I am installing my turbo kit next week. I did not buy an exhaust yet so i am getting in dyno tuned open downpipe. Now my question is, if i get tuned with open 2.5" downpipe then i put on the N1 exhaust system in a few weeks will it need tuned again?

 

If the exhaust is a true 3" with no cat, you should be alright without retuning. The boost might get lower with the exhaust on it from what you were tuned at by 1-2 psi at most. The worst case scenario is that you'll run a little bit richer than when you were tuned.

 

Well the downpipe is 2.5" and the exhaust will be 2.5" with no cat just a resignator and n1 muffler. I will be running low boost. No more than 9psi so if i loose 1-2 psi with the exhaust that will make a difference in performance i would think. Could i safely turn the boost up like a pound after i install the exhaust?