The rule-of-thumb is that you only need a tune if you make both intake and exhaust mods. The ECM will usually compensate enough to protect the engine if only one side is changed. However, many people think a tune is well worth the time/expense - even with no mods - due to better throttle feel, better shifting, more power, etc.

Agreeing with that bro up there ^ i recently got my exhaust installed and honestly didn't even think of getting a tune just for that. I know an aftermarket exhaust is more than just for noise, but I dont feel the need to spend on a tune without completing the bolt-ons I/H/E first. after i get some Stillen air intakes, then for i would probably start looking into a tune for sure (I don't plan on changing out the cat's, just yet).

A tune seems almost necessary for Nismo's after upgrading both exhaust and intakes. After I installed my exhaust, last month, all was fine. However, a few weeks later I installed my Stillen Gen 3 intakes and the car started going limp mode after every WOT. Turns out that the Nismo's are tuned pretty lean from the factory with OEM parts. Without a tune to compensate for the parts, I was relegated to eco-driving. Now that I've begun tuning with Seb, all is well and so much fun!

Mine was rich before tuning.

^^^ What he said...I have the Nismo R-Tune intake and FI resonated high flow cats (on an IPL which is basically the Nismo tune, 348hp). My a/f ratios were off the charts when I was logging them with OBD Fusion. So I went to the dyno just to see and use their wideband and sure enough, I was in the 9:1 ratio by redline! Super rich after 5300rpm.

Intake and FI RHFC's were my only mods. Car ran and felt strong but definitely needed a tune which made quite a difference. The intake has the "inserts" to keep the airflow identical to the stock intake where it's approaching and flowing around the MAF's. For tuning, those were removed.