Depends what type of vehicle and what type of track you're running on. I'd a 053 type of pipe for all around power or JP1 for a technical track or a 086 for a smooth big track with long straights. The latest batch of 7 ports come with an extra shim to be added for 30%. I've used RB C6 shims in the past and they fit pretty well. I'd assume shims for other motors with similar bore size should also fit.