This is a video I made on the Rarest Ford Head in my opinion, created by Darin Morgan. To me they are rare, as I doubt there are many sets like this. We know Bob Glidden, was making this combustion chamber, on his Ford 351Cleveland iron heads, back in 1975. I discovered this by chance, looking through old photos that the Peterson museum had taken. I had made a video, documenting this. Bob Glidden's Pro stock 351 Cleveland Heads, his secret revealed. Talking with Rusty Glidden confirmed this. I will put a link so you can see the whole video. These heads started out as a set of A3 Ford Motorsport Aluminum heads. The A3 was the first Ford Motorsport Aluminum head. These came out in the early 80s, and were followed with multiple versions, including, the A4, ultra rare, B3, C3....and then the C3 Yates, which lead to the D3. It was basically an aluminum version of the Ford 351Cleveland iron 4V head. The iron Cleveland 4V head, was used as the basis for the High Port Pro Stock Cleveland heads that Bob Glidden, Dyno Don Nicholson, Gapp&Roush, and many others used in the pro stock wars of 1975-1981. Prior to and after those years, Big Blocks were raced. The floor of the stock intake port is raised, the same as if you filled it with port stuffers. Inserts, either aluminum, or epoxy, placed on the floor of the intake runner where it meets the intake port, to straighten and increase velocity. The exhaust port is raised the same as the old Iron Pro stock heads, with the iron exhaust port cut off, and a raised 1.25 inches aluminum plate bolted on, and ported to match the transition. This allowed for straighter exit, and increased flow. They the port plates added roughly 25hp. These secret A3 heads have the benefits of the Iron high port configuration, but in aluminum. These heads have had extensive porting, but what is really unique, is the cortoid shape of the combustion chamber. This encompassed a huge amount of welding rod, and effort. Thank you Darin Morgan. These are going to be used for the ALCOA Supra Cast Aluminum TrackBoss 427 Cleveland...Stay tuned. Happy 6 th Birthday Alaina.