Atf Vs Atw

[NISSAN GTR]

Quick one ! Had some new mods installed the other day on my GTR, the dyno= 210 KWs at the wheels , does anybody know what 210kw would be at the flywheel , just for interest !

[R31Nismoid]

Around 270-280

[SKYPER]

Roughly. I think Eric (person who worked on Gibson R32 GTR racecars and now builds Targa, road spec GTR's, etc) worked it out to be 35% loss when engine dyno was compared to roller dyno (was mentioned in a magazine, so don't know how accurate the info is) for R32GTR, R33GTR. Not sure what torque split was used, as I've noticed torque split affects the final kw output at wheels. More rearward bias = higher kw at wheels.

210kw x 1.35 = 283.5kw x 1.341 = 380hp at engine.

Edited February 26, 2010 by SKYPER

[NISSAN GTR]

Roughly. I think Eric (person who worked on Gibson R32 GTR racecars and now builds Targa, road spec GTR's, etc) worked it out to be 35% loss when engine dyno was compared to roller dyno (was mentioned in a magazine, so don't know how accurate the info is) for R32GTR, R33GTR. Not sure what torque split was used, as I've noticed torque split affects the final kw output at wheels. More rearward bias = higher kw at wheels.

210kw x 1.35 = 283.5kw x 1.341 = 380hp at engine.

35 % loss is a fair chunk of power thats suprising , i think every car should be rated at the wheels , great info cheers

[TiTAN]

there is no way to quote an exact figure short of pulling the engine out of the car and hooking it directly up to an engine dyno.

[PM-R33]

Before this thread spirals into the same argument as all the other threads, have a read of this:

http://www.skylinesaustralia.com/forums/Bh...drivetrain+loss

[R31Nismoid]

^ yep - read that...

I can't see it being 35% either way, that's absurd.

[jjskyline79]

35% loss hummmmmmm

Looky here

Thats 299bhp ATF

convert that to kw its 220kw just give or take

as a rule of thumb ive always calculated transmission lose at 15% as its not a continual torque engine

At the wheels mine would be around 255bhp or 188kw

Ok same car same rollers same guy stock manifold pressure no mods

255bhp 188kw ATF this time not wheels remember

Thats 217bhp ATW roughly 160kw ATW

Edited February 27, 2010 by jjskyline79

[tridentt150v]

The only way to do it is to dyno a large cross section of vehicles both at the wheels and on the engine brake. Then generate a generic table with error bounds attached.

If you take into acount, gearboxes, diff set ups, tyres, heat at the tyres, tyre pressure, power range, revs to achieve it, your doing better than me.

A car that revs to 12000rpm will create more friction, a 1000hp car will create more friction, your tyres with 50psi in them generally gives more power [one for the dyno queens to remember], different brands/types of tyres will dyno optimally at different times and heat ranges, a lock diff will absorb more energy early but may actually be better at higher revs because you are using both rear tyres equally and so it all goes around and around.

The only true way is to do both dyno runs with the same motor, even then you may not have the best tyre on for the job.

So any any equation or ROT applied is an approximation - end of story. But a ROT is OK to use as long as you accept the bounds it creates with a high and low pass.