You want a 4 mil no matter what. Don't mess with a stock stroke serval . Here's what I would do if I were you. Get a 421 serval and run it with the pipes and carbs you have now. When you get bored with the power your getting throw a set of pwk35s on and some shearer's, Cpi, rockets, R2s, or snipers. Then after you get it tuned good kick yourself in the ass for not going with this setup in the first place! Lol