Starkweather, My comment about backpressure relates to a low compression street engine. Back pressure is necessary for the best flow of incoming charge, exhaust cycle on a 4 cycle engine. A stock or mild engine is designed with cam, valve lift and timing to run with some back pressure. Of course, too much back pressure would be bad,like a plugged muffler etc. A more radical engine with higher compression ,big cam lobes, bigger valves, etc can benefit from headers, big pipes to scavenge exhaust. I was just reading in Street Rod mag about the ford Y block running best with 2 inch pipes and glasspacks vs full flow mufflers and big pipes. Hope this makes sense, there is alot of info on this subject out there!!
