Fixing engine friction torque

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LE torque data
blue: engine torque curve
black: current friction model
red: Heywood (1988) TFMEP model


As you see current friction model is massively overestimating friction torque (I remember running into this issue when working on my sim code). Current code opens the clutch when braking to work around this.

The tfmep model as measured for several four-stoke engines over a wide range of engine speeds at wide-open throttle, looks like this:
tfmep = 97000 + 15 * rpm + 0.005 * rpm^2

For engines with throttles, one would need to add another ~50000 Pa (0.5bar) to the first coefficient to model a closed throttle. I am not sure if it really matters though. The difference would only be noticeable at low rpm.

To implement the tfmep model we need engine displacement. I'll be going through our cars and adding it (cars without engine friction would have displacement zero)

[engine]
displacement = 1.8E-3 # 1.8l or 1800cc

Help is welcome, of course.