Mustang's 289 High Performance Engine - A Hi-Po Happy Birthday
We look back at the Mustang’s 289 High Performance engine option
As expected, it was Carroll Shelby's versions of the Hi-Po which saw the most dramatic successes on the road courses of America and around the world. The exploits of the 289 racing Cobras are legendary, including winning the GT class at the 1964 24 Hours of Le Mans, and the 1965 FIA GT World Championship. On February 14, 1965, Ken Miles debuted the GT 350 in SCCA competition at Green Valley, Texas, and the GT 350 went on to score SCCA B/Production national championships in '65, '66, and '67. Mustang hardtops—both privateer builds and “Shelby Group II notchbacks” were a force to be reckoned with in the early days of Trans-Am. The competition prepped Group II Mustangs contributed the bulk of the victories that led to Ford winning the Trans Am Manufacturers Championship in 1966 and 1967. All started life as K-code Mustang hardtops, before being fitted by Shelby American with most of the tricks applied to GT 350 R-models. According to the SAAC Shelby Registry, 16 were built in '66, and 25 in '67.
GT 350 R-models, such as SFM5R533 seen here, featured well developed Hi-Pos which were balanced and blueprinted, used larger valves, and put out around 350 horsepower. Helping the total performance envelope was the R-model's sub 2,600-pound racing weight.
It's natural to associate drag racing with big-block muscle cars, but the truth is that performance cars of all types have always been welcome on the 1320. Small-block Mustangs have been a bracket racing staple for decades, and seen their share of class racing too. When new, Hi-Po Mustangs typically ran in C/Stock, whereas Hi-Po Fairlanes were often slotted in D/Stock. Extensive modifications might move either into B/FX or C/FX.
289 Cobras ruled A/SP (Sports) with Hi-Po power, with drivers such as Ed Terry, Bruce Larson, Tony Stoer, Don McCain, and Ed Hedrick scoring national level success. On their heels in B/SP or B/Stock were GT 350s, often competing against small-block Corvettes. Some of the more notable B/SP rides were the GT 350s campaigned by Mel Burns Ford and Reynolds Ford.
289 Hi-Po Details
Hi-Po blocks were no different than the garden variety 289s, but were fitted with visibly beefier two-bolt main bearing caps as seen in this side by side example (Hi-Po on the left, standard on the right). Later Mexican 302s featured main caps which were very similar to the Hi-Po caps
These comparison photos show the clear difference between a passenger side Hi-Po exhaust manifold (top), and a standard 289 manifold (bottom). While far from an equal length header, the longer and more streamlined Hi-Po manifolds were clearly superior.
Plenty of easily missed engineering features contributed to the overall success of the Hi-Po 289, both in terms of performance and reliability. Among these features were larger generator or alternator pulleys. The larger pulley spun the generator/alternator slower for a given engine RPM, thus keeping speeds tolerable during predictable Hi-Po high-rev antics.
Likewise the cooling fan on a Hi-Po differed from other Mustang fans. Above is the K-code specific five-piece fan which featured aluminum blades for lighter mass and improved cooling. Above that is the non-AC two-piece steel fan used on C-code and A-code Mustang 289s.
Hi-Pos were the only small-block Windsor to feature a purely mechanical advance distributor (no vacuum), and they were dual-point as well for improved high-rpm ignition.
Hi-Po 289s didn't feature a bigger valve size than their same year low performance brethren, but that's not to say they weren't special. Arguably the biggest difference was the cast in spring cups where the valvespring contacts the head. The spring cups (above top) were another attempt to provide high-rpm valvetrain stability, and are only present on Hi-Po heads. Certain service replacement castings had a HP logo cast in the area visible under the valve cover, but production heads never did. Hi-Po heads also used stiffer valve springs with an inner dampener, and always used early style standard rocker arms/guide slots in the head, as opposed to the “rail” rocker arm arrangement (above bottom) that debuted on other 289 heads for 1966.
Another feature found only on Hi-Po heads were screw-in rocker studs as opposed to press-in studs. Whether the screw-ins were absolutely necessary for the modest valve spring pressures of factory Hi-Po springs, or not, they certainly were critical when stiffer aftermarket springs and bigger cams were installed by owners at a later date. In this picture, an original Hi-Po stud is shown on the left, a later Ford replacement on the right.
Hi-Pos featured slightly larger and uniquely calibrated Autolite 4100 four-barrels as compared to A-code 4100s. As well, when the Autolite 4300 debuted in 1967 on A-code 225-horse 289s, Hi-Pos continued to use the 4100. While a Ford source denoting Autolite carb cfm hasn't been found, several experts believe the K-code carb to be around 600 cfm, and the A-code around 480 cfm.
Various Hi-Po 289 racing accolades
• 24 hours of Le Mans GT Champion, 1964-Cobra
• FIA GT World Champion, 1965-Cobra
• SCCA B/Production Champion, 1965-67-GT 350
• SCCA Trans Am Champion, 1966-67-Mustang
• SCCA A-Sedan National Champion
• Shelby Group II Mustangs were highest finishing American sedans at the 24 hours of Daytona, 1966, 1967