Rotary Engine Porting

Quick Intake Port Type Summary

Similar to how cams of various profiles are available to achieve desired goals, there are many varieties of rotary port shapes that have been developed for different purposes. Some shapes simply extend the closing timing for turbo applications, while others create massive amounts of overlap and maximize port volume for ultimate peak horsepower on a non-turbo race engine.

Unfortunately, again, there is no universal naming scheme, but I will do my best to categorize them and explain their purpose. First, any port that keeps within the ordinary physical boundaries is essentially a variety of street port. Within these boundaries, a number of shapes is possible and several naming conventions have been used to describe them. In non-turbo applications, there are usually three basic sizes/shapes of port: street, tear, and rally, going from smallest to largest.

A street port is a very minimal enlargement that does not affect idle quality. A tear port is a bit bigger, with more overlap, and fully supports the rotor's corner seal. And a Rally port is typically a maximum effort, advancing the leading edge to the point it only supports slightly more than half of the rotor's corner seal and extends the duration as far as is practical for ultimate high end power. Some people simply call these small, mild (or medium) and large street ports.

In turbo applications, increased overlap is generally avoided so that opening timing is not advanced. Instead, the duration is increased by extending the trailing edge to the desired degree. A moderate increase in duration is usually called a mild port' and a more extreme case is sometimes called an 'extend port'.