I can personally certify that Stillen products make HP. On my old '08 coupe I went from 264hp bone stock to 285hp with Stillen CBE, Berk HFC, and Stillen Headers. I didn't see the gains advertised, but they added some ponies. Search the forum for TONS of dyno's and reviews of most of the products out there. Theres a lot of knowledge already covered here since the g37 hit the shores so many moons ago

 

Good choice. I don't know too much about the invidia exhaust. I do know the FI test pipes are a good buy. Your car should awaken nicely.

 

I think it's ridiculous to assume that an intake or exhaust will yield substantial performance gains simply due to an increase in airflow.

Furthermore, I question the appropriate "tunes" that some of the tuners are coming out with. The main problem is many tunes are done on inertial dynos which cannot simulate enough load (grams of air per RPM) for a 3500-3800 lbs car due to basic physics (and the lack of an eddy current). At less than "standard" load the car tends to run rich across the power band in open loop. Tuners then get an immediate hard-on and throw in some timing while pulling fuel across the board. Naturally the car makes "big power". And the moment you pull the car off the dyno the car runs like a champ insanely lean while causing occasional detonation causing your ECU to modify the base map to a safer condition - there go your gains.

Bottom line I haven't seen intakes, exhausts, and tunes make good, SAFE & RELIABLE, power. Keep in mind I'm in cali with 91 octane summer formulation. 100 octane is a different ball game.

 

Substantial's a pretty relative word. You can however make a noticable improvement to performance, looks and sound by doing so however. 10 months of smooth operation here and have datalogged AFR in mid 12s across the band WOT with actual load, wont be going back to stock ever as I'm sure you'll find most that have done the above would confirm.