The X code is a 390 cid engine. Used in the full size Fords, Mecurys and Lincolns in the 60s and some trucks. It was a 2 barrel carb and had good torque. The 4 barrel version (S code) had a 4 barrel carb and made 40 more ft/lbs of torque in stock form. The real stomper of the '60s was the 427 cid engine (W code) side oiler (also available as a top oiler) and was actually 425.98 cid. But Ford called it a 427 to differentiate it from the rivaled Chrysler 426 Hemi. Chevy didn't have a qualm with their the big inch GM engines and also had a 427 and was fuel injected in the Corvette. The Ford 427 side oiler was probably the best of the lot as the later FE 427s were essentially factory racing engines. Introduced in 1958, horse power/torque varied, as it was meant for buses, trucks. However, the ruggedness of the engine and big displacement made it attractive for NASCAR racing. Few were produced in the full size cars and only to qualify for NASCAR acceptance at the time with the first passenger cars equipped with them in '63. However Shelby put them in the Cobra in about '67 or '68. Ford advertised the engine was 390 hp with 460 ft/lbs of torque. In real life the engine put out upwards of 500 hp! Today the side oilers are rare collector items. Shelby initially put the K code engine in the Cobra. With excellent horsepower to weight, it won Le Mans in '66.
