In a piston engine, the moving pistons are usually designed to be flush with the top of the cylinder block and at a top dead centre position. The combustion chamber is sunken into the cylinder head and commonly contains a single intake valve and a single exhaust valve. Various shapes of combustion chamber have been used, such as L-head (or flathead) for side-valve engines, “bathtub”, “hemispherical” and “wedge” for overhead valve engines and “pent-roof” for engines having 3, 4 or 5 valves per cylinder.

The shape of the chamber has a noticeable effect on power output, efficiency and harmful emissions, and so the designer’s objectives are to burn all of the mixture as completely as possible while avoiding excessive temperatures.

A pentroof head is a cylinder head in which each combustion chamber has its spark plug located close to the centre of the combustion chamber. When the spark plug is located in a central position, the flame spreads a minimum distance in all directions allowing for a balanced and clean ignition of the fuel-mix inside the combustion chamber. We hope that helps answer the question ‘What is What is a Pentroof Head?’!

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