% loss through drivetrain

[TheFirstEskimo]

Does anyone know the percentage losses through the drivetrain for an 07 GT?

I realise that Subaru say 184kw at 6000 rpm, but I'm guessing this is measured at the engine?

I would like to know the kw rating of a stock GT atw, so I can compare to my dyno runs. These are shown in HP only but I'm ok with that conversion!

Thanks

[mynameisdaniel]

It's not as simple as a percentage (linear) loss. Also depends on manual or auto.

From what I've seen, about 130-135kW ATW from a manual stock.

[QuarterMile]

That 184Kw is likely taken at the wheels.
184kw at the flywheel for a turbo car is depressing low.
just my opinion, what would i know.

[mynameisdaniel]

That 184Kw is likely taken at the wheels.
184kw at the flywheel for a turbo car is depressing low.
just my opinion, what would i know.

Do you drive a Liberty? Because I've got bad news if you do...

[QuarterMile]

That 184Kw is likely taken at the wheels.
184kw at the flywheel for a turbo car is depressing low.
just my opinion, what would i know.

Do you drive a Liberty? Because I've got bad news if you do...

I do, its a 2.2 Na though, so I don't really know much about Libs with power.
Is that really all they produce at the flywheel?

[Deep Heat]

I do, its a 2.2 Na though, so I don't really know much about Libs with power.
Is that really all they produce at the flywheel?

Most manufactures figures are flywheel.

[dr20t]

I do, its a 2.2 Na though, so I don't really know much about Libs with power.
Is that really all they produce at the flywheel?

Most manufactures figures are flywheel.

All of them are

To answer original question - drivetrain percentage loss for manual is roughly 20%

25% for an auto depending on its age (due to Convertor and clutch pack slip which will get worse as time goes on and thus put less power to the ground and increase the above losses)

It also depends on the load you're talking about. At low load, the losses are alot higher (especially for an auto Subaru due to the transmission computer not giving full torque Convertor lock up until higher load / higher gears)

Example - 2nd gear in a 5eat will only ever give you about 80% torque Convertor lock up unless you have an aftermarket transmission computer, 3rd will give you 100% depending on requested torque and load, as will fourth and fifth

Hope this helps
Mick

[kiahatsiu]

I have read, and also roughly confirmed with things like moroso calculator that it is about 50kw loss through the 6 speed.

[paggaz]

I have read, and also roughly confirmed with things like moroso calculator that it is about 50kw loss through the 6 speed.

I'd also agree. All the dyno runs of stock GTBs which I've seen have been around the 135kw atw mark

[jslayz]

Surely.......

The loss through the drive train is a fixed value.

The weight of all components plus the friction of all bearings and shafts rotating in fluid = drivetrain loss.

This can only be a % after you know the cars power level.

If your car has a different power output the % will be different......

J

[swingn]

I do, its a 2.2 Na though, so I don't really know much about Libs with power.
Is that really all they produce at the flywheel?

Most manufactures figures are flywheel.

All of them are

To answer original question - drivetrain percentage loss for manual is roughly 20%

25% for an auto depending on its age (due to Convertor and clutch pack slip which will get worse as time goes on and thus put less power to the ground and increase the above losses)

It also depends on the load you're talking about. At low load, the losses are alot higher (especially for an auto Subaru due to the transmission computer not giving full torque Convertor lock up until higher load / higher gears)

Example - 2nd gear in a 5eat will only ever give you about 80% torque Convertor lock up unless you have an aftermarket transmission computer, 3rd will give you 100% depending on requested torque and load, as will fourth and fifth

Hope this helps
Mick

Very well said mate

Surely.......

The loss through the drive train is a fixed value.

The weight of all components plus the friction of all bearings and shafts rotating in fluid = drivetrain loss.

This can only be a % after you know the cars power level.

If your car has a different power output the % will be different......

J

There is a running debate on this sort of thing. I've been told & have read that if there is a drive train loss of say 100kw on a stock standard car, then with mods, the loss after the car has been modified is the same. IE: Not a percentage... For example 353kw stock car = 300kw ATW's... Exhaust + Tune gives you 400kw at the flywheel, therefore new power at the wheels "should" be 347kw.

I don't 100% agree (Although there is a degree of logic to it) on this as there are so many variables that can effect this & would suggest this is why a drivetrain loss as a percentage is commonly accepted.

On another note, a rolling road dyno also suffers from inconsistencies from tyre rolling radius, tyre pressures, etc etc etc. HUB dynos, which will obviously give you a higher power reading as the it removes the tyre & wheel variables, is said to be a more accurate way of reading power - Short of actually having an engine dyno of course... Then we start another debate of how to convert this into ATW's power, but this can be done with a good degree of accuracy, just don't ask me what the formula is

Oh, & for all you 2.0T Gen 4 auto drivers... You have approx 115-120kw ATW's in a stock car... Huge loss considering it's 180kw at the fly / engine, which is a percentage loss of approx 35%... So show big respect when you see these cars pushing out 200kw ATW's plus!

[Robbks]

from lots of long discussions on this there's around a 30% on average loss that seems to hit a ceiling at about 50KW (for manual's, bit more on Auto's as discussed).

i.e Stock GT forester, 125-130KW flywheel will run 90KW ATW on a dyno (30%)
stock 160KW GC8 WRX is running about 110KW ATW
Stock STi, 206KW will push about 155-160ATW (25%)

but when you're getting up to 300KW+ cars, they're not dropping 100KW,
still only dropping around the 50KW mark

[dr20t]

from lots of long discussions on this there's around a 30% on average loss that seems to hit a ceiling at about 50KW (for manual's, bit more on Auto's as discussed).

i.e Stock GT forester, 125-130KW flywheel will run 90KW ATW on a dyno (30%)
stock 160KW GC8 WRX is running about 110KW ATW
Stock STi, 206KW will push about 155-160ATW (25%)

but when you're getting up to 300KW+ cars, they're not dropping 100KW,
still only dropping around the 50KW mark

Spot on

I should have put a qualifier on my original post

[TheFirstEskimo]

Thanks for the info guys, very informative. So given that I drive an auto, I have come to the following conclusion...

My second run on the dyno (hub type), produced a maximum of 226.2 hp. If I covert this to kw by multiplying by 0.745699872, then apply a derating factor of 25%, Im left with a figure of 126.51 kw atw.

Does this sound reasonable? Car is not stock and has had exhaust mods and engine mods done.

[jslayz]

Do you have a pre mods dyno figure on the same dyno?

J