Voltage of alternator depends from alternator regulator in other words from alternator model. It is usually 14,4V-14,2V on alternator, but on batterz terminals no more then 13,8V or you will have thirsty battery.
Without regler voltage goes to 15V and more, and voltage is related direct from rpm of engine and can go to 17-19V.
Also without battery voltage will have strong peaks up to 40V which can kill fine electronics in car.
If you whant better efficiency try newer car.
Can you please send me the link to the data sheet of some of the popular and easily available car alternators.
I dont think that this will not be from some significance, because you are from India, and I'm in Europe. I mean on "easy available".
All depends from car which alternator to use. I have in Golf 2 VR6 150A alternator (almost for welding :-D). But you cant put that in some car with weak engine like 1.1 or 1.3. You need power to rotate alternator, it takes in full strenght up several HP for normal cars (55-65A), you see what will happen with 120A or higher with smaller engine. There is systems for welding in field with alternators powered by small fuel engine, or car engine.
There is one other story about battery capacity in car. Should put bigger or smaller battery inside or leave it like factory. But this is just other story.
:wink: