Some engines are advertised as being schnuerle ported. This means that there are multiple (usually three) bypass ports in the cylinder which allow fuel up into the combustion chamber. On a non Schnuerle ported or "loop scavenged" engine there is only one bypass port which is opposite the exhaust port. This may result in some of the fuel passing over the piston and right on out the exhaust port. With schnuerle porting the fuel arrives from different directions and converges at the center of the cylinder which allows more fuel to be burned, hence more power. Most newer engines use schnuerle porting.

Another way to tell is to look on the side opposite the exhaust and look for the "bulge" if the side is flat so to speak then it is Loop scavenged if the bulge is there, like the left engine in the picture, then it is Schnuerle ported.

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