Ford Mustang FAQs

A high-performance version of the 289 engine was introduced late in the 1963 model year as a special order for Ford Fairlanes and Mercury Comets. The engine is informally known as the “HiPo” or the K-code. Starting in June 1964, it became an option for the Mustang.

The HiPo engine was engineered to increase performance and high-RPM reliability over standard 289 fare. It had solid lifters with hotter cam timing; 10.5:1 compression; a dual point, centrifugal advance distributor; smaller combustion chamber heads with cast spring cups and screw-in studs; low restriction exhaust manifolds; and a bigger, manual choke 595 ft³/min carburetor. The water pump, fuel pump, and alternator/generator pulley were altered; fewer vanes, extra spring, and larger diameter respectively; to help handle the higher RPMs. Even the HiPo’s fan was unique. Bottom end improvements included thicker main bearing caps and balancer, larger diameter rod bolts, and a hardness tested and counterweighted crankshaft, all for high-rpm reliability. The HiPo carried SAE gross ratings of 271 hp at 6000 rpm and 312 lbf·ft at 3400 rpm.

The HiPo engine was used in modified form by Carroll Shelby for the 1965-1967 Shelby GT350, raising rated power to 306 hp at 6000 rpm through use of special exhaust headers, an aluminum intake manifold, and a larger carburetor. The Shelby engine also had a larger oil pan with baffles to reduce oil starvation in hard cornering. Shelby also replaced the front press-in oil gallery plugs with screw-in plugs to reduce failure.

From 1966 to 1968, Shelby offered an optional Paxton supercharger for the 289, raising its power on Shelby GT350s to around 390 bhp. One was sold. The K-code HiPo engine was an expensive option and its popularity was 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.