I have an old v8 laying around that’s not very useful to me. Is there a company that sells conversion kits that replace the alternator and starter with an EV motor? I can’t seem to find one.
I'm going to say no, though I don't actually know for sure.
I imagine any accessory belt driven alternator/generator/motor setup would have practically meaningless value towards torque or economy; limited by the friction available from the belt.
Edity edit: just saw your vid. Well call me Sally, there is something like that. Yeah, that belt had to be massively upscaled!
An alternator can charge a battery and run accessories, but given 1 horsepower is roughly 730 watts, you really need some high voltage system to keep the magic smoke in.
Edit: maybe we're talking different things. Honda used to integrate electric motors directly to engines in their early hybrids. Ford, iiiiif I recall, combine engine and electric power in the CVT transmission.
Both can use the EV motor as a massive alternator, but a standard alternator is simply too small, and attached to the engine too weakly, to generate the power of a hybrid.
And that's a system that was engineered end-to-end.
Developing an add-on is far more difficult.
Look at the aftermarket supercharger options for most any vehicle. Far simpler than this, and yet there are very, very few, with very limited engine platforms supported.