[Raptor]

The less obvious answer may be the best on this, opening up the combustion chamber might net you a bit more power overall as well, the factory does a horible job of making the chambers equal and correctly located, they are quite a bit off on every head I have checked. The valves are also pretty well shrowded. You could probably cure all these problems in one shot ast well as cleaning up potential hot spots etc. Not the easiest answer, but probably the best overall for improving things.