles between the two runs, and the BHP is almost identical (283bhp first run (3 years ago), and 286bhp second run(2 weeks ago))

but the torque figure is very different (403NM first run, 381NM second run)

and the torque curve is much higher on the first run for longer on the first run

any info would be greatly appreciated.....

[S2central.net]

Some numbers seem a bit bonkers here... Can you post up images of the plots you have.

The rolling roads attempt to measure 'transmission loss' thru drivetrain whilst on the rollers.

The MOST important figures you want from the rollers are what is measured AT THE WHEELS... Some rollers and operators use wacky techniques to inflate the transmission loss figures so that they can claim higher flywheel power than is truly accurate.

Different tyre pressures, heavier wheels and other things can affect the loss estimate - you are best doing ALL runs on the same wheels/tyres/pressures and also in the same gear - 4th is best IMO.

Opinions differ on how much transmission loss is normal for a torsen equipped quattro, but a rule of thumb for ~25% is pretty good but even with that you can get different results.

If you measure say 210bhp at the wheels you could divide by (100%-25%) to get flywheel power of 280bhp
Another way to do it is to take the wheel figure (210) and add 25% of that to get a flywheel figure of 262bhp.

Either way - the figure at the wheels is the most important one when looking for differences between various setups on the same car on the same rollers.

[Rusty]

You need to compare power at the wheels really to decide if anything's wrong.

The differences sound fine to me, the peak torque on a turbo is a bit peaky an depends on many factors. Petrol used, air temp. small boost leak, weaker plugs... so many differences. The fact that there's more power there indicates that something might have changed a little.

Best check all the small bore hoses as these are usually the cause of niggly little leaks rather than overboost triggerring.

i always change plugs every 10k and run on Tesco 99 as it's rocket fuel!

[DarrenM]

Im the same, i was wondering what the crack was with Rotating mass (and Drag power). Got mine dynoed last friday and the dreaded boost problems over 5K came back to bite me on the arris..

what is the drag power? Figures attached..

[EspenW]

Drag power is power lost to rolling resistance and losses in the drivetrain.
MAHA dynos use advanced algorithms to calculate this, and they always come up with seemingly nutcase numbers for drivetrain loss. 35% in this example.

[avants2turbo]

Im the same, i was wondering what the crack was with Rotating mass (and Drag power). Got mine dynoed last friday and the dreaded boost problems over 5K came back to bite me on the arris..

what is the drag power? Figures attached..

whats the spec of your engine mate?
apart from the dip at 5k it looks good and healthy....

where your dyno had the rotating mass as 310kg and the number below mine had approx double all the figures aboutt 650kg??

[A80Avant]

story of my maha dyno is already discussed here...

[avants2turbo]

story of my maha dyno is already discussed here...

huh?

[A80Avant]

if you search a thread called: GT3071R dyno results you will read about the differences a maha dyno has from a rototest hub dyno has and people say generally about them.Although i cannot say i like maha because it gives odd readings,most tuners seem to like it.Mihnea is one as well.All say that unless there is good cooling fan,you cannot get good results.

[DarrenM]

whats the spec of your engine mate?
apart from the dip at 5k it looks good and healthy....

where your dyno had the rotating mass as 310kg and the number below mine had approx double all the figures aboutt 650kg??

Engine wise,more or less standard with RS2 turbo & homefry. Wanted somewhere between 300-315bhp with a decent torque but for relatively little £££. Is also running 3" turboback system and metal head gasket which both needed sorting earlier in year. For the sake of £300.00 odd quid for the turbo (plus fitting obviously) gives loads more grunt altho bit more laggy.

Will uprate injectors,IC, map etc later in year but not going mad on power as got other things swallowing up the money