Re: Is the 4 cycle fuel conomy better than the 2 cycle?
^And the trend I see is a slight advantage to the 4-stroke at WOT and a moderate advantage to the 2-stroke at low speed. Perfectly consistent with what you would expect based on the mechanics of the two engine designs. The 4-stroke operates at higher vacuum at idle and slow speed, resulting in higher pumping losses and lower efficiency. At WOT the 4-stroke pumping losses nearly disappear but 2-stroke still needs to use crankcase pressure to scavenge the cylinders, giving the 4-stroke the edge.
Both of these issues have possible solutions. Application of stratified charge direct injection to the 4-stroke would reduce or eliminate the need to throttle at low power, while a turbocharger could provide "free" external scavenging to the 2-stroke, although some type of belt or electrically driven air pump would still be needed for starting and low power operation. External scavenging would also enable the use of a non-consumptive oiling system.
