The 428 CJ was offered in Mustang fastbacks and coupes (and in Ford Torino and Mercury Cougar and Cyclone models) with a four speed manual or three speed automatic. All 1968 Ford Mustang 428 Cobra Jets had beefed up front shock towers and Goodyear Polyglas F70X14 tires. Four speed cars had staggered rear shocks. The standard axle ratio was 3.50, with 3.91:1 and 4.30:1 ratios available.

All 1968 Ford Mustang 428 Cobra Jets came with GT level trim including front fog lamps and a side "C" stripe, but the only other external clue to the armament within was the black scoop and hood stripe. The entire package cost about $500, including front disc brakes. The Equa-Loc differential ($79) and Competition Handling Package ($62) were wise extras.

With 11.5 second ETs at 120 mph, the factory team of eight specially prepared 1968 Ford Mustang 428 CJs obliterated everything in their Super Stock class at the '68 NHRA Winternationals. The impact was no less forceful on the street. "The entire world will come to recognize this engine -- the 428 Cobra Jet -- at the pop of a hood," declared Motor Trend. Finally, thanks to the  428 Cobra Jet, the competition was chasing the Mustang. 

The 1968 Ford Mustang 
428 Cobra Jet 
Specifications
Wheelbase, inches: 108.0
Weight, lbs.: 3,620
Number built: 2,822
Base price: $3,600 

Standard Engine
Type: ohv V-8 
Displacement, cid: 428 
Fuel system: 1 x 4 bbl. 
Compression ratio: 10.6:1 
Horsepower @ rpm: 335 @ 5400 
Torque @ rpm: 440 @ 3400 

Representative Performance 
0-60 mph, sec: 5.4
1/4 mile, sec @ mph: 13.9 @ 103 

Super Cobra Jet

The 428 SCJ was first introduced during the 1969 model year. Mustang buyers who ordered either of the optional 3.91:1 or 4.30:1 rear end gear ratios got much more. Ordering either of these axles automatically triggered a few other upgrades as well, including the 428 Super Cobra Jet engine, an external oil cooler mounted in front of the radiator, and relocation of the driver's side horn to the passenger side of the radiator core support to make room for the oil cooler. Starting in February 1969 this complete package could be ordered as the "Drag Pack" option. Note that it was not possible to order an SCJ engine by itself -- the only way to get your hands on an SCJ in a Mustang was to order the optional 3.91:1 or 4.30:1 rear end gear ratios.

The strength of the Super Cobra Jet engine was based on  more  durable internals, including the  crank, rods, pistons, flywheel / flexplate, and harmonic balancer. These special components were  designed to withstand the higher RPM requirements of drag racing. For example, the SCJ used race proven 427 "LeMans" capscrew connecting rods, whereas the standard CJ rod used a more common press fit bolt and nut to retain the rod cap. The SCJ timing pointer is slightly longer to clear the larger harmonic balancer.

Connecting rod research seems to indicate that CJs used a variety of common high end FE rods, with the C7AE-B rod being fairly common.  Others have reported finding C6AE-C, C6AE-D, and C6AE-F rods in what they believe to be original engines. There is also  reference to a C9AE-C rod being used, but nobody has been able to confirm an installation. SCJs seem to use the C6AE-E rod most frequently.

A common misconception is that SCJs were originally equipped with forged pistons and CJs were had cast pistons.  Ford's "Muscle Parts Description and Interchange" book, a supplement to the original "Muscle Parts" catalog that was published in July 1970, clearly states that "all 428 engines use "dished" cast aluminum pistons with two sets of eyebrows cast so they can be used in right or left bank."

It appears that Ford went through at least three piston designs during the 428 CJ and SCJ production run to address durability problems. The later piston, which appeared around December 1968, is marked "428" and "SUPER" and differs from the earlier pistons by having additional metal in the pin boss area. The "SUPER" mark does NOT mean that the pistons were used exclusively  in SCJs. Though different part numbers were used for standard sized CJ and SCJ pistons (perhaps to provide slightly different installation tolerances), most builders believe that the pistons were identical.

