Where are the exhaust holes of the two cylinders?

The lower part of the cylinder wall. The cylinder works according to the pressure difference between the front and rear of the piston, so it is necessary to connect the front and rear pipe joints, so the exhaust holes of the two cylinders are placed at the lower part of the cylinder wall. Cylinder is a cylindrical cavity in an engine, in which there is a piston driven by the pressure or expansion force of working fluid, and there are similar but non-cylindrical parts in some special engines.