How can I control craft or Parts when cockpit is disconnected?

Ok so I wanted to do a drag race b/w my two vehicles so I added one on my sub assembly list and placed it on a build side by side. And connect it with a detacher. As I expected and experienced from my "muv 100 with drone" build, jet engine power, control surfaces can be controlled after it's detached from cockpit, I've also noticed brakes and wheels (turn) work after crash and when detached. But when I fired up the level and detached cockpit part, the engine (car engine) sound stopped and didn't worked. So I guess some parts/ controls like wheels, control surfaces, even jet engines, pistons, hinges etc works when they got detached but some parts like car engine, guns and weapons don't. So basically that's what I want to learn more about.

Is there a way to control parts when cockpit is detached like if there might be some trick or script like disable when group is deactivated etc? Please help me.

Also let me know if there's an easier way to do this drag racing thing.