Originally Posted by JoeNova

The problem comes from the guys with small cam 4.8s or stock cam 5.3s running 1 7/8" race headers with a 3.5" collector and dual 3" exhaust complaining about lack off performance when they mash the throttle at cruising speeds. Lots of noise, but you don't really go anywhere.

Originally Posted by thunderstruck507

Agreed on all points with further clarification that I would not have any qualms about 1 7/8" on a stock ls1 or modded lq4. I'd say chances are high the op is using a 1 3/4" primary longtube.