[Psycho]

The key use of headers is to scavenge and to reduce the load on the pistons, hence allowing it to rev more freely.

Also the back pressure theory might hold true for most of the cars but on some engines there is a need for slight back pressure due to the cam profiles. The dia of the pipes can also negate the free flow principle by robbing you completely of lowend torque.

You can however run 2 pipes or 4 if planned right will defn improve performance. The easiest approach is to merge into one pipe and then redistribute it to 2 pipes, here one pipe would work as the collector thus causing the least of the worries.