None of the parts of the 428 SCJ reciprocating assembly interchange with their 428 CJ counterparts. Mixing SCJ and CJ parts can cause severe balance problems. 
It's important to note that all other components of the SCJ engine do in fact interchange with the CJ engine. Block, heads, manifolds, etc. are identical. Some original SCJ blocks were stamped "super" on the front; if present, this marking was likely there to tell the original engine assemblers to use SCJ internals when building the engine. Factory horsepower and torque ratings were the same for both CJ and SCJ engines. Performance off the showroom floor doesn't seem to differ much at all between the two.

"Detroit Locker" Differentials

Most 428 Cobra Jet fans have heard of the "Detroit Locker" differential, a positive locking differential that was originally produced by Detroit Automotive Products Corporation (DAPCO) and is now available from TracTech Inc. Most of the published literature says that buyers of the locking 4.30:1 rear end gear also got a gear driven Detroit Locker instead of Ford's clutch packed Traction-Lok, but recent research claims that this is not true. Information documents Detroit Locker availability beginning around November 1969 (that's in the 1970 model year), implying that there may not have been any Detroit Lockers delivered by Ford during the 1969 model year. During the 1970 model year, "DETROIT LOCKER DIFFERENTIAL" appears on the invoice of vehicles that came with a factory installation.

1969-70 BOSS 429 MUSTANG

The Boss 429 is one of the most unique Mustangs made. Its  rarity, its engine, and the fact that so much effort went into modifying the basic Mustang to make the Boss 429 engine fit makes this rare bird highly desirable to collectors.

Visually, the Boss 429 sits lower than other 1969-70 Sports Roof Mustangs. And compared to the Mach 1 or Boss 302, it has an understated image; except for the Boss 429 fender decals and large hood scoop, the Boss 429 doesn't have any stripes, blacked out trim, wheel or rocker panel moldings, or even chrome dual exhaust tip outlets.

The Boss 429 Mustang was  designed to legitimize the Boss 429 engine for NASCAR racing through the usual ploy of production numbers. It would have been more logical to use the Torino, after all that was the body style used for NASCAR, but for image reasons, Ford decided on the Mustang instead.

All 429s were built at the Kar Kraft facility in Brighton, Michigan,  the same facility  used to build the Le Mans Ford GTs. Partially completed SportsRoof Mustangs originally intended to receive the 428SCJ engine were modified at Kar Kraft to accept the larger 429 engine.  Getting the Boss 429 engine to fit the Mustang's engine compartment  was  an obstacle. To do so, the shock towers were relocated outward by hand, and  the suspension was lowered and moved further outwards 1 inch, using spindles and control arms unique to the Boss 429. This made the Boss 429 handle much better than other big block Mustangs.

Other features included Boss 429 fender decals, a manually controlled hood scoop, a front spoiler that was shallower than the Boss 302 spoiler, color keyed dual racing mirrors, engine oil cooler, trunk mounted battery, close ratio four speed manual transmission, 3.91 rear axle with Traction-Lok, 3/4 inch rear sway bar (the first Mustang ever to have a rear bar), and chrome 15x7 Magnum 500 wheels with F60x15 Goodyear  Polyglas GT tires. All Boss 429s came with the Deluxe Decor interior, 8000 rpm tachometer, and AM radio.

The Boss 429 engine was a strengthened version of the production 429. The blocks have HP429 cast into the front of the block on the driver's side. They used four bolt mains, a forged steel crank, and forged steel connecting rods. The most important component of this engine is its aluminum cylinder heads which featured a modified Hemi type combustion chamber which Ford called "crescent." These heads used the "dry deck" method, meaning no head gaskets were used. Each cylinder, oil passage and water passage had an individual "O" ring to seal it. The Boss 429 used a single 735 CFM Holley four barrel carburetor on an aluminum intake manifold. 1969 versions used a mild hydraulic lifter camshaft; 1970 models got a mechanical lifter camshaft along with an improved dual exhaust system.

