let's see LCA means "lobe centerline angle" I don't really know how to explain its function because I'm just not good at that kind of thing, but I do know that the more cubic inches you have the overlap requirements are more also, up to a point anymore than what is required will kill bottem end torque for a 383 the optimum LCA is 106 degrees. The best advice that I can give you is to ready that book vizard is a genius when it comes to this kind of stuff and gives some awesome input on how to build a chevy from ground up. He also shows some trick stuff on how to port your heads and other awesome speed goodies.