Q?turn car motor to genorator? Possible?

theres a power curve on engines, they operate best a a point along that curve.

then you have to take in to account torque vs speed.

when a load is applied to a generator its almost the same as a brake, hence the need for a governor.if you could keep a even load no biggie but thats not the case with a gen most times.

a car engine can be used but really your talking big energy, at least compared to most peoples needs. both in and out though less out then in determined by efficiency's.

any prime mover can be used for energy production either electrical or mechanical though practicality plays a role also? like anything its a give and take sort of endeavor, or in simple terms a balancing act.