The 300D is an air-cooled, 6-cylinder, 4-stroke, horizontally opposed engine. This means the engine has a central crankcase, with three cylinders on each side. Many engines use this horizontally opposed configuration because it's an efficient design. The propeller mounts directly to the crankshaft. The carburetor is slung below the engine. This is unique, because most engines have the carburetor above the engine. On the back of the engine are the starter, the alternator and the magneto. The magneto produces the high voltage needed to fire the spark plugs.
The displacement is 301 cubic inches.The engine's bore is 4.06 inches. Bore refers to the diameter of the piston. The stroke is 3.88 inches. Stroke refers to how far the piston travels back and forth in the cylinder. The engine produces 145 horsepower at 2,700 rpm. Because this is an aircraft engine, it is not designed for a wide rpm range, like a car engine. According to Continental, this engine is designed for continuous operation at 2,700 rpm, which is also the maximum recommended rpm.
The overall engine length is 36 inches, the overall width is 31.5 inches and the height is 27.41 inches. The dry weight is 248.70 lbs. The overall weight, with accessories such as the starter attached, is 300 lbs. Dividing 145 horsepower by 300 lbs. yields roughly one-half horsepower per pound power ratio.
The 300D requires is a minimum of 80- to 87-octane aviation gasoline. The oil capacity is 8 quarts. For temperatures below 40 degrees F, oil weight of 10W-30 to 20W-50 is acceptable. For ambient temperatures above 40 degrees, 15W-50 to 20W-60 is acceptable. The oil must be at least 75 degrees F at takeoff. Letting the engine warm up before takeoff usually accomplishes this. As a matter of safety, the pilot has to check his oil temperature gauge before takeoff.