I'm getting my 3" cutout put on today since i got it for some better gas mileage to college, and to be loud when i want to. Think it will help much with performance?
Right now i have Stock everything running into a 3" inlet with dual 2.75 outlets magnaflow Ypipe into a stock SS truck catbck.

 

I just put one on right after the y-pipe and before my magnaflow, Its not that loud with it uncorked. I didn't really notice a differnce, I'm gonna keep it closed up till I get my cam swap done, maybe then it will sound good.

 

I had around .15 sec gain in the 1/8

when you get rid on the cats and get headers its loud as hell

 

I gained about 1 tenth on the 1/4. Its loud, but sounds awesome, not overly loud at idle though. I have dual cutouts before my x-pipe.

 

I run about the same open/closed. I'm sure my gas mileage dive bombs with it open because of the low end torque loss, usually requires more throttle to get going.