This is the O.S. Max .55 AX ABL Aircraft Engine with the E3071 Muffler. FEATURES: Same mounting dimensions as the O.S. Max .46 AXII 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. Angular head design offers increased surface area for better cooling 40K Carburetor with diagonally placed needle valve eliminating remote needle valve placement Two year limited warranty through Hobby Services beginning at date of purchase INCLUDES: O.S. Max 55 AX ABL Aircraft Engine with E-3071 Muffler, 40K carburetor, #8 glow plug, illustrated instruction manual, 3.5" (90mm) long needle valve, extension cable and two 3x35mm muffler screws REQUIRES: Aircraft blend fuel containing 5%-20% Nitromethane with at least 18% lubricant SPECS: Displacement: .545 cu in (8.93cc) Bore: .91" (23mm) Stroke: .85" (21.5mm) Practical RPM: 2,000-17,000 Power Output: 1.75 PS, 1.68 HP/16,000 RPM Weight: 14.29oz (404g) w/o muffler w/ muffler Recommended Props: 11x6, 11x7, 12x6, 12x7, 13x6 Crankshaft thread size: 1/4-28 Distance from center of engine to drive hub: 2.4" (60.4mm) Distance from center of engine to end of crankshaft: 4.4" (112.6mm) Distance/crankshaft center to muffler exhaust outlet: 1.4" (36.7mm) Height from crankcase bottom to top of cylinder head: 3.6" (91.1mm) Height/crankshaft center to top of cylinder head: 2.8" (72.6mm) Width including mounting tabs: 2" (51mm) Width not including mounting tabs: 1.4" (36mm) Width between mounting holes same side: .69" (17.5mm) Width between mounting holes opposite side: 1.7" (44mm) Diameter of muffler body: 1.5" (38mm) Angle of muffler in relation to engine: 4° jxs 01/03/12 ir/jxs