This is the Axial .28 Spec 1s Racing Engine with Green Cylinder Head, Pull Starter and SG (pilot) Crankshaft. Direct bolt-in replacement engine for any .21+ engine mount, also accepts most aftermarket shaft drive starting systems. FEATURES: ABC cylinder construction (Aluminum Bronze and Chrome) Composite bodied 8.5mm 3-needle Slide Valve Carburetor, factory reset line on High-Speed Needle and flush needles make resetting to factory specs easy SG (pilot) crankshaft with long duration intake Eight-port cylinder sleeve High volume transfer port design Removable button type combustion chamber Roto-starter available optionally INCLUDES: Axial .28 Spec 1s Racing Engine with Green Cylinder Head with pull- starter One Instruction Sheet One 8.5mm Restrictor One 8.0mm Restrictor REQUIRES: Glow Plug: Cold heat range Fuel: 20-30% Nitro with at least 18% Oil Content Manifold and Tuned Pipe (Depends on Vehicle) SPECS: Displacement: .28 cu in (4.6cc) Maximum RPM: 36,000 Bore: 18.6mm Stroke: 16.9mm Weight: 455g (16.05oz) Distance Between Mounting Holes Same Side: 20.30mm (0.799") Distance Between Mounting Holes Opposite Side: 37.03mm (1.45") Height Bottom of Mounting Tabs/Top of Cylinder Head: 97.27mm (3.83") Width of Mounting Tabs: 44.92mm (1.76") Distance from Pull Starter to Front Bearing: 83.22mm (3.276") Distance from Center of Engine to Front Bearing: 41.61mm (1.63") Distance from Center of Engine to Pull Starter: 41.61mm (1.63") COMMENTS: Some notes on Slide Valve and Rotary Carburetors: Rotary carbs offer a larger response in the middle of the power band. This works well for off-road applications when throttle response must be varied. Slide Valve carbs provide greater response at the beginning and end of the power band. This works well for on-road and racing applications for fast take-offs and high speed.