Right now I have an 05 G35 with basically most of the mods available minus the HFC's and headers. I have the Stillen Gen 2 exhaust which to me is pretty loud, but sounds good. My questions are...what type of gains would you see from each of these mods and what type of noise (loudness) changes would I see? Also, do HFC's allow me to pass emissions? I'm in Texas. Thanks.

 

hfcs will pass emissions

 

For the money & time headers are not worth the headache.
You get very little gains, HFCs are a better bet.
And yes you will pass smog with HFCs, but not with test pipes.

When you say most mods does that include a CAI, MREV2 & spacer?
Assuming you have the revup engine (spacer with nonrevup).

 

It's revup with CAI, plenum spacer, MREV2, pulleys,exhaust, and tune.

 

Should have added all bolt on's before your Tune.

Adding HFC/TP will alter you Air/Fuel Ratio. You'll run a little lean.
Def need a retune after more mods.

 

Ya typical...you say you're done with mods and get a tune, but then after a bit you start installing more. But I would get a retune. Any thoughts on the sound and power change from what I have now?

 

I have a injen ses and the notice sound wise was a complete difference. You stand behind my car and it sounds almost like a v8 when you rev it up.