What does 66/80cc mean on the 2-Stroke engine kit?

The 66/80cc refers to the engine displacement size. While we have chosen to use the long-standing factory branding engine size of "80cc", the true displacement of the bicycle engine is 66cc. Through the years, China bicycle engine manufacturers have advertised their biggest engine as 80cc, therefore we have listed them in the same way on our website. However, the bore and stroke of an 80cc being 47x38mm equal 66cc. Therefore the true displacement of the 80cc bike motor is 66cc. In the west, the volume of a cylinder is calculated by using the formula Volume = Pi x Radius Squared x Stroke. However, in the east, the displacement of an engine includes the area of the cylinder head's combustion chamber as well as the volume of the cylinder. Therein lies a discrepancy between measuring standards by the manufacturers in China with those in the United States. However, all "80cc" engine kits on the market today are actually 66cc in displacement size if measured by US standards.