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There are various types of cylinder head in motorsports and here we focus on hemi-head and wedge-head cylinders only.
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| Summit Racing |
It may be difficult to answer if the hemi cylinder head (hemispherical chamber) must produce better horsepower for all engines because there are numerous variants in Motorsports. In the Chevy 302 engine, we observe that the hemi cylinder head allows the engine to run quicker. The hemi-head draws benefits from superior valve placement and minimize the effect of valve shrouding. The hemi-head is easier to fit larger valves into any given bore radius. As a result, the effectiveness of cylinder-filling, crossflow dynamics, volumetric efficiency and engine output are improved. With a hemispherical chamber with splayed valve stem angle, the total valve diameter size may exceed the bore size under curvature. The splayed valve angle tilts the valve seat plane which allows a straighter flow path for the intake and exhaust process. However, the hemispherical chamber is more expensive and the mass is heavier.
The wedge-head offers a simplified valve actuation by putting the valves side by side within the chamber. But the main drawback is that it restricts the flow of the intake and exhaust into and out of the chamber and also difficult to put 4 valves into one cylinder.
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| autowise |
While the hemi-head gives a better airflow management, the advantage of using hemi-head is more pronounced at high rpm region as shown in the following figure.
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| Measurement data: *The intake & exhaust valve diameters of the stock hemi-head and wedge-head are the same |