Curious what is everyone's opinion on the max HP before it gets too restrictive. I have them on a 400hp and wondering if long tubes with a 4" be more beneficial than my 2055's with 3" Gale Banks.

The collector hole is something like 1.9" on those. They need opened up to 2.25" or so before getting into the sealing surface of the ball flange. 2.25" is minimum needed for something like 400 hp. Longtubes or other shorties with larger collector would show decent gains imo

I would add to Orr's comment as well.

2.5" minimum for dual exhaust, or a single 3.5-4". A single 3" exhaust is rated to about 365hp. You could figure out the math which is what I did. Im going to be making 550-600hp on a supercharged 5.3LS. I had dual 3" which would be perfect but I wanted something more stock looking. I decided to go with dual 3" from the collectors to flomaster merge ypipe dual 3" to single 4", then made my own 4" catback. Single 4" should flow slighly less than dual 3" but since there is less surface restriction/friction single exhausts tend to loose less flow compared to dual setups.

Given your 400hp your single 3" would be a restriction... how much prob not horendous but worth an upgrade so you loose less.

Go BIG or go home.

<--- LTs

Thanks for replies. I did try to open up the collector area, but it does seem to be small to produce adequate air flow for 400HP.

I think LT are in my future along with a 4" exhaust. I'm budgeting now for a T56 so I just need to see if the LT's will clear the Hawk's Crossmember. I will contact Hawks to find out.

I have cars out here making over 400 to the rear wheels with my headers and dual cats and 3" to the rear.

Dyno Don, thank you. Sent you a PM