Shelby's Little Surprise

Back at the dawn of the musclecar era, a man named Carroll Shelby approached Chevrolet with a wild idea. He and a friend wanted to create a new kind of two-seat sports car using many Corvette components. In the end, GM brass finally decided not to participate. Chevrolet brass and engineers felt they would be competing against themselves if they became involved in the creation of another two-seat sports car.

Shelby’s plans lay dormant for a few years. He then approached Ford with the idea of placing a small-block V-8 engine into a beautifully designed, but underpowered, English roadster made by the AC Sports Cars Company. The AC Ace was smaller than anything produced domestically, and former bomber pilot and auto-racing veteran Shelby felt that here was a good platform for a new kind of high-performance car.

This time, the engine in question was the new 260ci V-8 introduced in the ’62 Fairlane. Shelby got the engines he wanted and, using a facility in Los Angeles, mated the new Ford small-block with the AC car. Thus began production of one of the most notorious sports cars of all time.

Although the first small-block Cobra used the 260, the 289 was soon adopted. The Cobra was then offered at selected Ford dealers. By the time these cars began to appear on the streets and road courses of America, there wasn’t much Chevrolet could do. Although the more powerful Sting Ray was a potent car, it was larger and much heavier than the little Cobra and, hence, in any kind of speed contest the smaller car usually trounced it. In 1965, Chevrolet introduced an advanced all-wheel disc-brake system for the Sting Ray and a new 396ci “big-block” engine. These improvements made the Corvette an even better car, but it still couldn’t keep up with the Cobra, as a rule. When the extensively redesigned 427ci version of the Cobra was introduced, the performance gap between the Corvette and Cobra opened even wider. With only 100 or so of the original big-block Cobras produced, they are very difficult to find and extremely expensive.

When the Mustang was introduced, Shelby immediately recognized that the characteristics of this interesting car gave it the potential to also be a great road-course contender, and the GT350 was born.

Indeed, the light weight and great balance of the Mustang made it one of the all-time great road racers. Let’s look at the very effective changes made to the ’65 Mustang by Shelby to create the GT350. Keep in mind the changes made by Shelby for the GT350 will work just as well on your Mustang.

Under the hood, all ’65 Shelby cars began with the K-code 289, which was relieved of its restrictive cast-iron exhaust manifolds. Tri-Y configuration headers were then installed. Although the cast-iron manifolds used on the K engine were the high-performance variety, they were still quite restrictive when compared to headers with individual primary tubes. These headers led to glasspack mufflers, and the tailpipes were terminated just in front of the rear wheels. This abbreviated tailpipe also helped reduce exhaust restriction. Exceptions to this were cars bound for California, Florida, or New Jersey, which received an exhaust system that led all the way out to the rear of the car.

On top of the engine, the usual cast-iron intake manifold was replaced with an aluminum high-rise unit designed to flow freely and reduce weight. In place of the Autolite four-barrel carb, a Holley R3259 four-barrel unit was installed, featuring a flow capacity of 715 cfm. Finned aluminum valve covers and an extra-capacity aluminum oil pan were also included. The 289 found in the GT350 street version was rated at 306 hp, a 35hp gain over the stock K-code rating of 271. Also made during the ’65 model year were about 36 racing versions, or R-models. These competition models were rated at up to 350 hp.

Behind the engine, an aluminum-case Borg-Warner four-speed transmission was installed, and this led to a 9-inch rearend, usually equipped with 3.89:1 gears. All GT350s for ’65 had the Detroit Locker differential, and several gear ratios were available.

There were many other differences between the regular Mustang and the GT350. While the V-8 Mustang came equipped with 14-inch wheels, the first GT350s were equipped with 16-inch wheels featuring slotted spokes; however, most of the ’65 GT350 cars had 15-inch spoked-style wheels. The good-looking Cragar spoke wheels were available as an option. Proven Koni adjustable shocks were used at all four corners.

