Dave, on the Macs spec sheet it's calling for a 6" header length with a 12 x 8. Did I read it wrong somehow?

Right now the header is about 6.5" so going by the specs on the Macs sheet, I can shorten it about .5", change the prop back to where I was and tweak from there. I'll probably have to richen up the low end since we did lean it a little too.

I'll give a Zinger a go. I think I have one back there but I'm not sure what size it is.

Maybe I'm not hearing the engine right but I'd swear when we ran it on the ground, you could hear it "hit" on the pipe. Not sure what rpm is was at but man, you could hear it jump at a certain throttle level.