Re: Is it a Looper or a Crossflow
Loop Charged motors can be more fuel efficient and more powerful, due to the better exhaust scavanging of the loop charge design. A cross-flow motor has a single transfer port. Loop charged motors have multiple transfer ports up to 4 or perhaps 5.
Any style 2 cycle motor (cross flow or loop charge) can be designed to be more or less fuel efficient. This is due to the need for fresh fuel to sweep out the exhaust gases. For max power, sweep out all the exhaust, and some fresh fuel goes out the exhaust as well. Less power can result in less fuel use.
High performance 2 cycle motors were perfected in the 70s single cylinder motorcycle engines. They were 7 port loop charge motors with reed valve induction and expansion chamber exhaust. These kind of features are hard to have on a multicylinder compact motor like an outboard. Outboards adopted as much as was practical.
For example, e-TEC motors have a loop charge design with a dual length expansion chamber exhaust. Exhaust is tuned at two distinct RPM ranges, for best power and economy. This dual expansion chamber design is operated by opening an closing a door in the exhaust passages. The late 90s and newer 60*V6 Johnnyrudes have a single length expansion chamber, based upon the e-TEC design.
