These tests show the effects of a poorly designed expansion chamber on a KDX 200 grass kart motor. The blue line was the original pipe, which was a nice fit on the kart, but lacked any scientific design.

The red line was the run with a correctly designed expansion chamber and silencer.

Gains like this are spectacular, and totally transform the kart.

These tests are also from an (86) aircooled KDX 200 powerport motor. The red line is the stock motor with standard carb and exhaust. The blue line shows the same motor with a custom chamber and cylinder head mods, plus rejetting. The black line is the same motor with the barrel lifted 1 mm and the cylinder head squish band re-set.