depends on what you have done. a cutout might hurt tq just a little on a stock motor but if you have a cam and all in it...the cutout should help some. ...unless you already have correctly sized exhaust.

I would go 2.5" on the 3.4 unless you have big plans for the motor....n/a or turbo.

 

With my inadaquate exhaust...ie crimp bent and only 2.25 the cut out (2.5 in flow from headers to cut out) I gained about 4 HP and 8TQ Again my exhaust was a mess! (with VERY MODDED 3.4) 3in mandrel bent gave me 15HP and 18TQ!

2.75 would be a nice choice, but I don't think there is a mandrel bent cat back system offered in 2.75! And 2.75 that is crimp bent is not better, probably worse then a 2. 5 in mandrel bent sys!

What I was told about cutouts by the dyno guy! He says if the exhaust system is sized properly and is made properly for the car (mandrel bends) You will see virtually no performance change with the car open or capped!

 

Did you guys have to make up some new exhuast hangers with the new exhuast. Mine hits the frame. Do they sell any I could use? I don't have any leaks, but I noticed that its very loud around where the Y pipe connects to the cat. Anyone have that issue? I was going to wrap some of that header tape on it, maybe keep it quiet seeing the car does not see any rain any more

 

On my Blazer, at "Y" pipe I discovered a point with very little welding, making my noise.
Upon removal of the "Y" pipe, I saw the dark exhaust clue of leakage.
A Friend weled that point for me, reinstalled "Y" and now is quieter, too.

 

I don't have a cat either so that could be it. I will have to check out my Y pipe sometime. Thanks for the tip. Any advice for the exhuast hitting my frame? The I pipe hits along with the right tail pipe hitting the spare tire well.