Wayne Cook
September 1, 2001
Photos By: Mustang & Fords Archives

The stakes were high for the '69 Trans-Am season. Both Ford and GM had eyes on the championship. Prestige and sales were the prizes. The '68 Trans-Am season had been a disaster for Ford. The new-design Tunnel Port 302 engines had come unglued all season long, in part due to oiling problems at high rpm. The so-called Tunnel Port heads had been designed for the new 302 to replace the relatively restrictive 289 Hi-Po heads, and featured huge 2.12-inch-diameter intake valves. These heads were so named because the pushrods "tunneled" directly through the intake ports, allowing for a larger port and a straight shot at the intake valve. The concept looked good on paper, but Ford engineers needed to rethink their design for a winning Trans-Am engine.

Chevrolet had introduced the Z/28 package for the Camaro late in the introductory '67 model year, and the GM camp was having success with the car. Although '67 Z/28 production was limited to 602 copies, the '68 sales year closed with 7,199 '68 Z/28s sold. The Z/28 used the durable Chevrolet small-block for power, specifically the 327ci engine equipped with a 283 crankshaft, for a net displacement of 302 ci. In the '68 season, Chevrolet walked away with the Trans-Am championship, led to victory by Mark Donohue driving a Z/28 Camaro. Something had to be done by Ford to counter the success of the Z/28, both at the track and in the showroom. That something came to be known as the Boss 302.

Instead of the nodular-iron crankshaft found in the Hi-Po 289, the Boss 302 came equipped with a cross-drilled forged-steel unit. Rods were the 289 Hi-Po units with 3/8-inch rod bolts for extra strength. Standard rod-bolt size was 5/16-inch. Boss 302 pistons gave a compression ratio of 10.5:1. The biggest factor in the great performance of the Boss 302 was the cylinder heads. The units employed on the Boss engine were borrowed from the new 351 Cleveland parts bin. Completely different from the new-for-'69 351 Windsor engine, the 351 Cleveland was not scheduled for release until 1970, so in 1969 these heads were a brand new development. Unlike the Tunnel Port heads, the Cleveland units employed canted valves in an arrangement similar to the 396ci Mark IV big-block engine introduced by Chevrolet in the '65 Corvette. The splayed valve arrangement allowed for superior breathing characteristics. For the Boss 302, gigantic 2.23-inch-diameter intake valves were employed, with 1.71-inch being the size on the exhaust side. In '70, intake valve size for the Boss 302 was reduced to 2.19 inches to enhance throttle response and create more torque at low rpm.

A solid lifter cam provided the musical valve clatter for which the Boss 302 Mustang is famous. A 780-cfm Holley four-barrel carburetor atop an aluminum intake manifold was standard induction. Other types of Boss 302 induction such as the infamous "Cross Boss" intake and Autolite inline four-barrel were successfully produced but were disallowed by Trans-Am racing officials.

Ford brass wanted the Boss 302 Mustang to be the best-handling American car made, and the task of making it so was given to Ford engineer Mark Donner. Under his supervision, the Mustang suspension was studied and numerous changes were made for the Boss 302. These changes included heavier springs both front and rear, with a larger-diameter front antisway bar. A rear bar was not included until '70. The rear axle got staggered shocks to help control wheel hop. Special Gabriel shocks and 15-inch wheels with fatter F60-15 tires were included in the Boss handling package. Reinforced shock towers and heavier spindles were used on the front suspension to withstand the additional punishment expected with hard street or racetrack use. All of this added up to a package good for nearly 1 g on the skidpad.

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A prominent player in the development of the Boss 302 Mustang styling was Larry Shinoda. Hired away in August 1968 from the GM camp where he achieved fame as the designer of the '63 Corvette Sting Ray, Shinoda was responsible for many of the significant design features found on the Boss 302. These features included the graphics as well as the spoilers and rear-window slats available optionally on the car. At the same time, Shinoda was also the one to remove other design ornamentation features found on the regular '69 Mustang such as the fake sidescoops and roof-pillar horse emblems.

For '69, the Boss 302 was available in only four colors: Bright Yellow, Acapulco Blue, Calypso Coral, and Wimbledon White. For '70, most Ford colors were available. In addition to the changes made in the regular Mustang, changes for the '70 model year to the Boss 302 were several. These included the addition of the rear antisway bar, cast-aluminum valve covers on the engine, and smaller intake valves.

Although the Ford Trans-Am effort for '69 ended in frustration, the '70 season saw Ford and the Boss 302 victorious, with the No. 15 car of Parnelli Jones ending up in the Winner's Circle.

