What Is the Difference Between Open & Closed Chamber Cylinder Heads?

by Mona Prestenbach
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Open and closed chamber cylinder heads differ in combustion chamber capacity. Although open chamber cylinders offer easier flow, the closed chamber cylinder is better for performance. Compression ratios are also affected by the size of the chambers.

Open Chamber

Open chamber cylinder heads have spark plug areas pushed to meet the edge of the cylinder, creating more room in the chamber. There is less material around the valves in an open chamber, allowing for easier flow. Open chambers have a capacity of 118 cc to 123 cc. Open cylinders have lower compression ratios. Quench areas are smaller and to one side of the head.

Closed Chamber

Closed chamber cylinder heads have higher compression ratios. The increase in compression is due to smaller flow capacity. Closed chambers have between a 100 cc and 112 cc capacity. Quench areas are on both sides of the closed head chamber.


Closed chamber cylinder heads are a good choice for performance vehicle builds. Added combustion in the head produce more power in the engine. Larger valves and hardened seats may be necessary in some engines. Open chamber cylinder heads have smaller quench ares to one side of the head. The smaller quench areas mean fewer emissions. Open chamber cylinder heads are generally used in four-stroke engines and two-stroke diesel engines.

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