Doyle623

What percent is the drive train loss on our cars? (12-15%?) My question is.. is that figure the percent of the power lost from the stock HP, or does that percent hold true reguardless of how much power you are putting out? Does it only take X amount of power to move the drive train parts or does the amount lost increase as the HP increases? Would one of our cars putting out 500 bhp lose 75 HP through the drive train while a 300 bhp lose 45 HP at a 15% loss?? Thanks, hope I wasnt too confusing.

sharky47

I don't know the % - but I would imagine the loss to remain the same regardless of what the engine is doing.

schnellfahrer

I was under the impression that driveline loss (in percent) is lower as power goes up. I spoke to someone who told me that he saw 12% loss on a stock 944 turbo, and 9% loss on a 400hp 944 turbo.

Laust Pedersen

The main loss in a driveline is from the pre-meshed gears pumping oil like oil pumps without a purpose. Then there are the smaller losses from bearings and seals. None of those are significantly affected by the torque transmitted, but particularly the hydraulic loss is rpm dependent. Unfortunately I have never seen a driveline loss curve, but there are transmission dynamometers that can create them:
http://www.superflow.com/dynamometers/index_138.cfm

Laust

95ONE

This topic came up on an NSX forum a little more than a few years back.
The link is at the bottom. Warning it's three pages long or longer. I can't remember. I read all pages about 10 times to fully grasp his techno babble, He Designs transmissions for Mustang Engines and it's his job to make them use less horsepower and still maintain strength. He lives here in Houston. Interesting gentleman! But in General it confirms what the next few post say by proving that The percentage does drop after a while, but it stays about the same for most horsepower levels. Due to Frictional Forces as pressure rises, etc. etc. etc.

Well. I can see that the sticky that was in the Tech forum has been removed . I think it's over 5 years old. but here is a cut and paste of what he replied to on a similar topic some years later.

"This topic came up on The Tech List a couple of years ago. 1% power loss per gear mesh is a good number to use. I calculated the theoretical power loss in the NSX to be 12% and this takes into account the traverse engine configuration. For comparison I also calculated the power loss in a front engine American car with a driveshaft and rearwheel drive. I don't recall the exact number, but it was close to the NSX's 12%. Therefore, the engine configuration - traverse or longitudinal - has little to do with power loss. It is a function of how many gear sets and CV joints there are between the flywheel and tires.
"

Trucho-951

I would like to add my $.02. I’ve thought about this in the past and have come to my own conclusion that drive train loss should remain fairly constant. Here is my reasoning.
If the stock 951 engine is rated at 217 bhp and 184 whp, then that gives us approximately a 34 hp drive train parasitical loss (which incidentally is approximately 15% of 217 hp).
This is despite of engine mods made to improve the power. However, the DT loss would increase and would need to be accounted for if for example we now spin the engine to higher RPM (which spins transmission gears faster in a viscous oil), and/or we have added bigger and heavier wheels and tires in order to take advantage of the greater hp (greater rotational inertia).
I do not like to think of if in terms of percentage loss, but rater as a proportional loss related primarily to RPM. For a quick and dirty approximation of DT hp loss (assuming stock tires and wheels), I estimate it by using the following formula: DT = 34 hp *RPM/5800. So for example, if I add a new bigger turbo that allows my engine to make max. hp at 6,500 RPM instead of the factory rated 5,800 RPM, my new DT loss = 34 hp *6500/5800 = 38 DThp loss.