Underhood, a Monte Carlo bar tied the shock towers together for enhanced front-end rigidity. On the ’65 GT350, the upper-control-arm pivot points were relocated 1 inch below the stock location for enhanced cornering performance. This change reduced body roll and improved the tire contact patch in corners, because more negative camber was made available. Rear suspension improvements included the addition of traction bars and travel-limiting cables for the rear axle. Correct traction bars for a GT350 are still available from Traction-Master, the original supplier to Shelby. To improve balance, most GT350s had the battery relocated to the trunk.

When compared to the standard Mustang in appearance, the GT350 had most Mustang emblems removed. The exception was one of the small Tri-bar Mustang emblems found on the front left grille. The standard gas cap also remained. A fiberglass hood was furnished complete with a functional hoodscoop. Some GT350 fiberglass hoods had a steel frame.

Tony D. Branda offers authentic fiberglass hoods for your replica project. Most ’65 cars were white and had blue rocker stripes proclaiming the designation GT350 directly behind the front wheel. Inside the street GT350, things looked fairly stock, with the exception of a pod-mounted tach and oil-pressure gauge. The R-model cars got an interior safety group that included a rollbar, a safety harness, a fire extinguisher, and plastic side and rear windows.

As you can see, all of the things done to the Mustang by Carroll Shelby were no-nonsense and effective modifications. There isn’t a single trick used by Shelby on the ’65-’66 models that you can’t duplicate for a similar effect. In the power department, he started with the already-potent K-code engine, so don’t expect your C-code 289 to jump to 306 hp with the addition of a four-barrel carb and headers. Your stock 289 will wake up nicely with these additions, but to approach the high power level achieved in the GT350 you’ll need additional hardware to stand up to the rpm required to produce this kind of power.

With all of the advances made in camshaft and hydraulic-lifter design, you might be able to avoid the solid lifters altogether and still enjoy the same rpm potential. Crane would be an excellent source for advanced-design hydraulic lifters and cam. Likewise, you’d want to have some type of improvement on the lower end, such as was incorporated in the K engine. A nodular-iron or steel crank would be desirable, as well as some improvement in main caps. The K-code main caps were a heavier casting than the normal 289 item, so you may wish to use them. Main-cap studs instead of bolts reinforced with a girdle would be a good and economical way to improve the lower-end strength on the engine you have. Remember, to achieve 300 hp with a 289, you’ll need to spin 6,000 rpm and have reliability good for 6,500, which was the redline on the GT350. ARP is a good source for an engine-stud kit.

For ’66, several things changed on the GT350. Leftover ’65 cars sold in 1966 had the lowered control arms. To reduce labor costs, the lowered arms were not found on the ’66 production cars.

Rear quarter-windows replaced the stock air extractors on ’66 models, and a GT350 gas cap was standard. The ’66 cars had a different style of rear traction bar, which mounted below the axle. All of the ’66 cars had rear-exiting exhaust. Leftover ’65 cars still had the 15-inch wheels, but the ’66 versions came standard with a 14-inch Magnum 500 wheel.

Shelby 10-spoke wheels in a diameter of 14 inches were available as an option, and some cars also came furnished with painted steel wheels. Also produced in ’66 were 1001 special models made for Hertz car rental. These GT350s had chromed Magnum 500 wheels, and were usually black with gold trim. Most of the Hertz cars came with the C4 three-speed automatic transmission. However, some Hertz GT350 cars were equipped with four-speed transmissions. In April 1966, a Paxton supercharger became an available option.

In ’67, the Mustang changed dramatically. Although the car looked similar to the ’66, there were no interchangeable body panels. With the new and larger platform, the Mustang would now accept a bigger engine. Hence, the Shelby cars were no longer restricted to a 289ci displacement, and it didn’t take long for Mr. Shelby to capitalize on the possibilities. For ’67, the GT350 continued to be based on the K-code 289. While the Paxton supercharger was still offered as an option, the big news for the ’67 Shelby was the introduction of the GT500.

This car offered a warmed-up FE 428ci “Police Interceptor” engine. Equipped with dual four-barrel Holley carbs, the big engine was rated at 355 hp. Due to production difficulties, a few of the ’67 GT500s reportedly got the 390ci engine. A handful of GT500s were made with the medium-riser 427ci engine. The exact number of the 427 cars made is not known, but an original 427-powered ’67 GT500 would be a collector’s dream come true.

