Why do cars lose low end torque with open exhaust systems?

[MiracleMax]

A word on back pressure.... It sucks in any form.

Back pressure should be called what it really is. Negative torque pressure.

ba... I mean negative torque pressure is force the engine has to work against in order to expell spent exhaust gasses.

Ideally you want an exhaust system that has no back pressure without losing velocity or over scavenging the cylinder. This is the best system for a typical street car that has an engine that isnt optimized to take advantage of the suction energy created by a tuned exhuast system.

Now depending on how you look at things, this probably something equally wierd (as saying all back pressure sucks), but very small tube headers with a nice small dia exhaust (upto the mufflers) will do a good job.

by small I mean 1-1/2 primaries and 2-1/4" x-pipe (if you can find it), flair it up to 2-1/2 bullet mufflers then do whatever you want after that (2-1/2 inch pipe I think would work best, but isn't as important as the ego factor of big exhaust tips), if you can get the entire system thermal barrier coated, even better. The longer you can maintain heat and velocity in the system, the better it will perform.