How a Looper Works va. Cross-Flow

[THEFERMANATOR]

The short story is a crossflow uses ports directly opposed and uses a deflector shaped dome piston to direct the incoming and outgoing charges. Loopers use a flat top or nearly flat topped piston and uses the port locations to direct the incoming and outgoing air charges. Since loopers rely on airflow to move teh air where it needs to go, they are less efficient at low RPM's where air speed is lower. As teh RPM's increase though, air speed increases and allows teh porting to work as designed in a more efficient manner. Cross flow engines with there design utilizing the piston shape is more efficient at low RPM's than a looper is. Cross flow engines are normally used in applications where they need alot of bottem end torque and good idle characteristics like smaller kicker motors and such. OMC really changed the game when they came out with the first loopers, and revultionized outboards at the time.

Then there is the type of porting used in many chainsaws, but I won't even go into that one.