vertical and horizontal engine.

A general purpose horizontal motor is typically built with external shaft loading in either or both the radial or axial direction. ... Vertical motors, on the other hand, are expected to handle the axial or radial thrust associated with the pump they are driving.
Horizontal engines have the lower centre of gravity than the vertical one. It gives a smoother ride and reduced vibration. The most horizontal engine frames are designed like that way which provides more space and stiffness.

The horizontal engines are better aligned with the air flow direction and hence get cooled easily. The most of the parts of the horizontal engines are exposed to the air this adds up to the cooling by air .