Eric English
June 2, 2014
Photos By: Source Interlink Media Archives, Bob Mannel

Somewhere on the heels of celebrating the Mustang's 50th birthday, we find it appropriate to commemorate that same half century mark for the iconic pony's very first high performance engine—the 289 High Performance. Of course most of us lovingly refer to it as the Hi-Po 289, and it played a huge role in putting Mustang on the roadmap for real car lovers across the land. Available within a couple of months of the April 17th Mustang debut, and lasting through 1967, it was this engine which made Mustang more than just a pretty face; more than a sporty looking secretary's car. Simply put, the Hi-Po 289 literally transformed Mustang into a true performance machine.

Before we go any further, let's be quick to acknowledge the 289 High Performance's debut in the Fairlane during the 1963 model year. From that perspective, the Hi-Po has already crested the half century mark. Since our focus here is Mustang-centric, perhaps we'd be better off framing our celebration story as a “Happy Birthday Hi-Po Mustang”. From this perspective, we remind readers that all Hi-Po Mustangs carry a K as the fifth digit in the VIN, thus the “K-code” description often seen.

Nineteen sixty seven was the last year for the K-code Mustang, and with in-house competition from the newly available 390 big-block GT, very few were produced. Kevin Marti’s data shows that just 489 were built, and unlike in earlier years, the GT (or GTA) package was required. This is Gary McKay’s incredible K-GTA convertible—one of just 50 droptop Ks built for 1967—16 of which were GTAs.

The Hi-Po strutted its 271 horsepower stuff with heavy duty engine components, mandatory four-speed transmission (until 1966), and a tough as nails 9-inch rear. The beefier engine components were present top to bottom, what with a solid lifter cam and associated valvetrain, larger two-bolt main caps, better connecting rods, and a high nodularity iron crankshaft. Add in a dual point distributor, Hi-Po specific exhaust manifolds, and a host of smaller supporting cast members, and you had a balanced package all the way around.

The automotive press of the day was impressed—although multiple magazine drag tests in the mid-high 15s aren't much to write home about today. Arguably the downfall of the Hi-Po was too few cubes, a low-rise induction package shared with the A-code 225-horse engine, and the same small valve sizes common to all sixties-era Mustang 289 and 302 small-blocks. Yet helping make the whole thing work well was the lightweight nature of the new Mustang, owing to its economical Falcon roots. You simply don't need huge power to smartly move 3,000 pounds, and that lithe weight also does wonders for cornering and braking. Carroll Shelby capitalized on all this with his GT 350, born from K-code chassis' and bolstered with some of the goodies Ford left on the table. Namely we're speaking of the hi-rise aluminum intake, Holley 715-cfm carb, Tri-Y headers and voila, you've gone from an advertised 271 horsepower right up to 306. Better than 1 horsepower per cubic inch was still pretty heady stuff in 1965.

Race versions of the Cobra and GT 350 were often around 350 hp with a single four-barrel—take for instance a GT 350 R-model engine. Such Hi-Pos did get improvements in the cylinder head department, what with larger valves (1.875/1.60-inch) and porting, more camshaft, bigger headers, etc. Dual quad or Weber induction, when allowed, made for even more power. In the end though, it's the street versions of the Hi-Po Mustang which have made it the legend that it is. Sure, there were plenty of faster cars in a straight line, more solid and luxurious muscle cars, and cars with a more pure and distinct sports car persona. And yet none of them ever sold like a Mustang, and none had the broad popular following. Mustang hit all the buttons for a vast base of people, with a pretty face, economical price, and a fun to drive demeanor led by none other than the K-code 289. So Happy Birthday Hi-Po Mustang—and a toast to another fifty!

This is a “factory correct” engine compartment, but sharp eyes will no doubt wonder how that can be. Whether in a Fairlane or Mustang, Hi-Po 289s weren’t available from the factory with air conditioning, right? True, but one could argue that there were four legit exceptions, including the one here. This is the engine compartment of Len and Linda Perham’s ’66 GT 350 convertible. That’s right; the four very special and unique ’66 GT 350 convertibles were all fitted with A/C at Shelby American.

