seems like theres a variety of various PV designs. honda,yamaha,kawi,suzuki,ktm all used something alittle different. the only one im familiar with is ktm and it works pretty good. the main port is 67% of bore width which isnt far off from what you would expect to see on a nonPV port. of course you could make it even alittle wider if you wanted. getting to 70% probly wouldnt be a problem. so not all pv engines have narrow main ports. is cheetah guilitine operated by suction from the crankcase ?