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!!
I'd read somewhere that a little back pressure would force some of the burnt gases from the exhaust back into the cylinder. I suspect this would have two effects. 1. Help heat the incoming charge, and 2. reduce the burn temperature of the new charge, since the exhaust gas has already had all of the fuel burnt out of it and would just act like inert gas.
Is this what you are talking about?