While the ’65-’66 Shelbys were almost identical in appearance to the stock Mustang, the new Shelby cars looked very different from their Mustang brethren. A fiberglass extension was added to the nose of the car, making it look longer and lower. In fact, the good-looking addition added 3 inches to the overall length of the car. This required a special hood, which was made of fiberglass and equipped with a functional scoop. Hood retaining pins became standard equipment. Two large driving lights were mounted in the grille opening very near the centerline of the car. Some had the lights situated at the outer ends of the grille opening, depending on varying state laws. Out back, upper and lower scoops were furnished. Lower scoops were intended to function for rear-brake cooling, while the upper scoops were used in place of the now-ornamental sail-panel gratings found on the regular Mustang fastback.

All of these body modifications gave the new Shelby an outrageous look that still turns heads today.

In 1968, Shelby production ended at the LAX location and was switched to the A.O. Smith Company in Livonia, Michigan. Ford brass felt that better control of the Shelby operation would be possible at the Michigan location. The ’68 Shelby front end was restyled yet again, and with very nice results. The front end was again produced in fiberglass. The ’68 cars were furnished with a twin-scoop fiberglass hood. The GT500 still came with the Police Interceptor 428. Again, a few of the GT500s came with the 427 engine, this time the low-riser version. For ’68, the 427 could be had only with an automatic transmission. Some big news for the ’68 GT500 came later in the year when the Cobra Jet version of the 428 became available. This engine replaced the Police 428, and the cars equipped with the Cobra Jet engine became known as the GT500KR. The KR suffix stood for “King of the Road,” a moniker borrowed from a popular song of the time. The CJ 428 was rated at 335 hp, a very conservative figure, most likely provided to appease insurance companies. Most sources agree the Cobra Jet 428 cranked out around 400 streetable horsepower.

Other big news for the ’68 Shelby Mustangs was the introduction of a convertible body style for both the GT350 and GT500. The ’68 Shelby GT350 now came furnished with a four-barrel-equipped 302 V-8 rated at 250 hp, so the power rating on the ’68 small-block Shelby was down somewhat.

The last of the Shelby Mustangs were produced in ’69. The Mustang had been completely restyled and, hence, the new Shelby looked quite different as well. It differed in appearance from the production Mustang more so than in any previous incarnation. This time, fiberglass fenders joined the fiberglass hood. The Shelby Mustangs featured two 7-inch headlights and Lucas fog lamps mounted beneath the bumper. The distinctive-looking cars shared identical engines with the Mustang this time, with the GT350 coming equipped with the 351 Windsor, and the GT500 using the Cobra Jet 428.

Although the ’69 Shelby was a great car, over 700 units went unsold during the ’69 model year. The remaining 789 ’69 Shelby cars were updated with a 1970 serial number and sold as ’70 models. There were a number of factors working against the Shelby by this time. One was the tremendous success of the new for ’69 Mach 1 package. In fact, the Mach 1 was so popular that the venerable GT package was no longer even offered after 1969.

There were 10 different engines available in the Mustang for that year, including a 290hp 351 Windsor, a 320-horse 390 as well as the 428, and the new 385-series Boss 429; so there was no shortage of performance options available to the performance-oriented buyer. Certainly, the availability of the Mach 1, Boss 302, and Boss 429 hurt Shelby sales.

It turned out that 1970 was the last year for high-compression engines in Detroit, and the Big Three automakers were bracing themselves for the onslaught of new federal emissions regulations. The truth was that Detroit had other things to worry about at the end of the ’70 model year, and dark days for high performance descended over the land.

In the course of this short discussion, it’s plain to see you can duplicate many of the performance modifications Shelby made, especially to the ’65-’66 Mustangs. Shelby replicas are among the most interesting and worthwhile projects we can think of, and the end result will be a car with an excellent performance envelope and classic Shelby appearance. Even coupes and convertibles are fair game for these upgrades, and we’ve seen interesting examples of both. Should you desire to produce a replica, parts and services abound to help you on your way. Clearly, there’s room in the world for more cars that are replicas of these beautiful and historically significant Shelbys.