Ok, I've heard alot of talk about back preasure... and I was under the influence that back preasure is bad... and you want a negative back preasure.... but my friend told me that you some back preasure for you low end torque applications.. anyone know anything about this back preasure myth?

 

lol, Trevor, I'm gonna save you some trouble and just tell you to search before you open one of the biggest cans of worms on this site. Trust me, you'll find plenty.

 

This has been beaten to death over and over again. To sum it all up, backpressure is bad. Like stated above, do a search.

 

Backpressure is bad. Period. The reason you don't see 4" duals on cars however, is not because of backpressure, but velocity. Huge exhaust pipes will have less backpressure, but also alot less velocity. The higher the velocity through the pipes, the better the scavenging effect to empty the cylinders. This means more horsepower and torque.

Basically, you want as little back pressure as possible and as high an exhaust velocity as possible.

 

Sorry bout that, didn't know everyone was so touchy about this subject i just wanted to know before i went and did anything stupid....

 

Well, pardner, you're new in these here parts, so we ain't gunna hold it again' ya.

The velocity part is really about the header primary tube size - keep it small enough to keep the velocity up but not too small to become a restriction. 1-5/8" primary headers are fine for most street-driven applications. 1-1/2" will be restrictive, 1-3/4" will slow down the exhaust at low RPMs and inhibit the scavaging effect produced by the velocity.

Once you get down beyond the collector, you just want to keep the stuff moving without undo restriction. But, as stated, at that point 4" isn't likely to do you any more good than 3". However, 2-1/4" trying to move that stuff on back is a different story.

Seems it all has to be repeated for somebody every couple of weeks, so this should take us into November.