Oh, and I wanted to add that YOU DO NEED SOME SORT OF EXHAUST SYSTEM.
Some folks think that open headers are awesome (and sound good
) but they really hurt performance until the exhaust pulses are often enough (read: high RPM) that there is no atmospheric pressure reversion into the collector or primary tubes.
An exhaust system CAN be too short and it CAN be too free-flowing. Don't get my original post wrong....I re-read it and can see where it might sound like I condone huge pipe that's only six inches long.
Unfortunately, tuning the exhaust is very difficult to do. To do it right, both pipes on a "v" type engine would have to be the exact same length and that's tough when both pipes run down one side of the truck. They should have equal bends (both angle and length) and we know that is impossible. There's always a compromise.
Jack, you're right, most aftermarket exhaust systems or custom exhausts are only for asthetics and sound....let's face it, if it doesn't sound bad-***, it probably isn't. Besides, factory exhaust is not visually pleasing. No disrespect meant to your last comment.
On edit:
The most disheartening thing I see when it comes to exhaust is the pipes people will have installed at an "exhaust shop". As a diagnostic rule, the new Chevy trucks are designed FROM THE FACTORY to have a backpressure to not exceed .5 PSI (one half of a PSI) of backpressure at full load redline. That is VERY LOW. It would be hard to beat that with ANY custom job. The factory pipes on the 2500/3500HD trucks with the 6.0L or 8.1L gassers are 3" and they go into a dual inlet/dual outlet muffler then "Y" into a 3.5" tailpipe that has nice, smooth bends over the rear axle. These people have the dual 3" Inlet/Outlet muffler removed and have two 2.5" pipes/mufflers welded in with tight non-mandrel bent pipe twisting all over the rear axle to avoid the spare tire. Under certain conditions, the backpressure in the pipes will actually cause a passive EGR effect (reversion back into the combustion chamber) and set misfire codes. UGH.
The exhaust from reputable companies (that our vendors sell) are good in the flow department and usually sound really good. Power wise.....maybe a little. But they do look nice with a polished stainless tip!