Mac Star 21 Engine an evolution of the Hyper 21, the MacStar 21 8-port is re-worked for improved performance. Now featuring a separate turbo plug head button and CNC machined blue anodized aluminum heatsink head for a leaner, powerful, more efficient engine with improved heat dissipation. In addition a MacStar 21 Pro version is also available and features a matt black anodized crankcase and larger rear bearing for better running and reliability, along with a larger diameter crank. Features: * Turbo plug for improved engine setting and performance * Separate head button * CNC Aluminium Heatsink head * 8-port piston and liner * 2.5 hp @ 38,000 rpm.