IOE engine

The intake/inlet over exhaust (IOE) engine, also known as F-head (in the USA) and pocket valve, is a valvetrain configuration used in early four-stroke internal combustion engines. The configuration consists of inlet valves located in the cylinder head and exhaust valves located in the cylinder or engine block.

IOE engines were widely used in early motorcycles, initially with the inlet valve being operated by engine suction instead of a cam-activated valvetrain. When the suction-operated inlet valves reached their limits as engine speeds increased, the manufacturers modified the designs by adding a mechanical valvetrain for the inlet valve. A few automobile manufacturers, including Willys and Rolls-Royce, also made IOE engines for their cars. Rover manufactured a line of engines with a particularly efficient version of the IOE induction system.

A few designs with the reverse system, exhaust over inlet, or EOI, have been manufactured.

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