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Wal Marshall, NZMustang.com

  The Boss 429 is amongst the most sought after of all the early model Mustangs. Why are these cars so prized, and fetch such high prices ? 
The following article is just a brief summary of what is actually a richly detailed story.

Wimbleton White 1969 Boss 429


The BOSS 429 story is closely interwoven with NASCAR racing. In the middle to late 1960's Chrysler was dominating NASCAR racing with their radical new 426ci hemi powered racers. Ford needed a new weapon in this battle, and decided to take it to Chrysler by building a big block hemi engine of its own. Thus the Boss 429 motor was developed, and it was designed and built from the bottom up as an all out racing engine. However to use the engine on the NASCAR track, Ford had to first homologate a minimum number of engines into regular production cars, and the Boss Mustang was chosen for this. The new hemi motor was christened the Blue Crescent, but as the intake and exhaust ports in the huge alloy heads were so large, it was nick-named  the "Shotgun".

The Boss 429 intakes will almost swallow a tennis Ball!! Pic Mike Flanigan


Standard features of the new motor included very large alloy "hemi" heads, massive ports with huge 2.3 inch inlet valves, (the biggest ever fitted by Ford into a production engine), high strength cast iron block with four bolt main bearings, and forged steel crank and conrods.

As Ford itself was fully committed to other work, and the available time frame was very short, development and production of the Boss 429 Mustang was contracted out in Sept 1968 to a company called Kar Kraft, which was already developing the Ford Trans-Am Boss 302 race cars. 

Kar Kraft were faced with considerable obstacles in developing the Boss 429 Mustang, not the least of which was the fact that the engine bay was over 2 inches too narrow for the motor! They solved this with some radical surgery moving the entire suspension outwards a full inch on each side. This necessitated completely new reshaped shock towers, new widened strut tower brace, new top and bottom suspension arms, new heavy duty uprights, and heavy duty springs. A slim new power brake booster was needed to clear the big engine valve cover, and the battery was moved to the trunk to improve weight distribution. The rear suspension was beefed up with staggered shocks, heavy duty springs, and a thick rear stabilizer bar. The whole car sat an inch lower than a stock Mustang, and as a consequence, a special shortened front spoiler was fitted to preserve ground clearance.

The Boss 429 prototypes were put through the full battery of Ford acceptance testing, and had to pass emission testing as well as hot and cold environment running tests, to ensure the both the chassis and the engine were suitably refined for all normal driving conditions. What eventually emerged from the development process was not a raw racer, but a refined production vehicle. In fact the Boss 429 was seriously over-refined. In production trim the engine was choked down to only 375hp by a mild hydraulic cam, a tiny carb, and smog pump. 

  Boss 429 Motors fill the engine bay - completely!


In January 1969, Kar-Kraft started production of the 1969 Boss 429 at its purpose built facility at Brighton, Michigan. Cobra Jet Mustangs were diverted off the Ford Dearborn production line, and shipped to Kar Kraft, where they were partially disassembled and manually rebuilt into Boss 429's.  1969 production ran from January 1969 through July 1969. The original aim was to make 500, but total units produced in 1969 were 859. (This includes 2 - 1969 Boss Cougars). 

By the end of the 1969 production run, the story of the Boss 429 "Shotgun" Mustang had spread through all the Ford Dealers and demand was so high that another run of 500 1970 models was started in August of 1969. These were completed by December 1969. This extra production was not undertaken lightly as each car was produced at a considerable loss by Ford due to the amount of manual rework required in the conversion. 

69 Boss 429 in Royal Maroon. Pic Jerry Heasley

This brought total production for the Boss 429 Mustang including the two 1969 Cougars and two 1970 Quarter-Horses to 1359 vehicles. Each vehicle was assigned a KK 429 NASCAR production number, starting from KK-1201 running through to KK-2558. The KK number is located on a unique tag attached to the rear of the drivers door. 

All Boss 429's have a unique NASCAR KK # tag on the drivers door.


All the Boss 429 models had two very distinctive and unique visual features: the prominent front "BOSS 429" decals on the rear of each front fender, and a large hood mounted air-scoop with a manually controlled intake flapper valve. However as standard, the cars also came with full deluxe interiors, power steering, close ratio gearboxes, low ratio  3.9 Traction-Loc diffs, and 15 x 7 Magnum 500 wheels (with unique extended centre caps on the 69 models).

1969 models were available in Raven Black, Royal Maroon, Black Jade, Candyapple Red and Wimbledon White. All 69 interiors were Black. The 1970 models were available in three Grabber colours: Blue, Green, and Orange as well as Calypso Coral and Pastel Blue. Both black and white interiors were available. Also the 1970 models came with  black painted hood scoops (69s were body colour), rev limiters, semi deluxe interiors, and regular short centre caps on the Magnum 500's.

1970 Model Boss 429 had grabber paint option, and black hood scoop.


When released to the Motoring press for appraisal the Boss 429 was roundly condemned for disappointing performance ("struggles to beat a 428 Cobra Jet for acceleration" was a common comment), and for poor handling due to the large and heavy motor up front. 

In fact, while the big Boss handling was not a match for the nimble Boss 302, it was very much better handler than any other big block Mustang as a result of the heavier springs, lowered ride height, realigned front suspension geometry, increased front track width, heavy rear sway bar, and relocation of the battery into the trunk. Also, considering the state of tune the cars left the factory it was no wonder the car was a bit slow.  To partially address the performance problem, Ford changed the camshaft after car 280 from a mild hydraulic unit to a hotter grind solid lifter, and lightened the massive racing conrods to make the engine rev faster. This took the power output up to around 400 bhp, (although officially it remained at 375bhp). When this was combined with a drop in the diff ratio from 3.5 to to 3.9 the big Boss really started to perform. Throw in a few minor engine mods to help the big motor to breath a little easier, and it became a truly formidable performer. "Car Kraft" magazine obtained 12.3/113mph standing quarter miles after undertaking just a handful of quite minor modifications to a production Boss 429.

So the Boss 429 was truly a sleeping giant waiting to be unleashed. And that's just what happened on the NASCAR circuit in 1969 when Boss 429 engined racers completely dominated the season after their introduction. Sadly 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. Several Boss engined drag racers were also built, perhaps the most famous being the TASCA Mustang drag car featuring a hot alloy block Boss 429. This car was trailered around the country successfully taking on all-comers with blistering sub 12 second quarters.

The TASCA drag racing Boss 429 Mustang blew away the competition.


The Boss 429 is a limited production, hand built, and highly prized collector car today.  Although, because of severe detuning the production car was not the giant killer on the road that it could have been, the model most clearly demonstrates the high point in Ford's commitment to racing, with top examples today fetching in excess of US$250,000.

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