forgive me if this has been asked before, but with dial up, hard to do the search, I didn't find what i was looking for. my 2 barrel on my 351m (78 bronco) is running like crap,choke not working and idles rough. i was either going to rebuild it or buy a new one. but my question is, if i get a 4 barrel intake and carb, do i need to swap out cam too? what difference will i see in mpg? thanks guys.