I have an LQ4 engine with ported 243 heads, a comp cams 226 I 234 E 600 lift, TBSS intake manifold with 90 mm throttle body long tube headers going through 2 1/4 inch pipes and turbo mufflers. I think I need to step up the pipe size to 2 1/2 in to 3 in it's a true dual system no cats. It only made 362hp and 364 tq at the wheels. I think the exhaust might be holding it back what do you guys think, power peaked at about 5,500 to 5,700 feels real strong though almost can't even use it on the street but I thought I would have more also the converter was unlocked during the pull.

 

I'm basically running the same setup LQ4 243s ported and milled .030 by AI 226/230 cam TBSS intake 92MM TB im running crush bent 2-1/2 pipe true duals with flowcraps.

truck put down 410RWHP 390RWTQ my tuner said its got more in it but the tranny didnt like the 3rd gear pull to 140 locked so he didnt wanta pull it any harder. BTW this was on a mustang dyno.

 

I'm running 3" duals and I'm pretty much stock...just got a modified intake, an X-pipe and a Jones Full Boar muffler.

If I can utilize that pipe size with a stock engine and stock tune, then you could definitely use a factory 6.0L 2500HD exhaust.