that info is in the header. You can alter values and it works just fine.
Examples:
mass=(1145.0) changed to mass=(1005.0)
throttle_rpm_ratio=(9622.2) changed to throttle_rpm_ratio=(3621.3)
antipitch_susp=(1500.0) changed to antipitch_susp=(2560.0)
CSINSIDE_ENGINE_REVVED=ENG2IC.WAV
change to CSINSIDE_ENGINE_REVVED=ENG2IQ.WAV
and add a wav file to the both the 22k and 11k sound directories.