I have an 03 G35 6mt
70k miles
-Motordyne 5/16 spacer
-Muffler delete with resonated test pipes
-Stage 2 competition clutch
-Intake

 

What would you be looking to get out of by tuning? Are you willing to spend $600-700 to achieve your goals? Those are questions you should ask yourself before making your decision.

 

Power plants are like fingerprints, each one is specifically unique, the ECU does it's best to accommodate all the various modifications but at the end of the day it's whole purpose is to maintain a set of parameters designed to keep the engine within factory spec which focuses on longevity with a HUGE safety margin. A proper tune basically matches the ECU to the exact fingerprint of the power plant, removes a small amount of the safety margin layer (still perfectly safe since stock components can handle quite a bit more duty than stock tune) and the tradeoff is a sizeable gain in overall engine output.

The big question to ask, is it worth $600-700 to add 15-20 whp? Personally I would do a high flow cat / test pipe and THEN tune.