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The Boss 429 V8 was offered in a production car for only two years, but its impact on the Ford performance scene has continued for decades.

When the Ford Motor Company unveiled its latest racing engine to the public in the autumn of 1968, a number of prospective names were offered up, including Blue Racer, Blue Crescent, Shotgun engine, and Twisted Hemi. But somehow the label that stuck was Boss 429—the same name as the only factory production car that ever used the engine. And while the Mustang Boss 429 was produced for only two years, the engine’s performance career has continued on for half a century.

The Boss 429 story actually begins here, with Ford’s 385 engine series, also known as the Lima V8, introduced for the 1968 model year. Under development for six years, the 385 was designed to replace two existing Ford big-block passenger-car engine families, the FE and the MEL, which each suffered some built-in limitations in architecture. The 385 series shared its 4.900-inch bore spacing with the MEL family, but otherwise it was an all-new engine.
Like the big-block Chevy and the Cleveland Ford, two more American V8s of the ’60s, the 385 employed a canted-valve cylinder head layout, with the intake and exhaust valves inclined 4-5 degrees and splayed 9 degrees. The 385 was produced in two displacements: a 429 cubic-inch version (4.36-in bore x 3.59-in stroke) for the ’68 Thunderbird and a 460 cubic-inch unit of 4.36-in x 3.85-in bore and stroke for Lincoln. (Reportedly, the 385 name is taken from the stroke of the 460 version.) A racing engine based on the 385 architecture was also under development, and when Semon E. “Bunkie” Knudsen left General Motors to become president at Ford in March of 1968, he threw his enthusiastic support behind the project.

The heart and soul of the Boss 429, you could say, is its combustion chamber design: a traditional hemi configuration, but with a twist. On a conventional hemi, Chrysler for example, the valves are deployed at right angles to the crankshaft centerline, or vertical in this photo’s orientation. But on the Boss, the valves (2.28-in intake and 1.90-in exhaust) were rotated counterclockwise around 30 degrees, mainly to improve the port angles—hence the name Twisted Hemi. Also, there were usually a pair of squish/quench zones on either side of the valves, as shown here. Some racing versions of the Boss head do not employ these compression pads, giving the chambers more of a pure hemispherical shape. Except for early prototypes and a few special castings made for nitro drag racing, all Boss heads are aluminum.
Another distinctive Boss feature: There are no head gaskets as such. Instead, a receiver groove was machined around the circumference of each cylinder (above) to accept a Cooper ring (aka WIlls ring) These rings were manufactured from hollow metal tube around .093-.096 inches in diameter, which collapsed around .016 inches when the head bolts were torqued down, sealing the cylinder and leaving a .010-in air gap between the head and the block. The sealing rings were earlier used on some British racing engines in the ’50s, and Ford tried variations of the setup on the DOHC Indy and Le Mans 427 engines before they were used on the Boss. To seal the oil and coolant passages, receivers were also machined to accept DuPont Viton O-rings. While the no-gasket system required extra care in assembly, it was essentially bulletproof.

This shop manual photo above illustrates the novel valvetrain hardware that enabled the Boss combustion chamber layout. Instead of a pair of rocker shafts, there was an individual pedestal for each valve, with short rocker arms for the intake valves, long rockers for the exhausts, and valve lash adjustment taken at the rocker arm. The sprawling valve train layout required broad, massive rocker covers, which gave the Boss V8 its distinctive, muscular look.

The Boss V8’s primary target, of course, was NASCAR, and here the engine is shown above with Ford factory drivers David Pearson, Cale Yarborough, Richard Petty, Lee Roy Yarbrough, and Donnie Alllison (clockwise from bottom). The engine made its NASCAR debut partway into the ’69 season on March 30 at Atlanta, where Cale Yarborough, driving a Wood Brothers Mercury, earned the Boss its first win right out of the box. Sharp engine builders could obtain 620 horsepower or more, reportedly. The Boss was the Ford NASCAR engine of choice until 1975 when the series reduced the displacement limit to 358 CID, ending the big-block era in stock car racing.
In the photo, also note the gigantic Holley four-barrel carburetor. Later named the Dominator in a customer contest, this carb, capable of processing more than 1000 cubic feet of air per minute, was jointly developed by Ford and Holley specifically for the Boss 429, and Ford racing teams enjoyed its exclusive use for a time. Later the design was turned over to Holley and marketed to racers of all makes.
To homologate the 429 CID hemi for NASCAR use, Ford was required to offer the engine to the public in a standard production car. So an assembly line (above) was set up in a former motor home plant in Brighton, Michigan, where Ford’s private performance contractor, Kar-Kraft, put together a limited run of Boss 429 Mustangs. A total of 1,358 cars were built, give or take, including 859 in 1969 and 499 for 1970. (The production run also included two Boss Cougars.) Priced at nearly $5,000, the Boss Mustang was expensive and exotic, excessively nose-heavy, and with its conservative road tuning and dinky 735 cfm carburetor, performed below its actual potential. Still, the rare Mustangs are highly prized by collectors today, with sound examples selling in the mid-six-figure range.

The Boss V8 also found its way into road racing, where a special 494 cubic-inch Can-Am version was developed with an aluminum block and mechanical fuel injection. Holman Moody and Alan Mann (shown) were among the teams that experimented with the Boss in the Can-Am series, enjoying limited success, and barely a handful of the big 494 engines were produced.
When the National Hot Rod Association overhauled its Pro Stock rules for the 1982 season, adopting a single 500 CID limit, Ford drag racers had no choice but to dust off the old Boss V8, out of regular production for more than a decade, and update it with ’80s technology. Multi-time champion Bob Glidden first tried the big V8 in a tiny Escort EXP chassis, but found it too stubby and unstable for the new rules. His Thunderbird and Probe-based racers were far more successful, winning five straight season championships from 1985 to 1989. But as technology advanced, Glidden’s Boss-based engine program grew increasingly obsolete. The family-operated team took its last national event victory in 1995, and Glidden retired in 1997 with 85 wins and 10 season titles.
The Boss 429 engine story isn’t over yet. Ford engine guru and perennial Engine Masters dyno competition winner Jon Kaase offers a Boss for the 21st century, if you will. The Boss Nine V8 (below) is based on Kaase’s own cylinder head castings, which sport the latest combustion and airflow technology. The package, designed to be both powerful and practical, has been re-engineered to use the standard (and widely available) 429/460 Ford cylinder block and conventional steel head gaskets. Buyers and builders can go the traditional carburetor route or use electronic fuel injection. Prices start at $23,500 for a complete engine and combinations with up to 1,000 normally aspirated horsepower are available.

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