Originally Posted by ChitownM3
Doesn't make sense to me. I thought drivetrain loss was just a percentage, so if the engine makes its peak power at 8300rpm then it should also make its peak power to the wheels at 8300rpm. I did take a look at the RRI graphs and it does seem like power drops off at 8k rpm. But if you look at the OP's graph, the graph reaches its peak and then drops substantially leading me to believe they let off on the gas. I think the HP coulda gone up quite a bit more if they went up to 8300rpm.
Percentage implies a linear relationship between engine speed and loss. That is an approximation. I doubt that it is perfectly linear. At higher engine speeds lubricants behave differently (more heat to be dissipated), and friction losses most likely do not scale up linearly. I don't know this for sure though.
The power in the RRI tests peak around 7821 rpms--not at 8000 rpms.
It is possible that this was an acceleration test and they let go off the gas a bit too early. It would be good to have a few more data points after the peak to verify that the peak has indeed been experienced.