What is the top speed of a 50cc engine?

The speed of the engine is defined as the maximum revolutions per minute of the crank, which would depend on engine design. 50cc chainsaws can rev to over 14,000rpm. The maximum speed of a vehicle with a 50cc engine would depend on its weight, the gearing, the fuel and the environment it is being ridden in. It is possible to tune a 50cc engine in a motorcycle to go over 100mph - but at the cost of engine longevity.