Finally made time to do a speed test.
As part of my milling chain comparison tests, I've been doing timed milling cuts on a 12.5" pine cant.
The saw had been previously tuned by ear to 13,500, where it was still blubbering. It didn't clean up until 14,000+.
1st pass, 3/8 lo-pro milling chain. 0.76 inch/sec. Seemed happy running 10,400 RPM. About 6 feet into the cut, the engine bogged. After idling for a couple of seconds, it was willing to resume cutting. There were two big knots at the location where it bogged.
I was paranoid that the saw might have overheated, so I retuned to 12,000 RPM before the next cut.
2nd pass, 3/8 lo-pro milling chain. 0.76 inch/sec. This time it only pulled 9500 rpm -- yet the cutting speed was exactly the same ! ! ! Once again, it bogged about 6 feet into the cut. Once again, I let it idle for a couple of seconds and then it was willing to resume cutting.
I had planned to make a couple of passes with 3/8 x 0.063" milling chain, but canceled that due to the mysterious bogging problem.
Here is how the same lo-pro chain did with other top ends:
popped & ported BB -- 0.76 inch/sec
popped & ported OEM -- 0.73 inch/sec
stock BB -- 0.69 inch/sec
Despite the stalling problem, and the rings failing to seat well, this top end still holds my current speed record with lo-pro chain.
I'll let it cool down, take another compression measurement, then this top end will come off and the jug sawed in half so I can examine the funny lines near the top of the cylinder.