Transmission Losses

As I've mentioned in another thread, my completely standard J-Spec TT auto is apparantly making 305bhp at the fly, but only 220 at the wheels..... could someone tell me if this is normal? To me that seems like a huge loss.

The car seems to go like stink but I'm a bit concerned that I'm missing out on a few BHP because something's knackered.

Here's my power graph:

No-one?

Anyone else got any examples of standard transmission losses on an auto? Is 305 - 220 acceptable?

Did they actually take the engine out and dyno it then? And then put it back in and do a RWHP run too?

Cos otherwise it's just a percentage figure they type into the computer and it works out your flywheel figure isn't it?

Scoboblio,

305bhp less 28% drivetrain losses = 220bhp at the wheels

Basically the dyno operator has guessed that an auto TT suffers 28% drivetrain loss and applied that calculation.

Seems that you are worrying about "Where's my 305bhp gone?" but in fact your car never had 305 to start with.

A more likely figure is:

275@flywheel less 20% losses = 220@wheels

Thanks for the replies guys

I was under the impression that transmission losses were calculated by how much resistance the car offers against the rollers when it's winding down from a run..... but that's quite possibly horse manure.

Jake, my question isn't "where's my 305bhp gone" but "is my transmission knackered?"

Of course if the dyno operator simply guesses that an auto suffers from 28% drivetrain loss then like you say my fly BHP is 275 which is much less than it should be. hence I'm trying to find out if anyone else has any fly to wheel power figures for a standard auto so I can compare.

I'd like to know transmission losses on a TT6 as well.

Unfortunately it means taking the engine out of a good condition one and dynoing it!!

Fair enough, so in order to be accurate you'd need to remove the engine.

But 220BHP at the wheels still seems too low to me. Now either the transmission losses are made up and my engine's not producing the power it should do, or the transmission losses are accurate and I'm losing a hell of a lot of power between fly and wheels.

Or the dyno's not accurate and I'm worrying about nothing

Don't know much about the auto if it was manual you could probably check for clutch slippage etc.

Could be a dodgy dyno reading.

Could be that you actually do have the fabled 280bhp that the japs claim!!

I have to say it's a funny shaped graph as well - doesn't look right to me, but then I don't know much!!

Originally posted by tbourner

Could be that you actually do have the fabled 280bhp that the japs claim!!

lol, would probably be a first!

When my manual was dyno'd they estimated 19% transmission losses, 360rwhp = 429.5bhp.

Does my power graph look wierd to anyone?

I've just notice that the power dips before #2 comes online (as it should i believe), but so do the revs

25% for autos, 18 for manuals. (For wheel horsepower loss)

Originally posted by Bobbeh

25% for autos, 18 for manuals. (For wheel horsepower loss)

Thanks dude

It looks like it clips backwards though.

So at just over 4500 revs you are actually getting 3 different power figures!!!

Would like to see the AFR graph.

Don't have the AFR graph unfortunately

Think I'm gonna take it to another local dyno, will be interesting to see what happens.

Scobob was this done at engine advantages??

Originally posted by letmeshowyou

Scobob was this done at engine advantages??

Yes mate it was.