Each Boss 429 Mustang came with a KK sticker placed on the inside of the driver's door above the Ford Warranty Plate which signified Kar Kraft's production number. The first Boss 429 was numbered "KK NASCAR 1201" while the last 1969 is numbered 2059. Some Boss 429s may have this silver tape stripe missing; a small brass plate was substituted by Kar Kraft on a small number of cars.

Besides the Boss 302, the Boss 429 was the only other Mustang that had its Serial number stamped on the back side of the engine block assembly, on the inner front fender panels, on the transmission housing,  and on the chassis itself. Kinda makes it hard for fakes to escape detection.

1969 Boss 429 Mustangs were available in Wimbledon White, Royal Maroon, Raven Black, Black Jade, and Candy Apple Red. 1970 versions were painted Grabber Blue, Grabber Green, Grabber Orange, Calypso Coral, and Pastel Blue. All 1970 Boss 429s came with a gloss black painted hood scoop.

One would expect that the Boss 429 would have been a street terror  given its impressive specifications. However, in stock form, it only equaled the 428CJs performance due to the mild state of tune. Combined with the $1200 price tag for the engine, demand was dismal. Lucky for Ford, too.....they lost money on every one they built.

The usual after market bolt on modifications were extremely effective in waking the engine up. Similar in this respect to the Chrysler street hemi, modified versions really moved as intended. Car Craft magazine obtained 12.3 / 113mph standing quarter miles after undertaking just a handful of quite minor modifications to a production Boss 429.  429 equipped Nascar Torinos dominated the 1969 season after their introduction. However, Ford pulled out of racing before the start of the 1970 season and as a result the big motor was never developed to its full racing potential.

 

PERFORMANCE:
1969 Boss 429 Mustang
Engine:	375hp Boss 429 V-8
Transmission:	Four-speed manual
Axle Ratio:	3.91:1
Weight	3,870
Acceleration	Sec.
0-30 mph	3.2
0-60 mph	7.1
0-100 mph	13.6
Standing 1/4 mi	14.09 @ 102.85 mph
Top speed observed	118 mph
Source:	Car Life 7/69

429 Cobra Jet

In mid 1970, Ford replaced the 428 CJ with the newer 429 engine. The CJ and SCJ engines were not the Boss 429 engines.

The 429 was unique in many ways. It offered thin wall casting, longer bore centers than the FE block, huge bearings, and canted valve cylinder heads forming a slightly hemispherical combustion chamber. Rocker shafts were replaced with rockers riding on fulcrums with separate pedestals. The canted valve design angled the valves in the head, allowing  larger ports and valves. It also permitted an better mixture of gasoline and air into the chamber. 

 The 429 Cobra Jet package included:

• Bigger heads with larger ports and valves
• Stamped steel rocker arms
• Screw in rocker studs in the early 70 models
• Guide plates like used in the Boss 302's
• Compression was increased from 10.5:1 to 11.3:1
• Cast iron intake manifold
• Single 700 cfm Rochester Quadrajet carburetor
• Rated at 370 horse power

In 1971, Ford offered the 375 hp Super Cobra Jet 429. This upgrade offered:

• Four bolt mains
• Forged aluminum pistons
• Bigger oil  pump
• External oil cooler
• Cast iron crank shaft with higher nodularity than the base 429
• Mechanical camshaft with adjustable rocker arms
• Single 780 cfm Holley carburetor

1971 was the last year for the Cobra Jet engines. Performance was very similar to the 428 models. Times vary somewhat as you can see; it depends on how the car was prepared and who was driving. Most magazine road testers took it easy on the cars for fear of blowing them up.

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