First of all, "back pressure" is not a good thing for any engine. Google exhaust systems, and you'll find a boatload of info on the study of pressure and sound waves during the combustion process. NOWHERE will you find it stated, that in order for an engine to perform properly does it need some or any "backpressure" in the exhaust system. Engine designers spend many hours trying to find ways to eliminate any reversion or "backpressure" in an exhaust system, while still keeping the noise down to an acceptable level, or a level that meets the standards for epa, etc. With each explosion in the cylinder, first the pressure wave has to escape, followed by the sound wave. Exhaust designers tune the length of the header , size of tubing, collector shape, etc, to use the escaping sound and pressure pulses to help refill the cylinder with mixture. The only reason we don't all run around with open exhausts is the obnoxious noise it would create. Put a good header on that thing, and a GOOD muffler. Do the rest of the world a favor and keep it reasonably quiet. My 2 cents.