SpudFiles

hmm MC that does look interesting.. not sure how I am gonna fit that inside 1/2" fittings and pipe but that probably can be done

I've used a 1/8" NPT spark plug on smaller hybrid experiments, but do y'all think it will work for a larger (2") hybrid as well? I'd like to screw it into standard fittings in the back of the gun, but I'm afraid that if it's isolated in a 3/8" tee in the back of a 2" chamber, it won't ignite anything. Should this be a problem?

I've had very good luck with a spark plug on my 2" chamber on my hybrid.

I use an NGK CR6E plug, which is an extended plug with 10mm x 1.0mm pitch threads. I drilled a hole through the side of a 2 inch coupler and simply threaded it with a standard M10x1.0 tap. I also wrapped a little bit of yellow teflon tape around the threads of the plug. It's not as tight as an NPT plug, but it seals just fine at 7X pressures and doesn't leak at all.

I you don't have a spark plug, or want to use a pipe thread tap you already have on hand, I recommend this method: http://www.advancedspuds.com/nosparkplug.htm As jackssmirkingrevenge said, very tiny spark gap. The higher the "mixture" the smaller the gap.