greatly diminished after the 390 and 428 big-block engines became available in the Mustang and Fairlane lines, which offered similar power (at the expense of greater weight) for far less cost. GT-350 The HiPo engine was used in modified form by Carroll Shelby for the 1965–1967 Shelby GT350, raising rated power to at 6,000 rpm and at 4,200 rpm of torque, through use of special exhaust headers, an aluminum intake manifold, and a larger 4-barrel Holley 715 CFM carburetor. The Shelby engine also had a larger oil pan with baffles to reduce oil starvation in hard cornering. Shelby also replaced the internal front press-in oil gallery plugs with a screw-in type plug to reduce chances of failure. From 1966 to 1968, Shelby offered an optional Paxton supercharger for the 289, raising its power (on Shelby GT350s) to around . Production numbers About 25,000 K-code 289's were manufactured at Cleveland Engine Plant 1 (CEP1) between March 1963 and June 1967. 302 4-Bolt Main bearing caps GT-40 Ford designed a new 302 block for the 1967 GT-40, due to a new regulation which limited engine displacement to 5.0 litres. Ford was able to arrive at the 302 displacement by an extra eighth-inch of piston travel to the 289 Hi-Performance V8. The block featured heavy-duty, four-bolt main bearing caps and pressed in freeze plugs. This engine was topped with Gurney-Weslake aluminum heads. About 50 blocks were made. Trans-Am 302 Ford's new 302 "Tunnel-Port" engine was originally envisioned as the secret weapon for the 1968 Trans-Am season, which would bring them a third Championship win. Starting with a 1967 GT-40 block, Ford topped the engine with a new head design. The new heads were based on the design of Ford's NASCAR 427 heads. The intake ports were straight, instead of snaking around the push rods. The push rods actually went through the center of the ports (thus the name "Tunnel-Port"). This configuration also enabled larger valves to be used. The 302 tunnel-port motor was topped off with an aluminum dual quad intake. Shelby dyno sheets showed this engine was capable of producing horsepower in the 440 to 450 range, and operated through a very high rpm band (8000+). Boss 302 The Boss 302 was a chief engineer Bill Gay-inspired and Bill Barr-enacted performance variant of the small block, putting Cleveland-type cylinder heads at their then present stage of development (that's very large valves which