The guy ,Jeff Nance, that does my dyno tuning , told me to go with either a duel 3" or a single 4" exhaust system. ( for forced induction ). I gained hp and torque with the duel 3" exhaust , even before I put the supercharger on. You won't loose any power with a larger exhaust sys.,even N/A. put a BIG one on there.
Ron

 

I belive higher exhaust velocity compliments low end and staying on the smaller side could be better on a heavy vehicle ...There is probably a sweet spot for everyone depending where you motor makes most of it's power..I gained 1/4 second back in the 1/4 mile going from dual 2.5's back to a single 3'' with a dual 2.5'' y-pipe. Many others in the Titan community have found this out the hard way also. On my truck the topend gains were not worth the low end lost. But that was natually aspirated. The intake runners are longer on a Titan maybe they are just better tuned for each other..I can't use a dyno on the lowend end stuff since it only reads past 3.5k rpm on my 5 speed in 3rd. Seat of pants judgement and 1/4 miles times work better for me when tweakin an exhaust. ..I will go with back to dual 2.5's w x/pipe after the S/C is setup since my long runners are being replaced with a new manifold on the S/C kit... I will 1st do some dyno pulls and 1/4 mile runs to see where i'm at before opening her up some more...

Just my .02 cents...

 

i feel that the more open the exhaust the better. i have proven on the dyno and on the track that open headers gained 15rwhp and 20rwtq across the board over my dual 2.5" exhaust thru high flow cats and dynomax bullets. at the track i gained 2-2.5 tenths with open headers, and my 60' was the same if not better on occasion. as soon as i get my tranny finished, my exhaust will be the first thing i change. probably going to dual 3". this was N/A.

 

For me: ASM headders with custom 3" collectors, 3" metal Substrate cats, 3" X pipe, dual 3" (by 18" long) Magnaflows, side exit.

 

i have dynatech's with their y-pipe (cats gutted) going into a 3" spintech and two 3" out all the way to the rear. I just replaced the spintech with another spintech, single 3 in and a single 3 out. So my system is single 3" all the way out. I notice no difference from before and after of the dual and single.

 

How do you like the sound of the Spintech? I actually considered them.

 

i have the spin tech and then an aerotubro muffler (too help with some rasp). They sound good at first, then ya notice some rasp. if you dump the exhaust (i had a cutout right on the old spintech) right after the spin tech they sound great!!! maybe it's the length that makes them raspy.

 

i cant really see any point in putting a larger diameter exhaust than the collector size on your headers/exhaust manifolds, but if im wrong someone correct me with a reason

 

you mean one collector or both added together? I think mine are 2 1/2", combined would be 5". Yeah, anything bigger than 5" is worthless IMO if that's what you are saying.

But I am sure enough enigeering types on here will chime in to tell us that in forced induction, getting rid of the exhaust in a quick and restrictiveless manner is optimal. So, bigger the better in theory. Less restriction on the exhaust side of the engine.

 

A single 3.5'' would flow the around the same as dual 2.5's...A single 5'' is way out of control...