marc_gtir

Hi,

I own a Pulsar Gtir (sorry!) and i was just interested what sort of losses you guys get through your drivetrain? Its just some guy recently rolling roaded his Gtir at 320bhp at the flywheel but he was only getting 220bhp at the wheels. I mean, 100bhp loss, that seems a fookin lot.


Cheers

Marc

HarryBoy

Have a look at the Dyno site, dyno.scoobynet.co.uk.

It's not untypical to get losses in the 40% region with the Impreza

Harry

john banks

It seems that rolling roads often vastly overestimate the transmission losses and therefore overestimate the flywheel power. 220BHP at the wheels on an all wheel drive car is very respectable indeed. That is what it puts on the tarmac after all. But 40% would be a massive amount of heat to liberate through the drivetrain !

R19KET

John,

Interesting comments. The only problem, is that if you're correct, then based on stock STi's getting circa 190bhp ATW's, are you saying that the OEM quoted power figure of 280ps/276bhp is greatly exagerated ? Similar for UK spec' cars.

I've found that ATW's figures are no more reliable, than the F/W figures, they vary just as much (pro rata) from RR to RR.

It's interesting that the US estimate drive train losses much lower than we do, hence they get far higher ATW's figures, apart from a few guys who get circa 300bhp ATW's, they they prefer our drive train losses They seem to have quite a few '02WRX's running circa 400bhp F/W........... Not bad from 18~20psi. Wish I could have got it.

Mark.

R19KET

John,

The US consistantly get circa 220bhp ATW's, from a TD04, running 12~15psi. They also get circa 175~180bhp ATW's from a stock car ! In the UK, these are pretty much STi figures.

These are considerably higher figures than we see, and I don't believe it's down to "tuning ability".

So, the only thing left is RR software, and as we all know, this can vary dramatically. This idea was actually suggested by a very respected US tuner, who also couldn't understand the diparities.

Now it may well be, that the US figures are correct, and ours are inaccurate, this would also seem to fit with your ideas, that the DT losses are less than we think.

A lot of guys in the US are under the impression, that 400bhp F/W is pretty easy to get, running 20psi, and stock internals. Some of them are already getting well over 300bhp ATW's. In the UK, the highest I'm aware of, is Craig H's car, that got 288bhp ATW's, and that was running 1.8bar/26psi, no one else has come close, to my knowledge. All the PE'd 350bhp F/W cars run 230~240bhp ATW's.

It will be interesting to see how my engine dyno figures, compare to the RR. But then, who knows how accurate the engine dyno was ????

Mark.

GavinP

Following on from Mark's post, surely figures between a UK car, a JDM WRX and a STi should vary ?

If the gearboxes and diffs are different, then there should be a variation between the losses ?

Thanks

Gavin

R19KET

Gavin,

I agree, one would expect to see some variation, purely down to gearing, but the disparities are too great. I'd estimate that the US are getting about 40~50bhp ATW's, over the UK. That's MASSIVE.

Mark.

WREXY

I would say it's the RR software too, cos in OZ most tune shops have the Dyno Dynamics brand rolling roads. The MY00 standard cars in OZ get 119hp at the wheels on these dynos. No flywheel powew figures are given on these RRs. In the UK the MY00 standard cars get around 140/146 hp at the wheels and the cars have the same specs.

Cheers,

wrexy.

R19KET

Wrexy,

I think you'll find that the AUS RR figures are quoted in NM, and IIRC, these would be higher than the UK figures too.

I'm begining to think we're getting done well, on the ATW's figures, anyway........

Mark.

john banks

Some standard cars produce as little as 119 PAW on the MAHE (sic??) rolling roads like Star or Powerstation.

Cosie Convert

Our local rolling road at Star Performance (MAHA), as far as I could see, has the rollers geared together. This means that there are 2 contact/working patches per tyre instead of 1 on the road.
My understanding is that this is responsible for the additional losses.

I wonder if the USA R/Roads are similar ? Or is it possible that they only drive the leading roller, with the trailing roller freewheeling and only used for positioning ? This would reduce the losses.

Also, I have my doubts about the way the losses are calculated.
The rollers record the power required on over-run to spin the transmission, this = xx bhp however, these losses are measured with the clutch in and no power transmission from the engine.
There will be 2 components to the trans losses, one a base line rotational loss and 2 a percentage of power transmitted loss.
How does the R/Road calculate this value ? There is no power being transferred during rundown

MattRus

My two pence worth!
Rolling roads measurement of torque should only really be used as measurement of change, run to run, modification to modification, not as a finite value. There are to many variables to take into account, frictional losses, atmospheric changes, calibration etc.etc..
All pro race teams & engine developers use engine dynos. that measure flywheel torque / power. These are naturally more consistent with their results due to fewer variables effecting the results. But even these are only really interested in change not in how large the figures are.
There are also several different types of dyno (or engine brake) that measure the torque / power in different ways.
Best measurement is lower lap times or quicker on the road!

Perhaps someone out there works for a Dyno manufacturer who can help with some fact's?

Cosie Convert

I use an AP22 performance meter and think it is a brilliant tuning tool ! As you say, it's the change that matters, not the number
I have tried more things on my car that lost power than gained power (they didn't stay on long )

WREXY

Mark,

The Aussie dynos display in Kw for power and Nm for torque. I never see the torque figures posted, so I can't compare those to the UK cars.

The MY00s get 89kw in OZ, which when converted to hp (x 1.34) you get 119hp.

I suppose it comes down to the brand and the software.

So you aren't getting done I'd say.

R19KET

Wrexy,

OOPs, you're right, I meant to say KW.....

What do you mean I'm "not getting done", whatever I get, I ALWAYS think I should be getting MORE

Mark.

Bitten Hero

Interestingly, I talked to Mike Wood at Prodrive about this a while back. He was saying that rolling roads don't give a true indication of the losses - indeed he said that standard cars were giving out up to 180bhp at the wheels, but this was at the official Mira windtunnel, which is where they go to prove out their mods. He was most dismissive of rolling road values (and I wonder why?)

Though interestingly I've had 254bhp and 255bhp from two completely different rolling roads, which is pretty consistent as far as I'm concerned...

Richard

RobJenks

I agree with WREXY , standard WRX's never exceed 100 kw at the wheels - most circa 98 Kw.
That is a tranny loss of 60 kw's - If we believe the engine spec from Subaru.
I have personally witnessed a 170 kw @ wheels.(220bhp)
MY2000 , Unichip/FMIC/Garrett from Nissan 2000/Jap exhaust.

GavinP

Mark: Yes, I appreciate that wouldn't explain the difference between UK and US figures - I meant on UK RR figures between individual cars.

Incidentally, I have read a few articles about owners in the U.S. using figures with just two wheels driven - this may explain the large difference...?

Thanks

Gavin

john banks

A certain Evo got 371 F/W and then about 320 F/W IIRC just from fairly small changes in loading and different run length with something like a halving of the drivetrain losses. Inaccurate science? Pseudoscience more like... This is on a supposed state of the art rolling road. Who is to say what settings are correct? Perhaps if losses really are >40% (where does all that heat go?) we should be working on reducing those rather than making our engines more powerful at the flywheel - but I expect you have a few plans

I am puzzled though - how do lower US drivetrain losses give them a higher power at wheels since the torque at wheels is actually measured and the power at wheels is calculated from RPM, the drivetrain losses and hence the flywheel power (with temperature correction) then being calculated from the down run?

[Edited by john banks - 4/9/2002 9:23:27 AM]