all of the after market heads are designed with a very high roof in the ports. this allows the so called short turn to have a lot larger radius, which makes the head flow alot better, the ports are all about raising them,and making the short turn less of a right angle turn.the problem with a series ,is that you often you hit water when raising port.takes lots of time ,welding and experience to get it right.lots of power is made by the head and a number of other things. a good engine, is a combo of a everything.to many to list.(been there done that) cheers ernie