Close to the bottom dead center, it finally opens the port to start the admission phase.
Consequently, the piston head approaches the bottom dead center when the port is opened and the admission pressure is achieved.
An excessive admission clearance also causes backflow through the admission port when the piston leaves the bottom dead center.
During the intake of the air-fuel mixture in the Quad-4, a piston moves through a full stroke and past bottom dead center.
Here the exhaust valve remains closed until the piston travels to bottom dead center.