At what speed must a crankshaft turn if each cylinder of a four-stroke cycle engine is to be fired 200 times a minute?

In a four-stroke cycle engine, each cylinder completes one power stroke every two revolutions of the crankshaft. This means that to achieve a firing rate of 200 times per minute for each cylinder, the crankshaft must rotate at a speed that allows each cylinder to complete its cycles accordingly.

Since one firing occurs for each two revolutions of the crankshaft, we can establish that the crankshaft must complete twice as many revolutions as the number of firings per minute to ensure that each cylinder fires at the correct frequency. Thus, if the cylinders are to fire 200 times a minute, the crankshaft must turn at a speed of 200 firings multiplied by 2 revolutions per firing, resulting in 400 revolutions per minute.

Therefore, the correct speed for the crankshaft to turn in order to facilitate a firing rate of 200 times per minute per cylinder in a four-stroke engine is 400 RPM.