At what point does the piston achieve maximum velocity in relation to TDC?

The piston achieves maximum velocity 90 degrees after top dead center (TDC) due to the mechanics of the four-stroke cycle and the geometry of the piston rod and crankshaft. As the piston moves from TDC, it initially accelerates down the cylinder due to the expanding gases from combustion.

At TDC, the piston momentarily comes to a complete stop before changing direction. The velocity then increases as the piston moves downward and reaches its peak speed at the point where it is 90 degrees down from TDC. Beyond this point, the velocity begins to decrease as the piston approaches the bottom dead center (BDC).

Understanding this is crucial because it highlights how the timing of piston movement correlates with the engine's power strokes and the timing of valve operations. This knowledge is essential for optimizing engine performance, as maximum velocity contributes significantly to the efficiency of filling the cylinder with intake air and fuel and providing optimal compression in the next cycle.