Attempting (perhaps vainly) to get back on track:
Define: "short cone". To answer the follow-up question: Yes, I will do it. Tell me when you need it.
Well, when I wrote it I just meant something that would be better than the slight flare, i.e. something just adequate to optimize the tuning with minimum effort. Of course, if one wanted, a much bigger cone could be designed that would make the engine more compact and reduce the lockup ratio to say, 5:1. But that would be a BIG cone. The advantage would be that we would have test data for an engine that someone might actually want to build! Not big enough for a kart, but certainly enough for a lightweight bike or trike if world-beating performance wasn't an issue. It's just that now that we have weeks rather than days or hours, it seems a shame to settle for a non-performer out of such a big motor and so much effort already expended. Greg, I think we three need to reach a consensus on what we want. And Greg, you set the target date, somewhere reasonably far out. I can fairly accurately build about anything we need for the tail end.
Greg, I think we need one more kind of test -- Collins sensors. What you would do is drill a 7/16-inch hole where you want one and weld on a 10Mx1.0 nut. The sensor is a CM-6 spark plug, with the gap left narrow as it is right out of the box. You bring off a low-voltage wire connected to the positive side of a 9V battery; the negative side goes to ground THROUGH a resistor -- try 1000 ohms to start with. What happens is, with air there will be zero current across the gap, and zero voltage drop across the resistor. As the gap is filled with ionized gas, current increases and a voltage drop appears across the resistor. You hook an oscilloscope or sampling voltmeter across the resistor to get the trace. What you're measuring is the rapidly pulsing degree of ionization. If this works, it would be a good thing to try out along the tailpipe; also in the intake and transition. You could use one at the front dome with the output going through a Schmidt trigger, providing a sync pulse to superimpose on the dynamic sensors, if the measuring rigs can handle that. (This would show you the delay in flame front arrival at every tested point in the engine!) You should at least try one in the tailpipe, to see if it will really work, and if the coming and going of the "cold air piston" can be plotted. I named this idea after Viv Collins, who originated it.
Greg, as to the observation of the left side of the chamber running hotter than the right side: Remember, on the right side you have all those little fittings and caps. Those are a considerable source of radiative heat sinking. There should also be a fairly large "cold" area on the belly of the chamber surrounding the weld zones of the vise mount lug.