Hi Greg,

My experience and assumptions with glow, is likely misleading me in my conclusions. That's my story and I'm sticking to it. But somewhere in all of this, there IS the issue of ignition timing isn't there? On glow, sometimes you can get good throttling by reducing the CR with an extra shim or two, a real easy thing to do on ALL the Norvels. So if you decrease the compression, (on glow) you need to lean out the needle some and this, in turn, leans out the idle. This can help a lot if you don't have a means of adjusting the idle mixture. I regret not having any four stroke experience but any chance that the two, four stroke and two stroke, will respond somewhat differently to the items we're dealing with?

But here's what gets me about four stroke conversions. If someone had proposed the system as used on a four stroke conversion, I would have said, no way. Yes, it would work but the restriction caused by the small hole in the glow sized threaded portion would render the system unusable due to huge losses in efficiency. But not so, apparently. But has anyone just gone ahead and bored out and threaded that portion MUCH larger as in about the same size as the contra-piston that's used?

The noise? The Norvel conversions seem to have quite a broad range on the compression screw. You can back off to a real smooth, quiet run but at the expense of an available 600 RPM or more. Cranking in the compression, you immediately get a sharp tone that doesn't change much till it gets REAL hard and then it gets scary, something is going to break for sure. So I set it at about the middle of this range for the best power. In the air, I can say that the diesel version, on all kero is certainly louder than glow on the next size smaller prop. In fact, it's more like a purr than the normal scream of a glow. I DO have a muffler extension and that may be a factor. Dunno, all my .074s have this extension to clear the fuse.

And I do have the three other Norvel sizes to fool with. Bench running is just the start, they have to fly to prove their worth. Will get busy this winter building big stuff. The SMALL guys are gonna have a fit but hey, it's for science guys. But no,,, I'm just having fun.