[Rhody]

Parallel axis gears, such as transmissions, rob far less power than perpendicular axis axis gears, such as rear ends and steering boxes. The lack of a transmission is beneficial in terms of overall car weight and driveline packaging. Getting rid of the clutch and flywheel gets rid of rotating weight which is a big advantage in accelerating and slowing down the driveline, but doesn't have a big influence on steady state power. Driveshaft alignment will also have an effect on rear wheel power, and any difference in tire circumference will show up as a power loss. The general rule of thumb I learned is that any gear set that changes the direction of power (ie rear end, steering box) is going to cost you 15%. Then add on losses from there.

[rmr6nm]

Very good points, but for my purpose, not as relevant. I don’t discount the application of power to the ground and am very aware. But for this exercise I wanted some sort of % of loss when comparing supposedly like motors. The 10% number sounds a little more valid. Was hoping to be lucky enough that someone had both for the same motor.
Thanks to everyone!

[spankytoo]

Originally Posted by rmr6nm Very good points, but for my purpose, not as relevant. I don’t discount the application of power to the ground and am very aware. But for this exercise I wanted some sort of % of loss when comparing supposedly like motors. The 10% number sounds a little more valid. Was hoping to be lucky enough that someone had both for the same motor. Thanks to everyone!

Call Engler, great guy, does many dyno tunes and he will be straight with you.

[kendirt]

Originally Posted by spankytoo Call Engler, great guy, does many dyno tunes and he will be straight with you.

Please report back here if you do.

My feeling is that 10% is a touch high and that it will be more of a fixed number than a percentage anyway.

I know that like in street car drag race stuff for a given driveline combo the hp loss will be almost identical whether it's 600hp NA or 1000hp turbo'd.

[Rhody]

The friction generated between gears is a function of the force on the face of the gear tooth times the friction of the surface. Therefore, the higher force pushing on the gears, which goes hand and hand with more power, results in more frictional losses. To test this, drive your pickup around the block for 10 minutes at 25 mph, then measure the temp of the rear end. Let it cool (if it even got warm)and then get on the highway and stand on the gas for 10 minutes. Check the temp again. The higher temp indicates that more energy was lost when operating at higher horsepower.

[TQ29m]

You might be able to strain gage a shaft that you could use in both applications, run it with the dyno, then with the car, and compare the data.

[2rock21]

7% for a sprint car

[jdperform]

That depends on the calibration of the dynos being compared. I was wondering the exact same thing bout 10 years ago. Sooo we ran a decent 410 (GB engine) on an engine Dyno made as expected around 830 peak. Then with a quickness pulled it out. Put it in a car and chassis Dyno tested about 2 hours later. It made 787 so about 5%.
Having said all that I’ve never seen a Dyno sheet win any races.

[dstensland]

I was told by Tim Engler to multiply his chassis Dyno HP result by 1.07 (7%) to get engine Dyno HP result.