low back pressure is good in some cases and bad in others, it you want low RPM performance then you want a little more back pressure, if you want High rpm performance you want less B/P, the reason is that low rpms need to use velocity to get the exhaust out while high rpm doesnt in really kind of just pours out so high flowing exhaust works really good. That is why you should always match the flow of you compnents such as your intake, throttle body, intake manifold, cylinder ports, cam, header/manifold, cat, and catback. so really it matters on what your motor is set up to do. :wacko: