If valve timing is incorrect, what effect does it have on cylinder compression?

When valve timing is incorrect, it typically leads to a reduction in cylinder compression. In a gasoline engine, the timing of the intake and exhaust valves is critical for proper engine operation. If the valves open and close at incorrect times, the engine can struggle to achieve the necessary compression ratio within the cylinder.

For example, if the intake valve closes too late, fresh air-fuel mixture may escape from the cylinder before the piston reaches the top dead center (TDC) during the compression stroke. This leads to a lower volume of charge being compressed, thus reducing the overall cylinder compression. Similarly, if the exhaust valve closes too early, it can lead to a situation where residual exhaust gases are still present in the cylinder during the compression stroke, which again diminishes the effective compression since the fresh charge cannot achieve its full potential.

Thus, incorrect valve timing negatively impacts the efficiency of the engine and results in inadequate cylinder pressure, corroborating the answer that it reduces compression. This understanding highlights the importance of precise valve timing for optimal engine performance.