Basically, the stages depended mostly on the carburetion system that was ordered with the engine, with the Stage III being the highest horse power available and it having the Weber 4x2V intake manifold system. The next highest HP engine was the 2x4V (Carter) intake manifold system and the last being the 1x4V (Holley) intake manifold system. All of these were based on varying degrees of preparation except the Weber 4x2V equipped engines which were only available in a full competition form. For example, you could order your 289 Cobra with s 1x4V intake system, a 2x4V intake system installed on a stock 289HP engine or have that 289HP engine race prepared to become a Stage I or a Stage II respectively. The Stage III was only available as a fully prepared racing engine and was only available with a Weber 4x2V intake system. It is also noted in the catalog that depending on the “Stage” of the engine build that there were different camshafts available with a listing for a “roller” camshaft for the Stage III engine, this has been suggested as being false because of the various racing organizations rules governing “roller” camshafts. Also just because a Cobra May have been ordered with a 1x4V or 2x4V intake system doesn’t mean that they were a Stage I or Stage II equipped Cobra, it would have to have been specified as such when the Cobra was ordered new.