Dual 3" exhaust all the way out, ARH cats, Borla ProXS mufflers (4), 2 on each pipe- its not a restriction, you can see right through them.

 

Looks like you got that covered then. NNBS intake and a 90mm tb maybe would be my next purchase.

 

Just stay away from the FAST intakes, there are issues all over with them leaking.

 

Was JUST gonna ask about this-

My LQ4 is a 2002 and has the 75 or 78mm throttle body and opening- its pretty small.

So NNBS intake manifold? Looks like I'll need one of those. I swear I've read the LQ4 intake with the small throttle body handles 500hp? or 550hp?

 

They have. But every setup is different. I'd try a GEN IV manifold and some sort of 90mm TB... Either way around it's not gonna hurt the cause.

 

Busted a spare LQ4 intake out of the garage and did some minor porting, gonna see if anyone's got a spare 3 bolt throttle body laying around thats a 80 or 85mm unit-

depends on how large I can bore the opening out in the intake manifold (factory hole is 75mm behind the throttle body, tapers down to 73mm, then opens back up to 75mm when the cavity opens at the top). Like I said, IF it can be bored to at least 80mm, I'll stick the spare on it and go check the KPA readings to see if its gonna work. If not, I'll go grab a NNBS intake.

 

The LQ4 (Gen 3) intake and TB is done at 4000-4500 rpms on my 6.3 H/C motor. Don't waste time with it!

 

Yea you will see a great gain stepping up at this point... But i still think there is something limiting flow before the manifold.

 

First fill-up after mods, 9 MPG. Ouch. Then again, I have been romping it EVERYWHERE so I'd definitely say thats the culprit. No highway miles yet, haven't needed to travel.

 

Did you have any clearance issues with the headers? Are you stock suspension or key adjusted at all? Got pics?