Went to Rolling Road Yesterday for initial setup after run in and got 250 at wheels which i'm happy with de-cat,stainless,induction kit

 

At the wheels? are you sure?

 

That's what I thought.

 

thats the graph i got my brother took the car i could'nt get there 249.8bhp

 

That would be somewhere around 330bhp at the flywheel.

 

That's at the flywheel..........................

 

Mine was 258bhp at the wheels, 301bhp at the fly, courtesy of Dastek, recommended by Andy F.

 

wow, a sensible tranny loss figure you are aware you can add up to 23% for great pub figures aren't you?

 

Wow Andy, that's a tranny loss of between 14% to 16.5% depending on whether you take it from 301 or add it to 258..!

If it actually produced 258 at the wheels, IMHO it would indicate a fly output of more like 316 bhp, which for your mods would make far more sense..!

Why do some people not believe tranny losses >20% are normal for the impreza..! Do they know what the average tranny loss for FWD and RWD are I wonder..?

Something like this, FWD ~13 to 15% and RWD 15 to 19% depending on the design of diffs/gearbox etc..! With this in mind answer this, how can a relatively antiquated AWD system like the impreza, with double the diffs etc have lower tranny losses than a simpler FWD drive-train..?

 

cheers not too impressed with figures now

 

Cheers Jase. I like that figure - I have to say it feels plently quick enough for me !

258bhp was the measured figured - the 301bhp was a calculation by the programme.

So what percentage transmission losses did you use for Scoobs to calculate that ?

Andy

 

The car sits much higher on the rollers of a Dastek and hence the rolling drag from tyre distortion is considerably less than say a MAHA set up.

We have a MAHA and Dastek within a few miles of each other, they typically show within 15bhp difference of power at flywheel figures on a mid 300bhp car but the wheel power can differ by 30-50bhp. Its just due to the design of the dyno, they will have different losses.
The dyno dynamics rolling roads such as at TEG and Scoobyclinic don't measure losses, they just add a pre determined value to the power at wheels figure, so if you have wide tyres or run them at lower pressure you will appear to have lower bhp.
For a good pub talk figure on a DD rolling road, fit your narrowest tyres and pump them up to 50 psi, also run low viscosity oil in your transmission and fully warm it up before the run. Simple way to gain 20-30 bhp at the flywheel !!

Andy

 

Cheers for your insight Andy.

Does this mean that the Dastek RR does measure the losses ? I had assumed the only measured figure was the "at the wheel" figure, and that with all rolling roads the "at the fly" figure that everyone quotes is simply a calculation based on a predetermined percentage used within the programme to allow for transmission losses ?

 

Andy I have always been a bit interested as to the reason Power Station (and some others) seem to always show 30% or so losses, makes a nonsense of sticking to paw figs I think.

Any thoughts?

Something thats been bugging me as certain DD operators claim this rolling road is the "most accurate". Accuracy being the wrong description of course as that implies correctness which no rolling road can claim.

I use 22% as a rough cut loss which I think is reasonable, Shoot 44 on a DD rollling road uses 21.8% (ish)

Bob

 

That's very interesting, Andy. I had an argument/discussion on another forum when I posted the graph of my Octavias results. On a MAHA dyno it showed 179 bhp at the wheels, with 233 bhp at the fly, with a Drag output of 54 bhp. The other guy said that the dyno must have been fiddled as 54 bhp was too much for FWD transmission losses. My argument was that the 54 bhp wasn't just transmission losses!

We eventually agreed to disagree...............

 

Bob

I believe its mainly due to the roller diameter, surface finish and pitch. On a MAHA such as Power station the cars tend to sit down into the rollers, the tyre then has a combination vertical load and horizontal clamping forces on it as it 'wedges' itself between the rollers.
The rundown losses are also extrapolated upwards on the MAHA from above the point at which the overrun measuring starts, this is why you don't see the full graph until it extrapolates the load and adds it to the paw curve at the end of the rundown.
It may be that the different designs also calculate windage losses etc in a different way.
If we mention dastek enough times in this thread perhaps Gerry will pick up on it and clarify further.

Andy

 

The load on the rollers during the rundown is used in a calculation to generate a drag or loss curve which is added to the measured figure (wheel) to give a flywheel power. It is more accurate in my opinion than just a 'one fits all' style addition as used by some other rollers.

Andy

 

Many thanks Andy.

Andy Mc

 

Me too, Andy. Confirms my ar$e dyno readings

I didn't really think that Scotlands most respected VAG tuner was fiddling his dyno readings

 

 

Apologies to be sort-of hikacking this thread, but can the RR guru's help explain the various figures on a PowerStation printout? My printout shows:

Corrected Power* (358.9)
Engine Power (342.1)
Wheel Power (228.5)
Drag Power (113.6)

*Correction according to DIN 70020

I can see that drag power + wheel power = Engine Power, at 342.1 but the corrected figure increases this to nearly 360bhp. What is the correction for?

There would appear to be an approx 35% correction factor between wheel and corrected, which seems very high.

View my scooby for the printout.