The History of the K Code engine
In 1963 Ford released the first 289 High Performance engine which produced 271 BHP @ 6000 RPM. It was first introduced into the Fairlane and then the Comet and finally ended its run in the Mustang. The 289 "HIPO" engine also made its way into the first Shelby AC Cobras and the Shelby GT350 Mustangs through 1967.
It was given the letter assignment K in the first Fairlanes and Mustangs
cars. Some of the key aspects of this engine were the stronger connecting rods with 3/8" bolts, thicker main bearing
caps, solid lifter cam, screw-in rocker arm studs, machined valve spring seats,
a 600 CFM Autolite carburetor, dual point mechanical advance distributor, and
better flowing exhaust manifolds.
The 289 HP featured a high nodularity cast iron crankshaft that was Brinell hardness tested to ensure quality. Some believe the crank was just a regular crank that was pull off the line and tested. To prevent harmonic vibrations from destroying the crankshaft at higher RPM, the engine used a different vibration damper and an add-on counterweight. A portion of the 28.2 oz. in. imbalance found in the normal small block damper was moved to the additional counterweight. Moving the mass in towards the front main bearing reduced bending loads on the crankshaft. The special damper also had a larger more massive inertial ring. The add-on counterweight was 0.150" thick. As a result a special crank sprocket was used, C3OZ-6306-A, itself being 0.150" thinner than the normal 289 sprocket. The counterweight was both keyed to the crankshaft and indexed to the sprocket with a 1/8" roll pin.
For the Mustang The famous "K-code" became high-compression, solid-lifter, four-barrel 289 pumping out a lusty 271 horsepower. K-code-equipped cars got a special badge on their front fenders indicating that not only did the engine displace 289 cubic inches, but that it was also the "High Performance" version. Serious drivers opted for the K Code. It was the same race proven HIPO motor found under the hood of Shelby's GT 350. Not only was the motor upgraded but the key suspension parts were also upgraded as well as the clutch, transmission, drive shaft and rear differential in essence the entire driveline of the car was performance orientated. Ford only offered a four month warranty on the High Performance motor as compared with a 2 year warranty other all other cars. They must have guessed it was going to be raced a lot.
HIPO Engine facts
The ultimate book on early small block Ford engine including the HIPO