Yes U can make a Generator out of a car engine.
But it is not advised. Coz the car engines are high RPM engines and mostly deliver there peak torque at very high rev range whereas the electric Motors(Altenators) which are comonly availabe in the market produce elecricity 50Hz at 1500 RPM So you can get electricity out of it but not 100%.
Like if you couple a 10KW Altenator to an 8000 RPM engine and run it at 1500 RPM you wont be able to get enough torque at this engine speed. So when you will try to put max power on the Altenator it will stall.
There is a solution to it but it is expensive. install a step down gear box for better performace. Idealy ur mehran engine shud rev at 4500RPM and the step down gearbox shud run the Altenator at 1500 RPM.
If U use a Car Diesel engine it will do a better job as Diesels are know to produce more torque at low RPM.
I hope U understand