This is the O.S. Max .55 AX Aircraft Engine with Muffler. Advanced Bi-Metallic Liner process uses a double layer of plating material rather than one thick layer. This helps the metal bond to the cylinder and makes the plating more durable. Also, the plating process is more consistent, resulting in a more precise fit between piston and sleeve for better compression and longer life. Includes: O.S. Max 55 AX ABL Aircraft Engine with E-3070 Muffler, 40J carburetor, #8 glow plug, illustrated instruction manual, 3.5" (90mm) long needle valve extension cable and two 3x35mm muffler screws The large-chambered muffler reduces sound without reducing power. The 40K carburetor includes a diagonally placed needle valve so there's no need for a remote needle valve.