This is the O.S. GT55 Gasoline Engine with Electronic Ignition.
 

FEATURES:
Produces 20-30% more power than any other engine in its class
IG-01 Capacitive Discharge Ignition uses a microcomputer programmed for optimum spark advance through the use of magnetic sensors on the crankcase and prop drive, the IG-01 also detects and compensates for wet plugs to ensure consistent quick starts, also requires minimum current in stand-by mode and features a low voltage warning (intermittent engine operation)
Front mounted WLA-2 carburetor stays cooler for less heat percolation and more consistent performance, simple and direct throttle and choke linkages
Unique one-piece crankcase eliminates gaskets and enhances strength and precision
Front induction rotary valve crankshaft design for positive opening and closing of valve for optimum timing, no oil seal required which eliminates RPM loss due to additional friction
Massive front and rear crankshaft bearings for longer life and maximum power output
Thin high-performance piston ring and high-strength aluminum alloy piston for reduced break-in and high compression from the very first run
Two year limited warranty through manufacturer beginning at date of purchase

INCLUDES: O.S. GT55 Gasoline Engine with Electronic Ignition, carburetor, CM-6 Spark Plug, Prop Washer with four 5x40mm Socket Head Cap Screws, Exhaust Gasket and Instruction Manual

REQUIRES: Propeller: 22x8 for break-in
            22x10, 23x8, 23x10, 24x8, 24x10 for sport/acro/scale use
          Two-Cycle Oil: Break-In, Klotz Modelube recommended, mix at 30:1
            gas/oil mixture for 10 flights, 1.3 - 1.6 gallons (5-6 liters) of
            gas
            After Break-In: mix at 50:1 ratio, See COMMENTS below
          Muffler: See COMMENTS below
          Fuel: Unleaded regular gasoline (no need to use high octane)
 

SPECS:    Displacement: 54.9cc (3.35 ci)
          Bore: 1.62" (41.2mm)
          Stroke: 1.62" (41.2mm)
          Output: 5.5ps / 7000 RPM
          Practical RPM: 1,500 - 8,000
          Weight: Engine 1,580g (37.5oz)
                  Igniter 140g (4.9oz)
                  Muffler 6.28oz (178g)
          Carburetor Settings: Two turns out on high and low speed needles from
            fully closed position, then start engine and follow break-in
            instructions on pages 18-25 in manual
          Distance/center of Mounting Standoff Holes Top to Bottom: 2.6" (66mm)
          Distance/center of Mounting Standoff Holes Side to Side: 3.1" (78mm)
          Distance/center/Mounting Standoff Holes/Crankshaft Center:1.3" (33mm)
          Height/bottom of Mount to Top of Cylinder Head: 7.1" (180.4mm)
          Height/center of Crankshaft to Top of Cylinder Head: 5.5" (139.2mm)
          Width at Cylinder Head: 2.9" (75mm)
          Center of Crankshaft to Center of Exhaust Outlet: 2.9" (74.6mm)
          Length from Mount to End of Drive Spacer: 5.9" (150mm)
          Length from Mount to Crankcase Center: 1.5" (37.5mm)
 

COMMENTS: If using a different brand of oil other than Klotz, OS recommends
            their own mix ratio which may differ from the manufacturers'
            For 40:1, and 50:1 oils, OS recommends a 30:1 gas/oil mixture
          25:1 is 5oz of pre-mixed 2-cycle oil or 151 ml per gallon of fuel
          30:1 is 4.3oz of pre-mixed 2-cycle oil or 126 ml per gallon of fuel
          40:1 is 3.2oz of pre-mix 2-cycle oil or 95 ml per gallon of fuel
          50:1 is 2.6oz of pre-mix 2-cycle oil or 76 mll per gallon of fuel

          The J'TEC Large Wraparound Pitts Muffler will fit this
            engine for inverted mounting applications.
          The Bisson Wraparound and Inverted mufflers will
            also fit.
          The Slimline #2123 and #2123S mufflers will also fit.