I'm about to get my car tuned and dynoed this week but I'm also getting a new 2.75 inch exhaust compare to my 2.3 (right now) in the next few weeks. My question is can I tune it now with my 2.3in exhaust or will I have to retune it again when I get my bigger exhaust put in?

 

you should wait till you put on the new exhaust. Due to the diameter of the new exhaust your spool characteristics will change as well as your AFR. If you tune now with the your 2.3 exhaust, you could possiblily be lean with the new larger exhaust.