Im starting this little discussion on why our Subaru's seem to loose so much in transmission, and the reason that even when we loose so much this way, making our cars slower!!! than they actually are (even though we can kick 911 *** etc) do we get on average of 280bhp a loss of 80bhp!
Im no mechanical engineer etc but ive thought this through and see what your opinions are on this (all opinions are welcome back!)

We all see the rolling road figures from the american WRX's, most of these with only minor modifcations push over 200bhp@wheels (not normally pushing more than 250bhp@flywheel) so why do our uk cars (and jap imports) loose so much in transmission losses?

One of my thoughts is that we dont actually loose that much in transmission losses, and theoretically our cars act like rwd, front engined cars as this is the longest distance that the power has to travel to turn the rear wheels, also theoretically the greatest loss of power!

You can run a 4wd/fwd or rwd car on a 4wd rolling road, on doing so you run a fwd and rwd car on just one of the rollers (even though the car is on both rollers) and the power figure is obtained that way.
My theory is that when a fwd or rwd car is running on a 4wd rolling road, the software calculates by using just the one roller so for 4wd it should calculate for both rollers, should it not?
But say for instance, that when calculating a 4wd car (which on average has TWICE the loss to transmission than a fwd or rwd car) it actually calculates twice! and therefore shows greater losses towards fwd cars.
Your average rwd car has (theoretically) greater losses of transmission due to the power being sent further than a fwd car, and as our cars should act more like rwd than fwd our losses should be that of a rwd car.
If instead of the rolling road calculating once the power@wheels on a 4wd car it actually does it twice, once for the front wheels and once for the rear wheels.
Knowing that the loss should be the same for both front and rear on a 4wd car due to the single shaft between front-rear (also taking into consideration the differentials which shouldnt loose virtually any bhp) is not the rolling road then adding both sets of losses up and coming up with a larger loss than normal?
Please dont talk about the wonderful amounts of grip our cars have over hot hatches etc as a properly launched hot hatch will have virtually zero wheel spin (losses of .1 to .2 of a tenth of a second) and yet they are still 5 secs behind a std uk car which on average is only pushing 150bhp@wheels! (take into account that most hot hatches loose 30bhp and look at cars like the seat cupra 1.8t 180bhp and my last 306GTI-6 had 147bhp@wheels and was nowhere near as quick as a std scoob).

If we look at where our cars loose the power (engine-drivetrain-wheels) we find that it should take the same power to move the rear wheels as it should the front, and if it takes 40bhp loss to move the rear ones, that same 40bhp loss should also move the front ones at the same time resulting in 40bhp losses moving BOTH and not one set of wheels.

So if you can understand what im trying to get at, ie the losses on a rolling road are added twice due to the fact that the rolling road may mistake the vehicle as pushing say a 40bhp loss on both sets of wheels (where as it will be a 40bhp for all the wheels) and then adds these together making our cars look slower than they actually are!

End of waffle, all replies welcome

 

Erm Yes...and no !

I believe the losses are calculated by the rolling road during the rundown after a power run. This is done by the rollers having a controlled rundown period during which the rollers actually drive the transmission. It is the power taken to drive the rollers that is used as the 'drag' figure.

So the rear wheel rollers drive the rear wheels, hubs, shafts, R diff and contribute to 50% of the centre diff/gearbox load.
The front rollers drive the front wheels, hubs, shafts, F diff and the other 50% of the centre diff/gearbox. (assuming a 50/50 ctr diff)

So when you have a FWD or RWD car on the rollers, the measured losses do not include the stationary, non driven ends losses ie the rolling resistance of the laden tyres/hub on the rollers.

Just exactly how much these losses amount to ????? I don't know.

A 2wd and 4wd cossie will show the same PAF as each other but differ by approx 25 bhp at the wheels. Regarding performance they are very similar, the difference being mainly due to the weight disadvantage of the 4wd car.

 

Whatever, on the road for their power to weight ratio irrespective of losses, they hold up well compared to 2WD cars with similar gearing and power to weight ratios, so it can't be all that bad.

 

Thats what i think John 4wd losses are not what they are made out to be thus the reason ive started this debate

Tony

 

The 4wd will always show greater losses due to the increased amount of rotating parts in the driveline ( and friction on the rollers ). ie, wheels, hubs, shafts, diffs etc. a typical 2wd car i think is ususally estimated to lose around 15-20% while a 4wd can be more in the region of 30% Different 4wd layouts would also affect this. Ford use a fixed drive split, with transfer box and seperate front diff, so possibly might show more losses? evos/celicas ( a friends celica at PE went from 329@flywheel to 235@wheeels ) etc are basically a front wheel drive cars modified to 4wd so probably poor too. They all almost make the subaru look reasonably efficient in design.
While your 306 may have shown 146bhp at the wheels, It is probably a revvy peaky engine. What it wouldnt have is the torque spread that a turbo gives. Horsepower numbers arent the be all end all. After all, a 1300 motorbike engine might make 150bhp, try putting that same engine in your 306!!!! i dont think it would go very fast.
I am sure the people who make the rolling roads and the associated software know a little more about it than most of us. If nothing else the rollers will give repeatable results for testing purposes, and to show whether modifications actually work. That is why they are such good tool for tuning. Some rollers may read high, some low ( although they should all be very close if calibrated ). It doesnt mean your car has less power on one set of rollers. At the end of the day, some people just want a printout with big numbers on it for the pub. I think that on the road is the true test of power/torque, or at the dragstrip. A good 1/4mile is a good indication of power, higher terminal indicates more power more so than a good time.. ( for similar cars of course ) A car with a slow time might still pull 120mph at the end. 280bhp aint gonna do that even with a good start. And another thing about drag racing...Its more fun... as are track days, although a little more risky. So get out there and drive.

 

oops..

[Edited by ustolemyname??stevieturbo - 5/8/2002 8:45:18 PM]