Question

The standard practice for sizing the exhaust valve is to make them a certain percentage ____________ than the inlet valves.

(a) larger

(b) smaller

(c) unpredictable

(d) none of the mentioned

The question was posed to me in unit test.

This is a very interesting question from Total Engine Friction in chapter Engine Friction and Lubrication of IC Engine

Answer 1

The correct answer is:

(b) smaller

The standard practice for sizing exhaust valves is to make them a certain percentage smaller than the inlet valves. This is because the exhaust gases have already been expanded and are at a lower temperature and pressure compared to the intake charge, so less flow area is required for the exhaust valve compared to the intake valve. Additionally, exhaust gases are often less dense, further reducing the need for a large exhaust valve.