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Originally Posted by tholyoak
This 15% number is always thrown around.
Let's think about it for a second. If I have a 100hp car with a 15% drive train loss. That means 15hp is lost to the rotation of components between the flywheel and the tires (friction heat etc), fine. Now I take the same car and drop in a 300hp engine, by this flat 15% loss method the components between the flywheel somehow now consume 45hp. Doesn't make much sense does it. I am open to suggestions as to how this is but it seems to me that the parasitic loss from the flywheel should be constant for a particular car and not a function of the amount of horsepower being produced.
My take is that the trend of comparing runs on different dynos is worthless, also trying to extract accurate flywheel hp numbers from chassis dyno numbers is also a pointless pursuit.
Todd
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The drivetrain you need to handle 300hp (really the torque is the determinant, but I'll go with hp since that is your example) will have about 3 times higher loss (versus the 100hp drivetrain) due to higher rotational inertia (heavier gears) and more friction (larger surface area on gears and bearings). Will it be a perfectly linear 15% at all hp/torque levels? No, but it is a pretty good rule of thumb that matches nicely with real-world data.