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- Jun 30, 2012
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You can get substantial gains just by cutting the valve seats properly. The port SHAPE and down angle is important, what happens on a flow bench, might not be directly replicated when the motor is running. Norton was involved in racing developing single cylinder four strokes for about 3 decades. So the port shape in the Commando engine is probably already very near the optimum. If you modified it and it became better, you would probably be very lucky. - Joe Craig was probably not simple-minded.Below 3,000rpm it was difficult to judge either way, so my assumption is, backed up by riding it, that below that there really wasn’t much change. Hard to tell in reality of course, as when the throttle is opened, even from a standstill, 3,000 is past so quickly.
Above that there were substantial gains in torque and power everywhere. Biggest gains in torque were in the 4,000-5,000 region and the biggest gains in power were above 4,500. But there was more everywhere. Peak power was still same figure of around 6,250rpm which I found as a pleasant surprise as I had expected the point of peak power to increase up the rpm scale.
What was most interesting was to ride it back to back against my mates near stock mk111 (ham can, peashooters and EI being the only mods). There was just no comparison.
Do you think more down angle would be better, or is flow through both valves across the top, from inlet into exhaust at TDC, important ? It is on a two-stroke.