Cutterb17

I have a 07 ls2 manual with billy boat exhaust (pretty much straight pipe) with gutted cats I purchased some 2in long tubes with x pipe will there be a noticeable difference with long tubes coming from very small mufflers and gutted cats ?

PMPerformance

You made a mistake with 2” tubes, but long tubes are typically a 20-25whp difference .

Cutterb17

And how about to sound level difference

PMPerformance

2” is not ideal for a stock car.
Sound level will be about the same since your cats were already gutted. Maybe a smidge louder.

Cutterb17

only other thing I would do is ported manifold and cat 1 7/8 headers ?

PMPerformance

1 3/4 is plenty, 2” is fine, but overkill and you will likely leave some tq on the table

Whodamans

the cats make a HUGE difference in sound. It really surprised me. You wont notice much changing the headers, maybe a slightly different tone but for volume not much different esp if you are already straight piped.

MARSC6

1 3/4 or 2 the mustang is still likely to win

Cherokee Nation

Use 1 3/4" headers more power on the low end and sound bad ***!!

449er

I agree that the smaller tube headers would be better on the street with a stock engine