I will be changing out to a HFC on my 07 coupe... is it worth spending money on a new exhaust? Im happy with the sound of my stock and have heard that the Cat is were all the resistance is.... So question is HFC + stock exhaust or HFC + aftermarket exhaust and is there any info supporting HP gains with aftermarket exhausts?

IMO the hp gain u get from a hfc or a catback is very minimal. You won't be able to feel it.

In my experience, I could definately tell a difference with the HFC. It pulled harder up top and the exhaust sounds better to me. I have a stock setup with HFC

I gained 13 whp 12 tq going from stock exhaust + HFCs to motordyne catback + HFCs, and I definitely felt a difference. Biggest difference was going from my HFCs to my motordyne ART pipes, +10 hp +20 tq in the low end.

Those ART pipes do provide some unreal low end gains especially from a bolt on part.

Whats an ART pipe? Is it a straight racing pipe no cat?

im in FL with no emissions but might move back to NJ with emissions, is the cat easy to swap on the G or should i just go with a HFC over a track straight pipe?

^ yup, no cats.

https://g35driver.com/forums/intake-...art-pipes.html

https://g35driver.com/forums/intake-...art-pipes.html

No cat, but not quite a straight racing pipe either. Has shown some pretty ridiculous gains, not to mention a bit quieter than HFC's by all accounts. I'd pick them up for myself if they weren't so dang expensive.

Best bang for your $ w/b the HFC's! Then if you want more/different sound I'd go with a quality DUAL cat-back system from HKS, MotorDyne or Stillen. The single y-pipe back system costs less but the result is worthless. I like how the MD ART pipes look but I won't mess with the legality thing here in CA.
Gary