Bruce,

I used the LXCN35 Header Pipe Out - it just hangs out in the breeze at about the same angle as the original header/muffler.

Re: the tuning effect... I'm not sure about this. Given the engine is only doing about 9-10 grand, I'd imagine a tuned header would have to be over two feet in length. The EX-502 is about 4 3/4 inches long.

I ride dirtbikes - one of mine for example is a 400cc 55hp (at the crank, at 9,000 rpm) four-stroke. These four-strokes typically call for an ideal header length of between two and three feet. These engines put their maximum horsepower at much the same revs as our four-stroke model engines.

One thing about the EX502 header that is significant is that it is very thin-walled compared to the stock header and has a much better looking bend - perhaps it flows better. It's actually a nicely made piece of stainless pipe. You can even clean the castor stains off it with oven cleaner and it comes up shiny as new!

No, I didn't try an open exhaust port - that would have been a good test actually.

Your observation about the engine "getting on the pipe" is on the money. With the 14x8 at 8800, the engine is only putting out 1.3 hp and is harder to "needle" accurately, whereas with the 13x10 on it, it jumps up to 1.7 in the space of 1000 rpm and is a breeze to needle.