I'm building a ls1 iron block 6.0 standard 4.00 bore right now. I'm putting a set of ls3 heads on it with 2.20 1.60 valves. As it measures right now I have a 1/8 of an inch between to walls and the valves. I do plan on boring my block .030 over but that's not gaining that much more room. Is the a rule of thumb when it comes to cylinder wall valves distance between the two for turbo applications. If so I'd like any input.

 

No real rule of thumb per se, but more room equals less shroud. Less distance won't hinder your engines' performance, it just won't maximize it...