[NomadTW]

open headers is not as good as running a straight pipe. cut your exhaust off at the axle... then test it out...

with open headers you will loose the scavenging effect and all of the exhaust gasses will not be pulled from the engine in time for the intake stroke and exhaust gasses will be pulled into the combustion chamber... there is less oxygen in exhaust gasses than in air.. duh... this will hurt performance
back pressure is bad yes... but exhaust flow velocity for scavenging is very very important