Originally Posted by Jason Short

In short, yes But, I understand how it's easy to draw that conclusion since everything after your Y-pipe will still be 3" in diameter.

I gained 8rwhp with my custom Y-pipe (Flowmaster merge) over the stock Kooks Y-pipe on my H/C LS1 combo a few years ago. I'm sure the gain would be more like 10rwhp ALONE from the merge on a FI car. And, I still had a 3" catback on my car (SLP dual/dual).

Any time a fluid (air/exhaust in this case) moves through an orifice, it incurs losses from bends, turns, merges, and even through a strait pipe. In this case, cutting a hole in an existing 3" diameter and essentially jamming another 3" pipe into that one at almost a perpendicual angle is VERY inefficent.

Also, if you do go this route, it's also important to reduce the 4" outlet to a 3" over a distance. The 4" to 3" reducers that reduce over 1" in distance are not optimal. A reduction in diameter over 4" in length would be much better.

Here is a link from 'tech with some good reading: http://www.ls1tech.com/forums/genera...er-y-pipe.html

Hope this helps.

Originally Posted by Injuneer

With 614 rwHP, I'd think the 3" Borla would be a significant limitation. Why not a 4" Mufflex catback? I had Mufflex build a custom 3" Y-pipe using the Flowmaster 2x3->4" merge that Jason mentioned, and then continued back with the 4" catback. The only reason I switched to duals was because the Gear Vendor O/D unit interfered with the Y-pipe, and the Mufflex catback weighs a lot.

http://www.injuneer.com/images/photo...t/TADS4in.jpeg

Funny.... everything in that 11 year old picture is gone.... ACPT CF D/S, early Spohn torque arm design, Mufflex Y-pipe......