What happens to performance if the intake valve closes on the compression stroke?

When the intake valve closes during the compression stroke, it has a significant effect on the engine's performance, specifically on the compression efficiency. Closing the intake valve at the right point allows for the maximum compression of the air-fuel mixture in the combustion chamber. This maximum compression contributes to better thermal efficiency and more complete combustion, which ultimately increases the power output of the engine.

By maximizing compression efficiency, the engine can produce more power and run more effectively during combustion, as a greater volume of the air-fuel mixture is subjected to higher pressures and temperatures. This leads to a more powerful explosion when ignited, enhancing overall performance.

In contrast, if the intake valve remains open too long into the compression stroke, or closes too late, a portion of the air-fuel mixture can escape back into the intake system. This not only reduces the amount available for combustion but can also lead to inefficiencies and less effective engine operation. Therefore, closing the intake valve at the correct moment is crucial for achieving optimal performance in reciprocating engines.