My buddy is looking to do some EXH work on his 98 GMC Sierra w/ the 5.7 Vortech.

No emmissions requirements here. Need info on Catbacks, LT's Mids..

Sites?

 

To the moon Alice! TTT!

 

What modification to it?

Doug Thorley Tri-Y headers are popular, they are mid-length.
If it's naturally aspirated with bolt-ons you might consider Hooker Comps. These are long tube (not balanced) and have 2.5" collectors. Natrually-aspirated L31's need some backpressure. Use dual 2.25" pipe or single 3". If you're shifting above the stock 4800RPM shift points consider dual 2.5" pipe instead of 2.25"

If this engine has headwork (springs), cam, forced induction and/or nitrous oxide, use Hooker Super Comps. These have larger primaries, they're balanced, and they have 3" collectors. These headers are thin walled so you will hear the exhaust tick. It's nice with a lopier cam but will sound kind of irritating with a stock cam. The exhaust will sound great overall with these headers because they are balanced and help smooth out the lumpy SBC firing order. For an L31 like this run dual 3" exhaust or single 4".

Talk him into keeping the catalytic converters. It's way too loud without them and these engines stink. It will get annoying in no time without cats.

 

i love my Thorley Tri-Y headers... with 2.5" duals. im running a 98 5.7L Sierra too

 

Im running Thorley headers with a 2.5" Magnaflow x-pipe to two 2.5" dynomax bullets and I love the power gain. I am planning on switching to Hooker Aerochambers though.