When people do head swaps, what in the head makes the car run more efficiantly, or faster? for example, why do people swap h22 heads for an f23 head?

 

Well the one you listed for example is a DOHC head onto a SOHC body. So more power to be had there.

The "g22" h22 head on f22 body is used because the block of the f22 is cast iron (for boost) and the head allows it to breathe easier and get more power.

I'm not the best one to answer the question but that's the gist of it