Drivetrain Loss

I posted this on the exhaust thread and kind of off-topic. Here it is again. Does anyone know the percentage of drivetrain loss in the 996? I ask this because the exhaust thread showed 222 rwhp on a 3.4 Litre. That equates to 26%, which is way higher than I suspected. By comparison, 951s and 968s have loss at about 16% (I believe). Thanks in advance for thoughts or feedback. JKC

Not scientific and probably biased, but here is what TPC superchargers state on their product. C2 3.4 l. engine 434 flywheel 378 rear wheel 56 diff 12.9% % loss Big diff from the 26% stated but we do not know the conditions on that and you had to assume stock flywheel hp. Maybe they had a dog or the conditions were not optimal. Rb

The only way you'll know is to chassis dyno, yank the motor and then engine dyno or vice versa. For example John Milledge (Engine God) has done this with motors(many most likely) he's built and I seem to recall the loss was more like 10%-11% for 951's. I would assume (yet again making an "***" out of "u" and "me") it would be less for a 911. You might check out this link to info on dyno drivetrain losses

It's all in what theory you subscribe too. Some people believe that the percetage of loss is constant as you increase engine power. Others believe that as you increase engine power, the percentage of drivetrain loss decreases. For example: If you have a 300 hp engine and it losses 50 hp (or 16%) before it gets to the wheels, does that mean that if you make the engine hp 900 that it now lose 150 hp (16%) through the drivetrain? Or, does the amount lost through the drivetrain decrease percetage wise. Conversely, if you lower the engine hp to 100, does that mean you lose only 16 hp before it gets to the wheels? Only one theory is correct.

Upon reflection, I would agree that it varies with engine and transmission to engine and transmission. Nevberthess, I cannot see a 24% drivetrain loss in a modern automobile... Particularly a high performance automobile like the 996. Thanks for the input and if anyone has real numbers from a dyno to share, I'd like to see them. JKC

Loss is also effected by temperature of gear lube and what gear you are running in. It's funny how you used the words "real" and "dyno" in the same sentence as dyno numbers are NOT real, but a calculation which has as many variables as Carter has pills.

OK... Makes sense... Can anyone give me an average of drivetrain loss or rwhp or at least a range? Seems to me we ought to be able to do that at least... Thanks in advance. JKC

Figure 15% for a manual and up 20% for an automatic.

all wheel drive cars lose 20-25% through the drivetrain.

You might want to read the content of the link I posted earlier in the thread. You're saying that a 996TT is dissapating 105 hp worth of heat through the driveline and transmission? Right. Maybe people who dyno their all wheel drive cars are prone to "at the crank" hp exaggeration. Do you have an example of an engine dyno and a subsequent chassis dyno to illustrate those numbers? If you don't than it's all smoke and mirrors.

If the factory 300 hp is correct for my 2001 C4, then I experienced about 16% loss (manual tranny, all wheel drive).

My last car was an '04 Audi A4 1.8T. For that car, with the quattro, 25% drivetrain loss was the rule of thumb. Of course, 996TT may be an apples to oranges comparison. That said, I would not be surprised if the drivetrain loss was just as high with the Porsches. One thing is for sure, it sure feels like there are just as many keyboard warriors on this forum as the one I left...

This statement is only correct for AWD vehicles that have a permanent mechanical all-wheel-drive system. In the Porsche world this only applies to the 964 series. The 996 uses a viscous coupling which only causes measurable drivetrain losses when it activates. These cars have to be dynoed in AWD systems and as long as the front and rear wheel speeds are the same the difference in drivetrain loss between a 996 C4 and a 996 Carrera will be within 1%. The 1% covers the front drive shaft turning in the input section of the viscous coupling. The average drivetrain losses I have seen calculated on reliable dyno machines over the years for the 996 series have been 16 and 15% for higher mileage ones and down to 12 and 13% for the lower mileage ones respectively. Ciao, Adrian.

Sorry. Didn't mean to come off cross. Still losing 40-50 hp through the drivetrain on the very fine A4 would mean dissapating something like 37,000 watts. That's a lot of heat dude. I don't buy it. It may be the "rule of thumb" based on comparing the stated factory hp to chassis dyno results, but those comparisons are pretty much useless because there are way to many uncontrolled variables for it to be science. Think about grabbing the rear drive shaft with big pair of pliers hard enough to scrub off 50 hp. Do you think that might generate a little heat? Like maybe enough heat to melt CV boots or boil transmission fluid?