Transmission loss

[DMS]

I've done a search but can't find the answer I'm looking for...

Can anyone tell me what the EXACT percentage of transmission loss on a 172 is?
My car will be RR'd again soon and I want to calculate the flywheel power from the ATW figure without relying on the "rough estimate" figure that's fed into the dyno.

 

[Gaz.]

You'll never get an exact percentage from a book/written down as your gearbox may be more or less worn than another 172 gearbox.

You'd have to put your engine on an engine dyno, then run it on an accurate rolling road and calculate the difference.

 

[DMS]

OK. So what should it have been on a brand new 172?
I appreciate that my car isn't brand new and that the gearbox is going to be a bit worn. I just want to be able to compare what the RR says with what it "should" be. More so I can tell if the RR is being optimistic than anything else.
At the end of the day, the power at the wheels is what matters, it's just something I want to do.

 

[Gaz.]

Google says

Take into account power to the wheels figures though, and you're looking around a 22% transmission loss versus a 13% for the Clio roughly.

http://www.carsurvey.org/reviews/citroen/c4/r89672/comments/

Don't know how accurate that is. I've always used 15% for FWD cars.

 

[DMS]

That's the thing I was trying to address you see. Most people just use a rough figure for all FWD / RWD / 4WD cars but that's always going to be less accurate than actually knowing the correct loss percentage.

 

[sideways danny]

it's not a percentage

 

[maupineda]

it's not a percentage

What is it then, and how much.

Wonder why all clios are 140 - 150 ATW, and still report 170 at the fly, if this is true then it is an 18% loss.

However, if there is a number to better go by, that would be ATW figures and not worry about an estimated engine number

 

[DMS]

Surely whatever amount it is can be expressed as a percentage though? As long as there's an ATF figure to go by?

 

[stan*]

Its speed relative, so higher losses at higher rpm, so you cant specifically apply a fixed percentage for a true figure.

However this is what alot of dyno manufacturers do...i guess because when you consider other quantifiable variations such as tyre deformation, strapping force etc etc, then relatively speking its accurate to apply a fixed percentage.

 

[TooneySonic]

as above - but you can generally apply 17%