Basic Engine and Propeller Performance
Introduction
The purpose of this page is to discuss performance-increasing modifications to the engine and propeller system of the Grummans. Because performance can mean different things, actual increases in performance are discussed in the appropriate Performance sections.
The Lycoming O320
The O320 on Grummans is a horizontally-opposed, carbureted, 4-cylinder engine with 320 cubic inches of displacement. This engine typically comes in low compression (7:1) and high compression (8.5:1) varieties. The low compression version was rated by Lycoming at 150HP at 2700RPM, and the high compression engine was rated at 160HP at 2700RPM. The Cheetahs came from the factory with the low compression engine. Bill Scott of Precision Engine developed an STC to convert the low compression cylinders to high compression cylinders with an RPM restriction of 2650RPM. The RPM restriction allowed Bill Scott to avoid testing since the restriction placed the high compression engine within the tolerances allowed by the FAA for the low compression engine. The FAA will no longer approve changes of this type without testing. The maximum horsepower, with the RPM restriction, is roughly 157 HP.
