The most notable muscle cars in the country came in many forms and from many different manufacturers, but one of the biggest players in the muscle car war of the late 60s and early 70s was Ford with their ever-popular Mustang.

But as you know, just any old Mustang wouldn’t quite make our list of muscle cars you should know. That’s why we’re diving in even deeper to the history of the popular pony car this month, taking a look at the legendary Shelby GT500-KR of 1968.

Marketed as the “King of the Road,” the Shelby GT500-KR, released in the middle of the 1968 model year, was a product of both Caroll Shelby’s skills and Ford’s performance focus. Images: MustangSpecs.com

Making Giant Strides

After leading Ford’s Mustang over the 400ci threshold in 1967 with both a de-tuned race 427 and Police Interceptor 428 as engine options, the Shelby GT500 had huge shoes to fill in 1968.

While both potent engines returned for the GT500 for the 1968 model year, at least briefly, Ford introduced the legendary 428 Cobra Jet in April of that year.

For GT500s, that meant the Cobra Jet became the lead engine mid way through the car’s production, replacing the Police Interceptor option.

It’s worth noting that a handful of ’68 Shelby GT500s were equipped with 427ci engines from the factory, but these were manufactured prior to the 427 engine option being discontinued for the model and the KR model taking over for the regular GT500s.

While the Shelby GT500s received a new engine mid way through the model year, they also acquired a “KR” suffix, which designated each car as a “King of the Road” model.

The famed Cobra Jet engine not only powered the GT500-KR model, it also greatly contributed to the car’s worthiness as the King of the Road.

Many of the qualifications that made a GT500 a KR model came from the famed Cobra Jet engine lodged between its front fenders. And while this engine was shared with the regular 1968 ½ Cobra Jet Mustang, the KR came with special engine upgrades that set them apart, including a larger intake port with 2.6-inch intake valves and 1.625-inch exhaust valves, a cast iron intake, larger camshaft with a .481-inch intake, .490-inch exhaust, and 290-degree duration, and a single Holley four-barrel 735cfm carburetor. The GT500-KR also came with optional 12.5:1 drag racing pistons.

Rated at just 335bhp, the Cobra Jet engine fitted between the GT500-KR’s front fenders is believed to actually produce a hearty 400+hp.

Although factory specifications put this engine at just 335bhp at 5,600RPM, it is estimated that the engine was capable of producing more in the 400bhp range.

Backing the upgraded Cobra Jet engine was either a 4-speed Ford Top Loader manual transmission with an 11.5-inch clutch or a C-6 automatic, the same options available in the regular GT500s prior to the half-year mark. The KRs were also equipped with front 11.3-inch Kelsey-Hayes power assisted disc brakes, rear 10×3-inch drum brakes and Goodyear Speedway 350 E70-15 tires like the prior GT500s. This equipment went with both standard 15×6-inch wheels and optional 15×7-inch 10-spoke Shelby aluminum wheels.

For those GT500-KRs equipped with an automatic transmission, the standard rearend gear ratio stuck at 3.50:1 while manual-equipped cars could be bought with a standard 3.25:1 rearend gear ratio or optional 4.11 and 4.56 rearend gears at no additional cost. A Detroit Locker rearend or a Ford Traction-Lok limited slip rearend were also available options.

Every Shelby Cobra GT shared specific traits and performance upgrades, giving Ford the upper hand in the performance street car world when it came to their top-of-the-line Mustang pony car. Image: Ford Motor Company via The Old Car Manual Project

The Nimble KR

In addition to the upgraded engine, the GT500-KR also sported a note-worthy suspension system compared to its plane Ford counterparts.

Image: Ford Motor Company via The Mustang Source

Upgrades that came with all the Shelbys that year included front suspension systems with unequal arms, adjustable tube shocks, coil springs, and an anti-sway bar while the multi-leaf rear suspensions were made up of a live axle, tube shocks and semi-elliptical springs.

While the new super 1968 ½ Mustang was designated the King of the Road, the heavy 3,570-pound GT500-KR was no match for some competitive vehicles, including HEMI-toting Mopars, but through a canyon or curved course, the GT500-KR was notable not only for its handling capabilities but also the speed in which it could execute its maneuvers.

Still, the GT500-KR was capable of accelerating from zero to 60mph in 6.9 seconds and complete a quarter-mile pass in 14.04 seconds at 102.73mph. Its could also reach a top speed of 130mph at 6,100RPM.

Styling of a Performance Machine

The 1968 Shelby models were not only performance-driven machines, they were also restyled aggressors compared to the base Mustang models. This aggressive styling came mostly in the form of a redesigned fiberglass nose piece which featured either Marchal or Lucus fog lamps, and an optional fiberglass Ram Air hood with dual hood scoops.

The Shelbys also came equipped with aluminum rocker covers, an accentuated tail piece, and sequential turn signals.

The GT500-KR shared the Deluxe Mustang Interior with the traditional Shelby GT500, as well as more basic Mustangs ordered with the top-of-the-line interior option.

In addition to the more aggressive body design, the 1968 model year also brought about a first for Shelby Mustangs in the form of a convertible. This gave enthusiasts more options for their open-air pleasures.

Inside all of the 1968 Shelby Mustangs was the Deluxe Mustang interior, complete with Black or Saddle upholstery, wood-grain trim, and a console with Stewart Warner gauges and Cobra embossed top. Fastback Shelby Mustangs, including the KR, also featured inertia-reel safety harnesses attached to a padded roll bar.

Available options for the interior included air conditioning, tinted windows (required in air conditioned cars) and fold-down rear seats, which were only available on fastback models.

Down to the Numbers

While the Shelby name and performance features make the KR special, so too does the fact that it was a limited-run vehicle. In 1968, a total of 4,451 Shelby Mustang GTs were produced, 1,251 of those being GT500-KR models. Within that 1,251, just 933 were fastback models while a measly 318 were convertibles.

Back in the day, if you wanted a GT500-KR fastback, it would’ve cost you $4,472 while a convertible model would have set you back $4,594. This is quite the jump from the factory $2,602 and $2,814 price tags associated with base ’68 fastback and convertible models.

Now, with base ’68 V8 Mustangs valued in the low $20,000 range, you’d have to shell out quite a bit more than the 40-percent markup for a ’68 KR model, with several fastbacks currently listed through Hemmings for a whopping $150K. Some KR models have sold in recent years for up to $230K.

A first for the Shelby Mustang line, the 1968 convertible model opened up a whole new world of performance car options.

The classic first-generation Mustang was a force of its own, but with special models like the Shelby GT family of cars, Ford really stepped up the game for muscle car and performance enthusiasts, so much so that the Shelby name has stuck for all these years, with even modern fifth-gen cars being offered with Shelby and King of the Road ties. Guess that just goes to show just how iconic the original Shelby Mustang GT500-KR was in the world of performance machines.

Be sure to check back next month for another muscle car you should know!