Remember awhile back when somebody posted a pic of a factory long tube header...

[93GreenLX]

You need some backpressure. Don't want to lose too much torque.

Exactly why I recommended a 2" exhaust....I would say 2 1/2 is too much ...2 1/4 is possibly but probably pushing it

 

[bhuff30]

back pressure is bulls#!t. You don't need any backpressure, but you are going to have some, no matter what. The real problem that most people call lack of back pressure is actaully lack of exhaust velocity. As you increase the exhaust diameter, the velocity decrease. You need to keep the velocity up so that it the momentum to draw the next cycle of exhaust out of the cylinder. This is much more important in the header than the remainder of the system. I have a 2.5" exhaust, and several others do with no low end torque problems. Infact, even with thise big exhaust, and a cam, I am pulling the exact same 60' times on an auto which doesn't get above 3000rpm in the first 60'. The only thing I did to add low end torque was a little more compression (9.7 vs 9.0)