The Boss 429 was developed concurrently with the Boss 302; however, its final production was done at Kar Kraft in Brighton, Michigan. The Boss 429 Mustang was designed and offered to the public in order to homologate the 429 engine for NASCAR racing. SportsRoof Mustangs originally produced to receive the 428 Cobra Jet engine were shipped to Kar Kraft for completion. To accept the larger engine, Kar Kraft lowered and moved outward the front suspension. Special spindles and control arms unique to the Boss 429 were used. Outwardly, these special Mustangs were identified by a Boss 429 fender decal. The Boss '9 also came equipped with dual racing mirrors, a front spoiler, a functional hoodscoop, and a trunk-mounted battery. An engine oil cooler, power steering, and front disc brakes were also included. The standard transmission was a close-ratio four-speed connected to a 3.91:1 Traction-Lok rear axle. Magnum 500 wheels sized 15x7 were standard and shod with F60-15 tires. It was a good-looking Mustang although less flamboyant than the Boss 302.

Under the hood, a beefed-up version of the 385-series 429 engine was used. The blocks featured four-bolt main caps and a forged-steel crank. Special-design aluminum heads were used and no head gaskets were employed on the engine. Instead, the cylinder bores were sealed by O-rings. The heads featured a modified hemispherical-shaped combustion chamber referred to by Ford as the "crescent design," and the Boss 429 engine became known as the Blue Crescent 429 in Ford circles.

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In '71, the Mustang was redesigned yet again. Now the car was larger and heavier than ever before. Even the wheelbase was lengthened to 109 inches, up 1 inch from previous incarnations.

Home-Brewed Boss
Those of you wanting to produce something different might be interested in concocting your own "homemade" version of the Boss 302. The durability of the Windsor block, combined with the flow capacity of the 351 Cleveland heads, either the two- or four-barrel version, can make an interesting and powerful combination. Keep in mind that, in 1969, the Cleveland heads were an advanced design for their time, which featured huge ports and valves. However, they were designed without the tremendous benefit of computer-aided testing. Hence, many of the newer cylinder heads made for the Windsor 302 will give you a more balanced power curve.

If you're bound and determined to go forward, keep in mind that even the 2V Cleveland head port size is large for a 302 displacement, so for a street-use engine we'd recommend going with the smaller 2V heads for better low-end power and torque. You'll need a special intake manifold that will mate the two engine types. Modifications to the cylinder-head cooling passages will also have to be accomplished. Pay attention to the piston and rod requirements as well, and you'll show up at cruise nights with something different.

Unlike the genuine Boss 302 block, the standard 302 item is a two-bolt affair, so you might wish to consider a stud girdle for the high rpm use expected with an engine with such large flow capacity.

As in '69, 10 different engines were available in the Mustang in '71, with the base engine being the 250ci inline-six. Several versions of the 302 were available, and all 351s for the Mustang in this year were of the Cleveland variety. Also offered in '71 was the Boss 351, which now replaced the Boss 302 and Boss 429 as the top-of-the-line performance Mustang. In November 1970, Ford withdrew all support for Trans-Am racing, so the necessity for a special engine displacing 302 ci was gone. Hence, even though a '71 Boss 302 was slated for production, the car never saw the light of day. The Boss 351 featured a 351ci Cleveland engine with a high compression ratio of 11.7:1. The solid-lifter engine was rated at 330 hp and came equipped with aluminum valve covers. Like the earlier Boss cars, a four-speed transmission and a 3.91:1 axle ratio were standard. Ram Air was featured on the Boss 351, as well as front disc brakes, heavy-duty suspension, and front spoiler. Boss 351 cars had the Mach 1 grille, but were identified by a Boss 351 decal affixed in place of the Mach 1 markings. Again, the Magnum 500 wheels in a 15x7 size were used, this time shod with Goodyear F60-15 tires.

The Boss series of Ford Mustang automobiles remains one of the most historically significant types of high-performance cars of any manufacture. Designed to be balanced and fast, the Ford dream of Trans-Am dominance was realized in 1970 when the Boss 302 rode to victory. Although the Boss 429 was a homologation vehicle designed to get the 429 Blue Crescent engine certified for NASCAR racing, in street trim it was delivered to the showroom floor in a relatively mild form. The Boss 429 Mustang remains one of the most underrated performance cars of all time. A few changes underhood turned the street Boss 429 Mustang into a nearly unbeatable barnstormer. Finally, the Boss 351 was a great high-performance car whose lifetime was cut short by the impending factors of emissions regulations and high insurance premiums. Sadly, for performance enthusiasts everywhere and for many years to come, the words "high performance" had a hollow ring in Detroit.