3.5 vs. 3 inch exhaust

[Artworks]

I have been thinking of up grading my stock exhaust on my '95 6.5, as i want to get rid of the soot trap ( cat ) Local muffler shop says can install replacement down pipe , turbo muffler and 3" pipe for $425 (can. ) I can also get banks system , 3.5" out of DSG for $625 ( not installed ). Is the price diff. between the 3.5 and 3 inch really worth it ? Or do I bite the bullet abd get the complete Banks system with all gauges, pod, exhaust and AIS air box upgrade for $1200 ? Thanks all.

[DA BIG ONE]

I've gone to a full 3" system some time ago with some improvement. However, the real problem is the turbine housing outlet chocking the exhaust flow to the point of superheating the aircharge, elevating EGT's w/larger injectors and lower boost levels, and under high boost elevating IAT's, speaking of the GM-8 here which I have.

BOTTOM LINE: The turbine exhaust outlet requires porting to improve performance w/larger pipes.

Even w/o the need for turbine outlet improvment does the 6.5td (396+- ci)flow so much cfm under boost levels encountered w/average performance upgrades that it needs anything bigger than 3" I'm thinking no, but others need to chime in here with their thoughts on this.

[Kennedy]

My personal feeling is that 3 mandrel bent is marginal at getting good breathing and 3.5" is much better. A small shop will not have a mandrel bender so their press bent which is a waste of money IMHO.

[damork]

Artworks,

I know there are benefits in going to 3.5" exhaust over 3" exhaust, but you will have to expand on what your objective is. It seems to me if you want extra power between 2200-3300 engine rpm (maybe 20 wheel hp) and you pull a lot or need the power, then 3.5" is the way to go. If you look at the dyno results, the 3.5" exhaust shows rear wheel horsepower gains, but the bigger gains really appear to start at 2200 rpm.

I put a 3.5" system on mine and felt improved response and slightly cooler exhaust temps, but was more interested in economy and it never changed that at all over stock and I rarely go beyond 2100 rpm.