[c5blkvette]

Backpressure is caused by restrictions in your exhaust. e.g. catalytic converters, mufflers, piping, bends in the piping etc. Basically youwant to have a free flowing exhaust after your headers/extractors.

What makes/limits the most power is the backpressure at the exhaust valve just prior to it opening to release the high pressure exhaust gasses in the combustion chamber. This is where headers/extractors come into play.

The length of the header harnesses the pressure wave from the exhaust pulse. As the exhaust valve "slams shut", a low pressure pulse runs down the header at the speed of sound. When it hits the collector, the low pressure "splits" and runs back up all the exhaust runners.

The length of the exhaust runners are "tuned" so that the low pressure pulse hits the exhaust valve just prior to opening (at particular RPM points). If you understand basic physics, the greater the pressure difference either side of a valve, the higher the flow (and scavenging - another topic).

My recommendations (in order):
1. Buy a high flow catalytic converter
2. Buy a set of headers designed for where you want most torque (4-1 will move torque higher and give more power at high RPM, 4-2-1 will give better midrange). Headers need to be equal length.
3. Buy >2" cat back. 3-4" is not necessary for small cid N/A