That's a relief

After my previous experience of putting my newly purchased GT4 on a rolling road only to find it had a split in the block, today my new Sup went on the rolling road and hit 318bhp with 214 at the wheels. I was pretty pleased it's running like this seeing as it's totally stock and has done 93k (also has a tow bar fitted ). I was told the figures may be a little out due to having it restricted still, is this right ?

 

Anyway, now it's been confirmed as sound I can sort out some serious modding.

 

Mine's a J spec TT Auto by the way

Originally posted by Rob Andrews

After my previous experience of putting my newly purchased GT4 on a rolling road only to find it had a split in the block, today my new Sup went on the rolling road and hit 318bhp with 214 at the wheels. I was pretty pleased it's running like this seeing as it's totally stock and has done 93k (also has a tow bar fitted.

 

I must admit that I think the transmission losses are excessive, thats virtually 33%!

 

If it was 214 at the wheels I'd really have expected no more than 245-255 estimated crank bhp, which is a bit down on standard, but if its restricted in some way this could account for it.

 

As for the towbar, Dudes car has never run so well since he fitted his, they're without doubt an extremely underestimated source of bolt on power

yeah, losses were pretty big all day long. That was the main topic of conversation, I thought you should be looking at 25%ish losses, some cars were showing nearly 50% loss.

 

The nice thing was I actually gate crashed the Mitsu Colt club power run day. After they had all run, my mate put his Teg R on and got 196 and someone said 'we still haven't got a car in the 200's yet'. Mine went on next and afterwards I smuggly pointed out there still wasn't a car in the 200's !!

Originally posted by Rob Andrews

some cars were showing nearly 50% loss.

I don't understand what you mean Rob. How was the loss figure being calculated? Don't they take the figure at the wheels and add on a certain percentage?

their computer shows engine output and wheels output, it's not done by any calculation afterwards, just whatever the computer reads during the power run. is that what you were wondering ?

Sounds a bit odd to me. What kind of car was it that the computer was allowing a near 50% drivetrain loss?

I got 329bhp at the flywheel and 246bhp at the wheels on my stock J spec

Originally posted by GeordieSteve

I got 329bhp at the flywheel and 246bhp at the wheels on my stock J spec

That sounds like a more believable figure, Steve. It seems like the flywheel figures being quoted be the place Rob went to are being over-estimated by quite a large margin.

My Jspec auto TT got 318(atf) and 266(atw) when I had that dyno'd................

I still don't underestand why flywheel power measurements are given when only rwhp is measured.

 

There's obviously a bit of science involved in calculating a figure, but surely it's always going to be a very rough estimate?

 

That being said, I - like most people - like quoting my estimated flywheel hp as it's bigger

214 RWHP = 285bhp according to my calcs of 25% loss.

Originally posted by Bobbeh

214 RWHP = 285bhp according to my calcs of 25% loss.

 

So with my measured rwhp of 300.8, my crank hp would be about 400bhp.

 

Seems unlikely with my minor mods - or have I got the wrong end of the stick

looking at my print out, the loss figure jumped up a lot at 80mph, which happens to be when 4000 rpms are hit. am I right in saying that if this is to do with the second turbo cutting in then there isn't anything wrong with the turbo as the engine output is still good but the power is being lost somewhere between the engine and wheels ?

 

If that's the case then I'll be checking hoses asap. Any advice ? Didn't someone else have a loss of power on 2nd turbo recently ? I only get a small kick when getting to 4000 rpms, shouldn't I be getting a bigger kick on a stock setup ?

Originally posted by Grazer

So with my measured rwhp of 300.8, my crank hp would be about 400bhp.

 

Seems unlikely with my minor mods - or have I got the wrong end of the stick

 

No, autos were rated for 25% loss, manuals 18% loss, so your power would be circa 365.8bhp. Your quoted figure is probably as accurate as this, considering you have an uprated clutch.

Originally posted by Bobbeh

No, autos were rated for 25% loss, manuals 18% loss

 

That makes more sense

Originally posted by Bobbeh

No, autos were rated for 25% loss, manuals 18% loss, so your power would be circa 365.8bhp. Your quoted figure is probably as accurate as this, considering you have an uprated clutch.

 

EDITED: I'm Gei!

I was under te impression that drivetrain losses were calculated by the over-run once throttling off on the rolling road. But i'm probably way out

Originally posted by SirCharlesworth

I was under te impression that drivetrain losses were calculated by the over-run once throttling off on the rolling road.

Not that I'm aware of.

AFAIK drivetrain losses are always a pure guess unless you're prepared to take the engine out and have it bench dyno'd to get the real @flywheel figure.

Strangely, some folks are reluctant to go that route.