Trap2Terrorist

iTrader: (3)

I have recently put my car on another rolling road and have my power figures on a print out. I have noticed that there are a number of bhp figures on the sheet.

When people talk about "my car's got xxxbhp", are they taling about "Engine power" or "Corrected power"?

(I realise there is also "Wheel power" after transmission loss).

For example my current figures are:

Corrected power - 261.2bhp
Engine power - 264.2bhp
Wheel power - 165.7bhp

Thanks

ru'

Normally they'll take the highest figure, i.e. the dyno measures hp at the wheels, then 'measures' transmission loss on the overrun and uses this to work out hp at the flywheel (which is what manufacturers quote).

This may then be corrected for ambient temperature etc. to give the corrected figure you have.

If we add to this the apparent variability of different dynos (i.e. if you post your power figure, someone is bound to post "oh, you didn't get it done at xyz company? Their dyno overreads by 50%" or something helpful!

ps out of interest, what car is it, what mods (if any) and what's your peak torque figure/rpm?

Dracoro

That's 38% transmission losses

Trap2Terrorist

iTrader: (3)

Hi RU'

It's a bugeye WRX with Magnex 6x4 oval bb, magnex decat centre pipe, green cotton panel filter, ecutek remap at Powerstation.

I've also had a Walbro 255 fuel pump fitted as a precaution.

I'm getting 348.8 Nm (257.26 lb/ft) at 3840 rpm's, which I'm pretty happy with.

mg driver

100 bhp loss through transmission down to only 165 at the wheels ,,is that right my front drive car only makes the power of a standard wrx and yet its 170 + at the wheels.

Mitchy260

Nothing strange about your losses at all!

Scoobies are renound for losing lots of power through the transmission.

See here.....

http://dyno.scoobynet.co.uk/PEindex/jap.htm

Trap2Terrorist

iTrader: (3)

Correct, nothing strange about it at all. That's what you get for having AWD, everything has pro's and con's.

Increased traction, increased transmission loss.

ru'

Good figures, and nice looking motor!

Trap2Terrorist

iTrader: (3)

Cheers!

jasonius

iTrader: (1)

AWD tranny losses are always way over estimated on a RR. IIRC due to the fact that the tyres on all four wheels are contacting in two areas (double rollers) instead of one (as on the road) = twice the friction = twice the drag. You get this on FWD/RWD also but only on two wheels of course..!

Typically scoob tranny losses (newage) ~ 20%.

Andy F is quite clued up on this subject if you need varification..!

jasonius

iTrader: (1)

Trap2:

Are those Tarmac 18's on your scoob..?

Aztec Performance Ltd

iTrader: (234)

Mine had 21% transmission losses on DynoDynamics rollers.
Yours is showing est 40% losses?

flat4_ire

walbro fitted for precaution?
thought the standard one would be fine with those mods man

explore

BIT CONFUSED mine got 268 at the fly and around 223 at the wheels with 250lb of torque

scoobyboy1

iTrader: (16)

How much power did your car make BOB'5.

Aztec Performance Ltd

iTrader: (234)

340/340

Aztec Performance Ltd

iTrader: (234)

at fly.

paulcornwall

Seems alot of loss @ 38%, are you sure thats right?

LitchfieldImports

Pinched from a similar thread, Rich at Powerstation said:

The flywheel HP figure is the sum of the HP "@ the wheels" and the drag measured during coastdown. The Coastdown drag curve is exponential therefore the drag is NOT a fixed percentage. The wheels figure is meaningless without some form of drag measurement. All these factors affect the power @ the wheels. Tyre type/size/pressure/temperature, gear/diff ratio, gear oil viscosity and gear selected. The gear ratios and gear selected have the most dramatic affect because, simply put, the greater the speed the more the drag hence the lower the wheels HP figure.

The greater the speed the higher the drag figure and the lower the "@ the wheels" figure.

It should be noted that the drag figure measured on a rolling road is far greater than you would experience on the road as on the dyno the car sits on 8 small circumference rollers which deform the tyre. The drag measured is true though, you would have a lower drag and a higher "at the wheels" figure on the public highway.
I hope the explains some of the variations seen between different cars.

I think this is what confuses people especially if they compare a dyno such Powerstation’s MAHA to a Dyno Dynamics setup used by people like Scoobyclinc. Powerstation’s is designed to measure power at the flywheel, Scoobyclinics is designed to measured power at the wheels. Both would say they are accurate at what they do but trying to compare two different approaches is very difficult

Iain

wrc350bhp

what about same dyno different company should they be about the same? mine wernt

Trap2Terrorist

iTrader: (3)

jasonius - Yes, Rota GTA 18's (newer version of Tarmac II's) in Gunmetal

flat4_ire - Walbro fitted as precaution on recommendation of Powerstation, (not done by them though). The standard WRX pump is not as good as a Walbro so I thought, better safe than sorry.

Litchfieldimports - I had my mapping and RR done by Powerstation and they certainly know what they're doing. I guess the "Engine power" figure is the right one, ie. 264.2 bhp.

LitchfieldImports

WRC350 there could be a number of factors between to two like temp, fansize, gear used etc. You have to feel a little sorry for the dyno owner as if they give reading under expection it must be a problem with there (expensive) machine and if they give a high figure they are branded optimistic.
I've had many cars on dynos over the years and the only thing that matters now is that results are consistant for mapping and power fiqures we quote.

Iain

Trap2Terrorist

iTrader: (3)

I agree, and Rich at Powerstation was confident that even though the bhp figures might change depending on ambient air temp, etc. the torque figure should stay pretty much the same from one RR test to another (on the same machine). And he was right.

p.s. Powerstation always doing the RR in 4th gear.

rentonone

iTrader: (1)

wat was your intake air temperature mate?

Nick Read

Basically, the bottom line is all RR results should be treated with caution apart from one basic measure - power or torque at the wheels. If you always focus on 'at the wheels' measurements then you always have an untainted raw measurement with which to compare different mods you might do or across different rolling roads. And against different cars if that's your thing, e.g. if your Scoob makes 170 bhp at the wheels and another one (same model) makes 200bhp at the wheels, it's not exactly rocket science which one should be faster under any conditions. And you know someone's bull****ting if the two cars perform the same. Concentrate on how fast it is to drive and forget the RR bull****. IMHO. Not saying that RRs don't have their uses, of course they do. But this idea that with just a one-off reading you can tell whether your particular car is running well or not...it's optimistic. RRs should be used as a diagnostic tool for 'before and after' work, or to compare two similar cars, not for standalone power runs. I'm sure some people in the RR business would agree and some would differ. I'm just calling it how I see it, and I've watched hundreds of different cars on dozens of different rolling roads in all kinds of different conditions.

If you're the sort of person who really wants to know how their car is performing or how it compares to others, or whether your mods are working etc etc, the best thing to get into is quarter miling. You'll never look back. All the pub (and forum) talk in the world makes absolutely sod all difference once you're sitting there on the line ready to do battle. As the saying goes, 'Once the flag drops, the bull**** stops.' When you've got your launches and gearchanges right you'll see very near to the true potential of your Scoob and if it's consistently running the quarter quicker than your mate's '300bhp' Scoob then you've got the faster car, simple as that.

Trap2Terrorist

iTrader: (3)

Not sure, I don't have the print0ut with me at the moment.

14.4C seems to ring a bell but that may be the ambient air reading.