Mustang Member Story: The K-Code Transformation of a ’65 GT

April 17 marked 60 years since the Ford Mustang’s public debut at the 1964 New York World’s Fair. The original pony car immediately became a pop-culture and automotive phenom, and it remains one of the most impactful cars in history. We’re celebrating with stories of the events surrounding the Mustang’s launch, the history of the early cars, and tales from owners. Click here to follow along with our multi-week 60 Years of Mustang coverage. -Ed.

When the 289 in my 1965 GT Mustang was ready for a rebuild after 15 years of driving, I made a decision not unfamiliar to owners of original Mustangs: If I was going to pull the car’s motor and have it overhauled, why not take the next step and upgrade the driving experience? Rather than opting for a stroker kit, a roller cam, or some other modern engine upgrade, however, I decided to do something a bit more historic: a period-correct conversion of my car’s original 225-hp A-code into a replica of the high-performance, solid-lifter K-code 289. In fact, while my mechanic and I were at it, why not push the replica idea to the next step and give the car a “Cobra 289,” the 306-hp version of the engine Carroll Shelby tweaked for the GT350?

Now, this kind of transformation has been an enthusiast option that goes all the way back to 1965. It’s been the subject plenty of magazine and online articles and videos, and you can buy replica K-code 289s on eBay.

The coupe was far and away the most common body style of those original Mustangs. Ford moved more than a million coupes in the first generation but barely 100,000 fastbacks, and two-thirds of those sold in 1965. After the first year’s novelty, fastback sales plunged drastically.

For those of us who were on the scene then, none of this is a mystery. The coupes were minimally less expensive than the fastback or convertible, but that wasn’t the reason 80 percent of all 1965–66 Mustangs were coupes. Rather, the ’60s generation simply preferred the original, the version Lee Iacocca sprang on the world in the spring of 1964, the car that won the Tiffany Award for Excellence in Design. At a time when many Mustang buyers owned only one car, coupes offered a slight advantage in rear seat headroom and trunk space over fastbacks. They even possessed a slight performance edge as they were the lightest of the three body styles. As dazzling as the sleek fastbacks seem now, as fetching as convertibles are in the market, in the 1960s, it was easy to be smitten with the Mustang coupe. Only after about 1968 did the fastback Mustang begin to replace the coupe in our collective affections.

In high school and college I owned three Mustangs—a pair of Springtime Yellow ’66 coupes and a Candy Apple Red ’68 fastback. But none of those cars approached the special qualities of the car I bought in 2004 to salve my Mustang nostalgia. What I had always swooned over was an original GT, the first performance/cosmetic version of the Mustang. Offered only with the two top engines, Mustang GTs got disc brakes, quicker steering, and stiffer suspensions, along with eye candy like round gauges with 140-mph speedometers, fog lights, trumpet exhausts through the rear body, and racing stripes.

The GT cars were beautiful regardless of body style, but another original Mustang truth is that the majority of factory GT cars were coupes. Most weren’t strippers, though. As period road tests (like the one Motor Trend did of a ’66 GT) and books on Mustang history offer as evidence, a common look for the original GT Mustang was a coupe with a two-tone body, with rocker panel racing stripes matched to a black or cream vinyl top designed to set off a complementary paint color. It was a striking aesthetic combination then, and still is now.

This was the Mustang that had always entranced me. What I found and bought in 2004 was one of the first run of Mustang GTs built. It came out of the San Jose plant in May 1965, the second full month of GT production, as a two-toned coupe with white stripes and cream vinyl top gracing a Silver Blue body. Driven off the truck onto the Al Cheney Ford lot in Santa Cruz, California, the car was absolutely loaded. Beyond the GT package and A-code 289, its options included Cruise-O-Matic, air conditioning, power steering, Rally-Pac gauges, styled-steel wheels, dual red-band tires, an Equalock differential, deluxe two-tone interior, deluxe steering wheel, deluxe seat belts, a console, radio, a vinyl top, banded tinted glass, the convenience group, backup lights, an interior-controlled side mirror, a passenger side mirror, and two-speed wipers. Despite lacking the ultimate option—the Hi-Po engine—with delivery and dealer prep, this car was a $4000 showroom starlet, rare altitude for a factory Mustang.

Then there was its subsequent history. As a loaded GT, it had clearly impressed its early owners enough that when it came to me 40 years down the line, not only were its factory engine and transmission still in place, it still sported all its date-coded tinted glass. Equally indicative of a rare, no-hit lifetime, fore and aft it wore its first set of dealer license plate frames from that initial Santa Cruz sale at Al Cheney Ford. Fingering the patina on its worn ignition key, a friend offered that when that key was bright and new this car would have been cruising California’s Highway 1 with the Beatles’ latest, Rubber Soul, playing on its radio.

