What directly affects the contour of cam lobes in an engine?

The design of valve operation directly affects the contour of cam lobes in an engine because the cam lobes are specifically shaped to control the timing and movement of the engine's valves. The cam lobe's profile determines how the valves open and close, influencing the engine's performance, efficiency, and power output. Each cam lobe's contour must be precisely designed to ensure that the valves operate at the right time and to the right extent, allowing for optimal air and fuel mixture flow into the combustion chamber and exhaust flow out of it.

The other aspects mentioned, such as the size of the crankshaft, the configuration of the engine, and the length of the intake manifold, do not impact the shape and design of the cam lobes directly. While they can affect engine performance in different ways, it is the cam lobe design that specifically determines the operation of the valves.