Hi there I have a 09 Sierra 6.2 Denali AWD and currently have the mods listed below. Just wondering what kind of hp and tq would I gain going to 1 7/8 Headers and 3 inch collector. Thanks

Afe Stage 2 Si Intake
LS7 90mm Throttle Body
Corsa Touring Cat Back
OBX 1 3/4 LT Headers 2.5 inch Collector with Cats
Diablosport Intune Custom Tune by DiabLew

 

You won't gain much...money would be better spent on a cam upgrade, nitrous, converter, or 4.10s....

 

I disagree, OP you might might around 8-15rwhp more with the 1 7/8s plus gives you room to grow when you do a cam. Heck my buddy gain 11rwhp out of a NNBS "5.3L" doing the swap.

 

The bigger headers are better on that engine for sure... But not worth the money to swap right now. It is better spent elsewhere... If it comes time to make big power then swapping headers will be one of the smallest hurdles to get past.

 

I'd do a converter first .

 

Converter next, and a cam after that. Then if you still want a little more, 1 7/8" headers.

 

What about power say under 3500 rpm? Like ur DD power haha? Which would be better with high flow cats then straight through muffler. (1 7/8"or 1 3/4")

 

Although i dont frequent the site I have friends who do and over at camaro5 and there are back to back tests with 1 3/4" vs 1 7/8" headers. The differences were minimal at best

Even 2" prims havent shown huge gains unless you have big cubes? Spend money elsewhere

 

Heres a thread from tech

1 3/4 headers vs 1 7/8 headers my experience - LS1TECH

 

I have the same mods and have nitrous. It's OK, but I wasn't that impressed. I did fry my converter though, so i put in a Circle D tripe disk at 2600. I'm happy with that. It seems a little loose, but when i get my cam in there it won't. My truck is a DD and I do tow 8,000 Lb on occasion. Forget the expensive 1 7/8" header and get yourself a converter and cam with a good dyno tune.