By 1968, the Ford Mustang->ke428 had already become one of the most popular cars in the United States. Affordable, available in three different body styles and with a bevy of inline-six and V-8 engines, Ford->ke31's pony was enjoying tremendous success. The arrival of the beefed-up Shelby Mustang and its many versions only made things better, but Ford and Carroll Shelby felt the pony could become even more impressive. Their dream came true in April 1968, when a brand-new version of the 428 Police Interceptor engine was fitted with improved-breathing heads and larger exhaust manifolds, giving birth to the 428 Cobra Jet. The mill quickly found its way into the Shelby GT500->ke1359, which became the GT500 KR or "King of the Road". Officially rated at 335 horsepower, but actually powered by no less than 400 ponies and 440 pound-feet of torque, the King gained iconic status almost immediately.

The moniker was discontinued for the 1969 model year, only a few months before Carroll Shelby terminated his agreement with Ford. The GT500 KR nameplate returned exactly 40 years later on the fifth-generation Mustang, this time adorning a 540-horsepower muscle car->ke507 that was motivated by a 5.4-liter V-8. After all of these years, the first-generation GT500 KR is as formidable as it's always been, but its statute and value have grown considerably in the eyes of muscle-car aficionados and collectors alike.

Updated 07/23/2014: A very rare Mustang GT 500 KR is being offered by RK Motors Charlotte for a price of $189,900. Click past the jump for more details.

Click past the jump to read more about the 1968 Shelby GT500 KR

Exterior

Like all 1968 Shelby Mustangs, the "King of the Road" benefited from a restyled, fiberglass front end with twin hood scoops and louvers. Details that made it stand out from a pack of Shelbys included "Cobra Jet 428" emblems on the fenders, dash and gas cap lid, and "GT500 KR" graphics on the front fenders.

All KRs came fitted with either Lucas or Marchal fog lamps in their front grille openings, Ford Thunderbolt-sourced taillights, chrome bumpers, a twin-exhaust configuration and contrasting Shelby stripes above the side skirts. Shelby built the GT500 KR in both fastback and convertible body styles. Only 318 drop-tops were assembled, as opposed to nearly 900 coupes, making them awfully rare and expensive nowadays.

Like most Mustangs, the Shelby GT500 KR was available with numerous options. Additional exterior features included various special paints, stripe packages and tinted glass.

Interior

Although it received several updates for 1968, the Mustang's interior remained familiar and kept its dashboard configuration almost unaltered. Naturally, the Shelby version gained unique features of its own, including a Cobra->ke2263-badged steering wheel, a striped gear shift knob, and Cobra-embossed leather.

Options included a Sport Deck rear seat, power steering, tilt-away steering column, air conditioner, and an AM radio, most of them also available on the standard Mustang.

The Interior Decor Group added even more features to the GT500 KR's interior, including Comfortweave upholstery, molded door panels with wood inserts, a three-spoke Rim-Blow steering wheel, and high-back bucket seats. The latter were introduced on the regular Ford Mustang starting 1969.

Drivetrain

The Shelby GT500 KR wasn't called "King of the Road" for nothing. Under its long hood lied Ford's most powerful engine for the 1968 model year -- the 428 Cobra Jet. The 7.0-liter V-8 packed about 400 horsepower and 440 pound-feet of torque once it rolled off the assembly line and revved up to 5,600 rpm, but Ford underrated its output at only 335 ponies. likely for insurance purposes.

Mated to a Toploader four-speed manual transmission, the mill was powerful enough to send the GT500 KR flying from 0 to 60 mph in only 6.5 seconds and up to a top speed of 140 mph. For 1968, these were some amazing figures.

The engine also found its way into the Mercury->ke55 Cougar, Mercury Cyclone and Ford Fairlane models, all of which have become icons in their own right.

Suspension and Brakes

Keeping the Shelby GT500 KR on its best behavior is a setup comprising a double A-arm suspension up front and sturdy leaf springs in the rear. It may sound a bit surprising for a high-spec Mustang to lack a sporty suspension, but, back in the day, the track-prepped GT350 was the only Shelby muscle car to benefit from such privileges.

Braking power was provided by power disc brakes on the front wheels and regular drum brakes, standard at the time, around back. Handling both power and braking were a set of E70-15 Goodyear Speedway 350 tires. That's some highly sought-after rubber among present-day muscle car collectors.

Prices

The Shelby GT500 KR retailed for around $4,500 back in 1968, making it pretty much affordable given its enormous power and features. Of the 4,500 Shelby Mustangs built that year, around 1,200 were GT500 KR's, which is why these ponies fetch more than $150,000 in tip-top shape and often go for more than $300,000 depending on model, specs, and number of original, unrestored parts. Needless to say, the 1968 GT500 KR is one of the most collectible 'Stangs of all time.

The Wimbledon White model in the pictures you see here is for sale through RK Motors for $189,900 and has just over 98,000 miles on its ticker.

Competition

Chevrolet Camaro

By 1968, Chevrolet->ke199 had already introduced and perfected the Camaro->ke248 as an outright rival to both the Ford Mustang and the Shelby GT500. However, no factory Camaro came equipped with an engine larger than 6.5 liters, with the most powerful being the 350-horsepower Z/28. The only competition for the GT500 KR came from dealers such as Baldwin-Motion or Yenko, who offered the big-block, 7.0-liter V-8 as a dealer-installed replacement for the factory engine found in both the SS and the Z/28. Baldwin and Yenko Camaros were known to produce in excess of 400 horsepower.

Next year, Chevy's COPO program led to the introduction of the Camaro ZL1, which carried an all-aluminum, 7.0-liter V-8 specifically designed for drag racing. Rated at 430 horsepower, these Camaros were capable of more than 500 ponies by means of exhaust modifications and further engine tuning.

Conclusion

Very few Mustangs are rarer than the 1968 Shelby GT500 KR. With only 1,200 units built in less than a year, the "King of the Road" is usually a show stopper during today's Mustang auction events, being superseded only by few GT350s and other high-spec, optionally-equipped ponies. Relatively cheap compared to other high-performance engines available in the late 1960s, the 428 Cobra Jet option reached an unmatched level of notoriety rivaled only by Chevy's ZL1 and Chrysler's HEMI mills. Very few engines have managed to reach the heights of the Cobra Jet, but thanks to dedicated collectors and restoration companies we can still enjoy, and some of us even drive, this outstanding muscle cars nearly 50 years since their inception.