When a valve has a 30-degree face, what should the seat angle be?

When a valve has a 30-degree face, the recommended seat angle should typically be slightly greater than the valve face angle to ensure a proper sealing surface. This design choice helps to create an optimal contact area between the valve and the seat, improving the engine's efficiency and preventing leakage.

In the case of a 30-degree valve face, a 31-degree seat angle allows for an optimal fit. The slightly steeper angle of the seat compared to the valve's face facilitates better seating dynamics, enabling the valve to close securely and maintain compression within the combustion chamber.

Choosing a seat angle that exceeds the valve face angle by a small margin is standard practice in engine design. It promotes effective sealing while minimizing the risk of premature wear or failure at the sealing surfaces. The seat must be machined precisely to achieve this relationship, ensuring that when the valve closes, it seats properly to avoid any gaps that could lead to leakage or loss of performance.