This document provides an overview of six-stroke engine designs that aim to improve efficiency over traditional four-stroke engines. It describes the working principles of various six-stroke engine types, including single piston designs by Griffin, Bajulaz, Crower, and Velozeta as well as opposed piston designs like the Beare head engine. The document also discusses the modifications needed to convert a conventional engine to a six-stroke design and analyzes the advantages of six-stroke engines like reduced fuel consumption and emissions.