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Originally Posted by CHRISCAM
Norm, no offense, but that line of reasoning is flawed too. A given transmission and rear end, as used in my hypothetical chassis dyno setup, will require the same amount of torque to turn it at a given rpm, regardless of what the source of that torque is.
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As long as the load that it is working against never changes, of course. But are you willing to always use (to use the test example numbers) exactly 50 HP and 3000 rpm in your driving so that you could make 'absolute powertrain losses remain constant' a true statement for you and your driving?
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Using your analogy of a pallet being dragged across a shop floor with two dissimilar weights strapped to them is NOT what I was describing. I specifically mentioned using the same transmission and rear end assembly in both examples precisely so that it would keep that source of frictional loss in the assembly as a constant.
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You're missing the point. The amount of friction depends on the amount of force between two objects (whether they're gear teeth or pallets on the shop floor is irrelevant) and the coefficient of friction that exists between them when one of them is forced to slide across the surface of the other one.
What you're still not getting is that the forces between the gear teeth when you're transmitting 400 HP through them is much higher than if you've only got 50 to work with. And power transmitted is where the majority of the friction losses are coming from. Very little power is needed to simply turn the gears, this being why you don't need to be Superman to turn the transmission or the differential over at low speed by hand (you're not working against much load, so you don't need to be very powerful).
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I'm not saying that two different engines will have the same frictional losses in their respective rotating assemblies, I'm saying if those two engines (and my hypothetical electric test motor) were all mated to that same transmission and rear end assembly, that trans. and rear end would require the same amount of torque to turn them.
That, in my mind means that a given transmission and rear end assembly should, at least in most cases, provide a constant factor of hp/torque loss when paired to a given source of twisting force.
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Constant factor (e.g. 15%) isn't the same thing as constant amount (some flat amount of HP lost).
Try to avoid confusing the two.
One last try . . . if the absolute value of friction losses remained constant (like OP thought had to be the case), nobody over on M6G would be complaining about differential temperature warnings when they take their PP2 out to the track, there wouldn't be legal action involving GT350's that didn't get this cooling, and Camaros wouldn't have differential and transmission cooling systems either.
Norm