Hi-Po Values

We hate to broach the subject of Mustang values in general, because there are so many variables. K-code Mustangs are no different, with wildly varying advertised and selling prices. Just one example can be seen in the results of the 2014 Barrett Jackson auction at Scottsdale. Mining the sold results from the auction on the Barrett-Jackson website (www.barrett-jackson.com), we found lot number 1565, a K-code/four-speed '66 Mustang GT convertible; Candyapple Red over black pony interior (original colors) which sold for $49,500. Likewise the same auction sold lot number 966 for $84,700, which seemed a virtual twin in terms of option—body style, colors, drivetrain, etc. save for a claimed 125K fresh restoration. Having never laid eyes on either, it's hard to opine, but one was clearly nearly twice the money.

We perused NADA and Hagerty classic car value websites, and found interesting numbers, along with some head-scratching discrepancies. For example it's possible on the NADA site to equip a '65 Mustang with a 390, and to arrive at an estimated value for such. On top of offering a combination that never existed, the ever-popular 200 hp 289 option is noticeably absent. With Hagerty it seemed the value calculator didn't understand that a base '65 or '66 Mustang could be optioned with a 271hp 289, limiting the option to a Mustang GT. Yet regardless of the omissions/errors of either, we offer the following examples of pricing from both sources:

NADA, 1965 Mustang (non-GT) (High Retail) 225hp 289 271hp 289
Hardtop 36,750 $41,160
Convertible 57,500 $64,400
Fastback $57,250 $64,120
NADA, 1965 Mustang (non-GT) (High Retail) 225hp 289 271hp 289
Hardtop 36,750 $41,160
Convertible 57,500 $64,400
Fastback $57,250 $64,120

Production Data

We've explained in the past how Kevin Marti's exhaustive Ford database begins with the 1967 model year, and when it comes to '67 Mustang K-code cars, the records show just 489 were built. Unfortunately in the absence of data for the '64½-'66 model years, production numbers are vague at best. Some hard numbers float around in certain books and internet sources, but an explanation for the data source is always missing, and we discount those numbers because of it.

To get some idea of how many '64 ½-'66 Hi-Po Mustangs might have been made, we turned to Bob Mannel, who literally wrote the book on all things 289. His monstrous “Mustang and Ford Small Block V8, 1962-1969” from RPM Press, is a minutia laden tome that is a worthy addition for any sixties-era Ford fan (www.fordsmallblock.com). Bob also runs the Hi-Po Fairlane Registry, and so we figured if anyone had some good ideas about how many K-code Mustangs were built, Bob would be a good bet. All of that said, Mannel is quick to emphasize his guesstimates are based on educated extrapolations of data, and should certainly not be viewed as hard and fast. Nevertheless, his insight gives us something to consider. Not including GT 350s, Bob believes around 600-800 K-code Mustangs were built for '64½, 3,500 for '65, and 2,500 for '66. This is based on familiarity with how many Hi-Po engines were manufactured, how many Hi-Po engines Ford generally produced each month, how many went into Fairlanes and Cobras, and other factors. Bob would love for conclusive numbers to be discovered some day, but until that time…

Seen here are two of the very worthwhile upgrades which Shelby American applied to the Hi-Po 289 for GT 350 production. Holley’s 715-cfm carb atop a Cobra lettered aluminum hi-rise intake. The Holley used vacuum secondaries and Le Mans style bowls.

Road Racing

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.

Drag Racing

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.

Brant Halterman’s ’64½ K-code convertible is a true beauty, and one of many Hi-Pos over the years to get a kick in the pants via a Ford over-the-counter induction system. This one is the “Three 2V Induction Kit,” which was advertised in Ford’s 1966 High Performance parts catalog to boost power by 12-15 horsepower over a standard four-barrel. The setup retailed for $219.50, while the open letter Cobra valve covers in the same catalog rang the till at $46.70.

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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.

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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.

A row of K-code Mustang fastbacks undergo conversion to GT 350 status at Shelby American in 1965.

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
1967-John McComb
• Shelby Group II Mustangs were highest finishing American sedans at the 24 hours of Daytona, 1966, 1967