Which type of engine typically does not allow rings to rotate around the groove of the piston?

In high compression ratio engines, the design often incorporates stationary piston rings that do not rotate around the groove of the piston. This design choice helps to enhance the sealing efficiency between the piston and the cylinder wall, which is crucial for maintaining high compression and improving power output. By preventing ring rotation, these engines reduce the chances of unwanted oil passing into the combustion chamber, thereby minimizing oil consumption and emissions.

In contrast, many standard four-cycle engines are designed to allow some degree of rotation of the piston rings. This rotation can help to promote more even wear and provides better lubrication over time. High performance and low compression ratio engines also typically will have some allowance for ring movement, as the dynamics of those engines can benefit from it. Therefore, the stationary design of the rings in high compression ratio engines sets them apart from other types.