diceco, I don't have specifics on me right now but the pipe i have was based on a design created with javapipe (http://www.mh-aerotools.de/airfoils/javapipe_en.htm) using port area and timings that i determined from the engine at the time. RPM was based on about 8K i think but it's doing more than that now. Un-silenced it really annoys the neighbors but there is no reason you could not incorporate a silencer on the end. Mine is very thin and pretty light, i fabbed the main pipe from an old stainless steel heater flue i had out the back using a mig welder and lots of tack welds. The heavy part is the header from the engine to the pipe. I tried thinner stuff but it cracked from vibration (although that was before i balanced the flywheel properly). My biggest problem is heat on the coupling between the header and the pipe. I'm yet to find something that will hold up to the heat.

Does it make a difference? Well I'm not sure! Perhaps i will stick a can back on it and give it a shot - i have plenty of them...

BTW, I had heaps of problems with the bolts stripping out on my engine so i used helicoils on the exhaust, head and carb manifold. Now it is really strong and i can use quality stainless bolts...

I'll take some measurements of the pipe tonight and post back.