I'm still trying to gather the parts I want/need to supplement my horsepower. Bang for the buck ( no nitrous ) seems to be a head and cam swap. My question is, most 5.3 litre heads that I've been looking at are spec'd for 3.9" bore, ls1. What are the implications of using say, Patriot 5.3/ls1 heads on a stock bore 5.3l? I spoke to tech at Patriot who, while assuring me that I can be accomodated with whatever I want, and tried to explain to me, seem to be speaking a different language. I actually understood very little of what he said.