Transmission Power Loss

Donovan · Post by **Donovan** » Thu Jun 14, 2012 8:23 am

Does anyone know what the average loss of power is from engine to wheels in a RWD or 4WD car? If I have an at the wheels power rating, is there anyway I can work out what the power is at the flywheel?

punkoutnz · Post by **punkoutnz** » Thu Jun 14, 2012 8:26 am

It's different between a lot of cars aye. Did they not let the wheels drag after your power run? This gives them a pretty accurate figure for drivetrain losses and then they can calculate your engine power based on that.

Donovan · Post by **Donovan** » Thu Jun 14, 2012 8:46 am

Don't know what they did, this was for the STi, just dropped it off to them in the morning, and picked it up later in the evening, paid the money, got the Dyno sheet and walked out the door, didn't think about asking them about the power at the wheel vs the flywheel.

MX5 is hopefully getting done in a couple of weeks time (cross fingers) so was just trying to work out what the difference between the two will be. The MX5 is getting done by a different place than the Subbie.

Both are Dyno tunes, rather than just a Dyno run.

punkoutnz · Post by **punkoutnz** » Thu Jun 14, 2012 9:41 am

Ah well they'll probably be able to tell you if you asked them, if they didn't do a run on your actual car they'd have a fair idea the power loss. I thought you were talking about the MX5 though, being a one off it'd be a lot more difficult to estimate.

Donovan · Post by **Donovan** » Thu Jun 14, 2012 9:47 am

The second one being done will be the MX5, but then again, I guess that isn't really going to be of any help, since it is all Holden running gear.

Keith Jones · Post by **Keith Jones** » Thu Jun 14, 2012 12:15 pm

Transmission losses for 2WD, RWD cars are generally in the 10%-15% range. Higher in the intermediate gears than in the 1:1 gear.

You need to be careful about applying factors to chassis dyno figures though. Some dynos build a factor into their readouts to give a calculated flwheel power, not power at the wheels. This factor can either a fixed %, or one based on a coastdown test on the vehicle being tested.

When you take the MX5 ask them. If they don't know, find out the make and model of the dyno and I might be able to find out for you.

Kieran · Post by **Kieran** » Thu Jun 14, 2012 1:12 pm

Yeah I thought the rule of thumb was 15% trans loss

Donovan · Post by **Donovan** » Thu Jun 14, 2012 1:38 pm

So for the Subbie, guess it is about 30% loss with the 4WD, power rating was 195kw at the wheels, about 250kw at the flywheel then.

If I am aiming for 300kw in the MX5, then should be looking at about 250-260kw at the wheels.

Torque Perfomance did the Subbie, Protune are doing the MX5. I'll find out the details from Protune when I drop off the MX5 their as to what they are using, and also see if they can work out the flywheel rating.

Protune know about my car, as they stipped all the AFM, ABS, Alarm, Airbag codes out of the ECU, and are biting at the chomp to get their hands on it. Want it for a couple of days, dunno how much of that will be tunning, and how much will be "road testing".

Growler · Post by **Growler** » Thu Jun 14, 2012 1:57 pm

The last time my car was on a dyno I was losing 15hp. This was a manual however...

Donovan · Post by **Donovan** » Thu Jun 14, 2012 2:00 pm

Is there another type of Transmission's other than a manual. I have heard about these automatic fandangled things, but they will never catch on, no one in their right mind would want to let a "computer" do their thinking and driving for them, would they

dynofiend · Post by **dynofiend** » Thu Jun 14, 2012 7:26 pm

Transmission losses can vary, and on a rolling road are usually more down to the friction between the tyres and the rollers, which is predominantly affected by the 'road' speed. You can apply any 'guestimate' you like, but the only way to get a halfway accurate flywheel figure, is with an engine dyno.

Growler · Post by **Growler** » Fri Jun 15, 2012 2:02 pm

dynofiend wrote:Transmission losses can vary, and on a rolling road are usually more down to the friction between the tyres and the rollers, which is predominantly affected by the 'road' speed. You can apply any 'guestimate' you like, but the only way to get a halfway accurate flywheel figure, is with an engine dyno.

This was with the back wheel hubs bolted to the dyno...

SLYDIT · Post by **SLYDIT** » Fri Jun 15, 2012 7:07 pm

Donovan wrote:Is there another type of Transmission's other than a manual. I have heard about these automatic fandangled things, but they will never catch on, no one in their right mind would want to let a "computer" do their thinking and driving for them, would they

they are called automatics because when i see one.... i automatically say NO!

Transmission Power Loss

Transmission Power Loss

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