Ambient Temps. on the rollers?

[Stealth Racing 5]

Hi Guys

Thanks to all who attended the RR shoot-out last Sunday, was a good day and a good turnout.

First of all on the Subject of intake temps, VR6 engines are very heat sensitive and can loose up to 10bhp between a cool run on the rollers and a hot run.

The intake temp figures we put in to our RR software for horsepower correction are as follows.. Start temp set at ambient and end temp about 3-5 degrees higher, this takes into account the intake air temp rise during the power run. Rolling road testing is not carried out in a totally controlled situation to achieve 100% accurate figures, close or very near close is the best we can hope to achieve.

Force inducted cars by their nature create much higher intake temps, on these cars we generally monitor the actual temp through the diagnostic port during the run then input that figure into our RR software.

Flywheel BHP vs Wheel BHP..

I read the Puma racing coast down losses a few years back (shortly after purchasing our dyno) interesting read and I agree with most of what is written..

BUT

Since then I?ve had 3 yrs + dyno experience on VAG cars and this is what I have found.

Totally standard Golf 2 16V, VAG say 139bhp Stealth measure nearer 145bhp, we all know VAG engines just get better with age.

Totally standard VR6 OBD 1 VAG say 173bhp: Stealth measure under 180bhp (but high 170?s)

Totally standard VR6 OBD 2: Stealth measure 185bhp-192 bhp. VW quoted BHP same as OBD1 but you only have to drive one to realise straight away the OBD2 is quicker.

Corrado VR6: VAG say 193bhp, Stealth measure 190bhp-195bhp

There is always the exception to the rule, I?ve seen some standard cars produce way over standard spec BHP, maybe a Monday morning engine? I know I used to have a Friday afternoon 16V Golf, shit power horrible to drive no matter what I did to it tuning wise.

Note: All of the above are Flywheel figures??

The above figures satisfy me that our rollers produce a reasonably accurate flywheel figure when compared to what VAG state, if I did not think that this was the case then I would change it.

OK, now down to power at the wheels. I?ve had long drawn out conversations with some customers about this over the years and one guy in particular, he was adamant he was right and the figures I gave him were wrong. (he kept referring to what he read on Puma Racing) His argument was that only a power at the wheels figure was the one which had any real meaning, anything else was crap!!

This prompted me to do some testing of my own, and in front of said customer..

Figures I am quoting below are simplified for ease, (mainly because I can?t remember the actuals). You should get the idea though

Took a car and carried out power test.

Wheel bhp: 100bhp.

Transmission loss 40bhp

Flywheel figure 140bhp

Took same car and put tracking out by 6mm then back on rollers for power test.

Wheel BHP 95bhp

Transmission loss 45bhp

Flywheel figure 140bhp

From this my assumption is that no matter how inaccurate a ?Rolling Road Flywheel? figure may be, in my opinion it can calculate any discrepancies in the transmission losses therefore showing a repeatable flywheel figure. There are lots of things that can affect losses, Wheels/tyres, brake disc weight, driveshafts, etc.. change any of these and you will affect your power at the wheels bhp, if however measured on our rolling road then your flywheel figure will remain the same but will be calculated differently..

On RR days there is one thing that you all suffer from, that?s high-ish Transmission loss figures.. Why???? Most of you have all your bonnets open trying to get your engines to cool down and get rid of that dreaded heat soak, and why not, everyone wants to see good power from their car.. I then get the car on the rollers bring engine up to a safe temp to carry out power run but your gear oil is stone cold and very thick, just another contributing factor to a lower power at the wheels figure, my dyno measures this though and adds this higher loss to the power measured at the wheels and gives me a repeatable flywheel figure.

I?m happy with the way our Dyno works and with the figures it gives me at the flywheel, (my preferred way of measuring) I feel the accuracy is close enough to be comparable with what VAG say their cars do. Like I said I?m happy but I would change it if it were not the case..

Hope this answers some questions for you?

Although I?m really crap at explaining things so you?re probably more confused now than before?

Sorry to go on

Regards

Vince

[kobi 0]

this man knows his shit. cant really ask for any more explanations than that.

I wasnt at the RR day but most if not all of you have decent figures (i'm referring to your cars read outs of course!).

When we have a man like in the know like Vince amongst us.... who needs VW dealers?!

Interesting read Vince, nice one. I can go to sleep now.

[Eat this 2]

i got averege power at wheels but great flywheel bhp i do agree with vinces explanation but i also agree with pumaracing that corrected flywheel bhp will never be 100% accurate it may be that my engine put out 198 bhp then again it may not have il never know for SURE without usin an engine dyno but the power at wheels is actually measured power which assuming the rollers r calibrated (goin by everythin iv heard about vince they are) then the only garanteed accurate figure is the wheel figure beleive me id love to go from the flywheel figures not countin fi and r32 cars i was 3rd!!!! and the 2 tha beat me AND quite a few who didnt have schricks and have been mapped/chipped but i just cant 100% trust the corrected figures and id rather rely on a deffinate figure than a maybe maybe not figure this is in no way an attack on vince i just cant trust a measurement system thats fundamentally flawed i do think/hope my engine puts out around 200 bhp though

[ Edited Wed Nov 03 2004, 07:56AM ]

[ Edited Wed Nov 03 2004, 07:56AM ]

[anorak 0]

Thanks for the explanation, Vince. I'm far happier with the fly figures now. I did expect some variation due to tracking and tyres (just not a range from 30 to 58bhp).

I'd better add a tracking and bearing check to my booking with you!

[Pittuf 0]

got my tracking done yesterday....I wanna go again :-p

[Valver 0]

Vince is da man!!

Can't think of many tuners that would take the time out to come on here to share their wealth of experience/knowledge and explain things in that much detail!

Well done imo.

8)

[antera309 3]

True words spoken by Vince there. Transmission loss in particular depends on so many things. Tyre type & pressure, camber/caster/toe settings, condition of wheel bearings & gearbox, gearbox oil type and temperature, the list is endless.

My car lost a whole 11bhp at the wheels compared to it's last run, just by the tracking being out...

[six appeal 53]

The Main man as far as I'm concerned in the world of VR tuning has spoken! Here endeth the lesson!

Thanks for taking the time out to come on here Vince, and big thanks for the smooth and efficient running of the RR day! Stealth just gets better everytime I visit!

[anorak 0]

Absolutely - I'm lucky if I can get my local grease monkies to answer the phone!

Whatever the reasons for power loss, I suppose the bottom line is that the flywheel power is a measure of how strong the engine is and the wheel bhp will tell you which car is going to be quickest on the road. (Weight being equal).

Mine's down on both counts so Vince has got his work cut out