back pressure?

now i know that when you add a free(r) flowing exhaust you lose backpressure, which in turn kills torque. but i cant get anyone to explain how it kills torque.

now i know that when you add a free(r) flowing exhaust you lose backpressure, which in turn kills torque. but i cant get anyone to explain how it kills torque.
this may shed light on the subject
http://www.flowmastermufflers.com/backpressure.html

now that helps. i have a 4 2 1 header, and i keep hearing about loss of back pressure might make the car run crappy. and i didnt know if the computer could compensate. or if i would have to buy a different cam.