Model Engine Company of America
The Basics - 2 Stroke Principal
A two stroke engine must transfer the fuel charge from the crankcase into the cylinder. As the piston moves downward and the intake port on the crankshaft closes (see crankshaft rotation) the fuel charge is compressed. This fuel charge must be directed into the cylinder and accomplish several things. The attempt is to have the have the cleanest fuel/air charge for the next combustion. The remaining exhaust gases from the previous combustion must be pushed out the exhaust port by the incoming fuel/air charge. A clean sweep of the entire cylinder volume is attempted without any of this new fuel charge to escaping out the exhaust port. Port timing and direction are used to accomplish this.
Schnuerle Porting and the boost port
Named for its inventor, Dr. Schnuerle, these ports are two angled ports that focus the incoming fuel charge towards the back of the cylinder. A Schnuerle ported engine only has to have the two ports to be considered Schnuerle Ported. The boost port, the single angled upward third port, is not a Schnuerle port. It is an additional port to force the fuel charge upward into the cylinder.

Loop Scavenged. This the the original 2 stroke porting.

This example has holes in the lower part of the sleeve and piston. We refer to them as "cheater holes". They allow more air/fuel charge to pass through the piston skirt into the transfer channel and also cool the inside of the piston.

Fuel/air charge comes in on one side, hits the baffle and loops up to the combustion chamber then out the exhaust ports.

All loop scavenged engines have a baffle on top of the piston. Some refer to this as cross scavenged.

PDP - Perry Directional Ports
Perry ports are two tiny ports positioned on the exhaust side of the piston baffle. These ports direct a small charge of fuel/air to clear a small dead zone of exhaust gas. All Perry ported engines have a piston with a baffle on top.
Hybrid Modified Loop scavenged Schnuerle ports

Some engines use a flat top piston with a large boost port and small ports similar to Schnuerle type ports to direct the fuel charge back away from the exhaust port as the boost port is angled up to clear the cylinder post combustion gases.

Side note: The small grooves near the top of the piston are oil retention grooves. ABC engines have a tight fit so the oil film is easily wiped away with each stroke.

The above information is provided as a guide. Since MECOA/K&B has no way of determining the ability of the individual using and understanding this information, we assume absolutely NO RESPONSIBILITY for any damage to person or property from the use of this information.