pennys58

I was wondering if there were any sound differences between the 12" and 18" Dynomax Bullets. Is 3" exhaust too big? Should I go with 2.5". I am going to have heads, intake, cam, tb, cai, headers(LT), X-PIPE, 2 bullets....

Mindgame

It's going to be a bit quieter with the longer case and the smaller diameter.

Is 3" too big?
If you do a search on the subject you'll see that its been covered more than a few times. IMO, 3" is not too big for a ~400 rwhp engine. You will lose a bit of torque at low rpm but what you trade for is more torque up top along with more hp.
Alot of people I think miss the boat when it comes to modifying engines for more power. If your goal is to extend the rpm range of the engine (cam etc) then you are looking to build the most power in a specified rpm spread. In that case, you look to building power in that range..... anything out of that range is not very important because the sweet spot is just a downshift away.
Lots of confusion on this subject.

-Mindgame

pennys58

So, the 12" will be louder than the 18" then? I have read alot about this subject, that is why I was thinking of going with 2.5". The only problem I am having is finding Hiflow cats with a 3" inlet and 2.5". Does anyone have any idea on a universal cat with those dimensions. I have to pass emissions, so the proper kind is needed...what does air/no air mean? Thanks