The car came to me with a ten-year-old, mostly cosmetic restoration familiar to anyone who watches auto-garage TV. The engine had gotten a rebuild, and the car had been resprayed in its original color and given a new interior. Aesthetically, it was gorgeous. Beneath the skin, as a mechanic who looked at it for me said, it was “bone stock.” I proceeded to replace the woodgrain appliques on the dash with real wood and attended to various faults as they surfaced. But in its new home at the foot of the Rockies in Santa Fe, New Mexico, for its next 20,000 miles I mostly just drove it. Eventually, a tired and protesting suspension, grabbing brakes, faltering compression, and oil smoke on start-up signaled the time for a full mechanical restoration.

In good tune, a 289 Mustang is a lovely road-trip or daily-driver car. Few of us really use collector cars that way, though. I mostly drive my classics on local roads to enjoy their acceleration, their throttle response, and the analog way they react to driver inputs. An A-code 289 is still torquey enough to run light-to-light with modern city traffic, but no one would call it scintillating on an empty road. No one did in the day, for that matter. Motor Trend’s road test of a ’66 GT yielded a 0–60 time of 9.5 seconds and the quarter-mile in 17 seconds, at 81 mph. Riding in the Silver Blue coupe the first time, my wife’s reaction was, “So this is mainly a car that sounds nice, huh?”

So, with a loaded and very sound ’65 GT in need of a mechanical restoration, the time was at hand for whatever upgrades I envisioned for it. Why not impart, then, the kind of performance those GT cosmetics and red-band tires had always implied? Why not give this GT that one option it didn’t get in 1965?

A historical upgrade seemed proper, anyway. This was a car so straight out of the ’60s it begged for a period hop-up. I turned the restoration over to Steve Chiulli of Green Monkey Coachworks in Santa Fe. Operating from my obsessively researched build plans, Chiulli launched a mechanical restoration that took nearly eight months. Saving the replica Cobra 289 engine for the moment, here’s what we created.

An entirely new suspension was part of the work, so we started by mimicking one of the handling tricks Shelby’s shakedown driver, Ken Miles, developed for the GT350: dropping the pivot point for the control arms one inch to keep the wheels upright in fast cornering. This gave the finished car the raked stance of the 1965 GT350. We used another Shelby/Miles trick to get additional stiffness, adding the more robust “export brace” and a “Monte Carlo bar” to the engine bay. As with GT350s, red Koni shocks became a part of the rebuilt suspension. We then traded out the leisurely 3.00:1 A-code final gearing for a much shorter 3.80:1 ring-and-pinion limited-slip differential. With the A-code’s 8-inch differential, that was the closest match to the 3.89:1 Shelby utilized in the 8.75-inch diff of the GT350. Finally, following Ford’s lead when it mated the K-code with Cruise-O-Matic, we gave the transmission a general uprating along with a shift kit.

Converting my A-code 289 into a replica Hi-Po, then Shelbyizing it to GT350 specs, was the heart of this rebuild. And critical to the beating heart of the Ford high-performance 289 was its solid-lifter camshaft. We sourced one for my engine from Comp Cams, whose Nostalgia Plus K-Kit promised a “tight lash with the distinctive sound and character of Ford’s 271-hp 289.” Installing this re-creation Hi-Po cam in my rebuilt 289 block involved machining the A-code heads to accommodate a K-code valvetrain, including recessing the spring seats for the stronger valve springs and machining for screw-in rocker arms. New flat-topped pistons provided the K-code’s high compression. That done, we replaced the cast A-code intake with an aluminum hi-riser, then changed out the 480-cfm Autolite four-barrel for a remanufactured 600-cfm Autolite. Shelby used a 715-cfm Holley on manual GT350s, but his automatic cars retained the 600, so we did, too.

On the exhaust end, Tri-Y headers replaced the A-code manifolds, then fed through MagnaFlow glasspack mufflers to the standard GT trumpet exhausts. Rather than the original dual-point distributor, we added spark with an electronic MSD unit with mechanical advance and a Flamethrower coil. Other additions involved replacing base 289 motor mounts with K-code motor mounts and installing a K-code harmonic balancer and high pressure oil pump with the larger Cobra oil pan. Classic 1965 Cobra valve covers provided the final touch.

The result is a luxury GT Mustang wrapped around the performance drivetrain of a GT350, and it runs and drives like a sports car.

For those who have never driven a Cobra or a Mustang outfitted with the high-performance 289 engine (I hadn’t), it’s a revelation. Whirring solid-lifters and a shorter axle make for a noisier drive than in ordinary Mustangs, but the snarling throttle response, ability to rev beyond 6000 rpm, and strong acceleration pull at any speed are exciting, even half a century later. Rebuilt this way, a Mustang that had been a pretty but sedate commuter now steers, brakes, corners, accelerates, and sounds like a performance sports coupe. I’m a convert.

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