Originally Posted by earlwb

Yeah I was thinking you might have to go with a big cartridge like a 458 Winchester Magnum or a 460 Weatherby cartridge, in order to get the volume up. But then one could spin the neck down some or make a plug to insert into the neck too.

It may work just fine for you. I think you ought to try the 300 WSM cartridge out and see what happens. I am running a old Enya 1.20R with a straight pipe or tube on the exhaust. It is crimped on the end and has a bunch of little holes in it. The engine doesn't seem to be bothered by it. Four stroke engines are not all that sensitive to the exhaust setup like two strokes are.