I am just finishing putting a stock 04 gto LS1 into my chevelle. A buddy got me two dynomax mufflers that are 3 in / 3 out for free. I have searched a lot and see the true dual consensus is 2.5 for a stockish LS1, but are there any drawbacks to running 3"? I am running hooker headers with 3" collectors and at best eventually plan on going with a mild cam/heads. Thanks.

 

Well if your considering going with 3" due to free mufflers then count that out cause your gonna pay more for 3" piping.

As far as 2.5 vs 3 i prefer 3 for room to grow even though true dual 2.5 is enough for around 500hp if i remember correctly. You shouldnt have any drawbacks to 3".

I am running dual 3" on my mustang with a cam and donmt see any drawbacks whatsoever.

 

Thanks. My main concern was that I had heard there would be increased drone due to the larger pipe. I am building this as a daily driver and don't want it ridiculously loud at all.

 

Larger pipe equals slower exhaust velocity all things equal.
Just run 2.5 tubing to the muffler and expand at inlet.
Maybe throw in a resonator before the muffler.