Ringpeas

Have seen a dyno printout of a WRX with 320bhp from the engine and 220bhp at the wheels.
Can this be right???
That is 100bhp loss through the transmission. That is horrendous, a lot of cars only produce 50bhp so how do they even move?
I am sure that I must have got the wrong end of the stick, so somebody please enlighten me.
If it is the 4wd, then is ir realy worth it?
A rwd scooby, now that would be fun!

Carl2

That works out at about a 32% transmission loss. I think that sounds too high, but I don't know what it should be. Fwd and Rwd cars are about 12-15% so I'd have though a 4wheel drive would be under 30%. but who knows?

scooby-si

mine was 80bhp loss hopefully now 60 ish

TonyBurns

iTrader: (3)

Ive seen a type RA V-ltd push out 327bhp at the fly and 270ish at the wheels (different transmission losses due to the different type of diffs used).

Tony

Flat 4x4

Mine is 220bhp and 165bhp at the wheels and that's with a Haldex 4x4 system (Skoda)that's less power sapping than a permanent Subaru set up. It certainly uses a lot less fuel for similar power to the Impreza.

chrisp

63bhp the TL on my RA.

chrisp

On the same dyno day as me two P1's, TLs were about 100bhp give or two the odd bhp.

hypoluxa

Rolling roads do not measure transmission loss, they measure coastdown drag. Very different.

22-23% losses as a ballpark figure. Excluding the centre diff specials

Ringpeas

Thanks guys.
Even more confused now!
What is coastdown drag?
Why is transmission loss a percentage, rather than a fixed value for each system?

Fuzz

Coastdown drag if your being picky was 89 BHP on my UK 00MY I have seen many around this figure and some at 100 BHP.

I would assume the figure would be less with a lighter flywheel ??

Andy

jusb

4 wd power is being sapped up by gearbox, prop, diff, 4 drive shafts and 8 cv joints but i reackon its no more than 60 bhp loss
too many exgarationists fantasisers on this forum

chrisp

Mine had the lowest % wheel drag on the day

hypoluxa

Say you have a car that develops 200bhp at peak power and say transmission losses are 25%. You will have 150bhp at the wheels. At 2000rpm and part throttle lets say engine power is 50bhp, PAW would be 37.5bhp. If transmission losses were fixed (at 50bhp) you wouldn't move

To measure transmission loss there has to be an input into the transmission for the transmission (i e everything between the flywheel and road) to lose Rolling roads measure transmission losses with the engine disconnected (car is in neutral). So whatever is being measured/recorded is not true transmission loss.

Ringpeas

Thanks guys.
I get it now.
It seems to be diminishing returns from power gains over 200bhp on that system. Guess thats why they give such poor fuel economy!
Mark

Fuzz unplugged

Jusb wrote:
explain this then

note two overlaid graphs done at different times of year with different mods and still the drag shows within 1 BHP of each other.



Andy