KingJoseph

Hey, I'm a Nismo owner.

Here's the deal with exhausts: Any aftermarket exhaust will get you minimal gains over the stock Nismo. Think about this; the stock Nismo exhaust nets 18 crank horsepower over the base Z exhaust. The FI exhaust is advertised on their site as netting 20 wheel hp over the base Z exhaust. So, you'll get a few hp but it won't be as drastic as high flow cats or test pipes, which are a LOT cheaper.

As such, HFCs or TPs should be your first mod. They're only a few hundred dollars vs. over a grand for an exhaust.

All that being said, I'm a Nismo owner with an FI exhaust installed. If you go carbon fiber mufflers, you'll save a lot of weight over stock; the Nismo exhaust is a lot heavier than even the base Z exhaust. It's sprung weight, so it doesn't matter that much... but it's still nice to lose a little. You'll also get a beastly exhaust note that you don't get with the stock Nismo exhaust. Is a few hp, a little less weight, and an awesome sounding set of pipes worth $1600 (price of CF w/ 12" resonators and shipping)? For me, it was... for some, it may not be.

As said above, I'm of the opinion that the stock intakes don't need to be replaced; you can get a few hp on the cheap by getting post-MAF tubes and K&N drop in filters.

Honestly, other than that... the only other place you'd see sizeable gains w/o forced induction would be going long-tube headers instead of HFCs or TPs... but the cost (or difficulty) of installation makes this a significantly more expensive (or more challenging) prospect.

Hope this helps; I did a ton of homework over the last year on this stuff.

EDIT: Getting a tune after multiple bolt-ons would also get you good gains, but you risk voiding your drivetrain warranty. That was not worth it for me only having exhaust and HFCs; it may be in the future when I have less/no warranty remaining.