The Boss 429 Mustang
Last Updated June 13, 2023 | Meghan DrummondThe Boss 429 Mustang, like its Boss 302 sibling, was first created in 1969 and was only produced through 1970. In those two years only a few Boss 429s were created, but its legacy far outshadows its numbers. The Boss 429 became an automotive legend due to its impressive performance specs and appearance.
Designing the Boss 429
Both the Boss 302 and Boss 429 were created for homologation. Most racing divisions required manufacturers to produce and sell a set number of production vehicles. This kept manufacturers from creating impossibly expensive race cars that didn’t resemble their production line-up. It also led to some very interesting cars, like the GT350 and Boss Mustangs, being sold to the general public.
While the Boss 302 was designed to homologate the 302 CID engine for SCCA racing, the Boss 429 was built as a NASCAR challenger. The rules for NASCAR and SCCA racing homologation were different, which led to many of the differences between the Boss 302 and Boss 429. NASCAR required fewer cars to be produced, 500 to SCCA’s 1,000. NASCAR also didn’t require the engine and car to be developed together.
Design
Like the Boss Mustangs, Larry Shinoda’s time at Ford was brief. But he more than made it count. Larry Shinoda designed both the Boss 302 and Boss 429, two of the most iconic Mustangs of all time.
Shinoda was a hotrodder and a designer. This gave him an intimate knowledge of the kinds of sporty enhancements drivers loved. In particular, Shinoda was in touch with young drivers who liked to go fast and tinker under their own hoods.
The Boss Mustang was the type of car Shinoda loved, and it was successful for all the right reasons. Like the Boss 302, the Boss 429 is full of performance enhancements that improved appearance as well as quarter-mile times.
The “Boss” name came from Shinoda’s evasiveness regarding the name of his project. When people asked, he simply told them it was the “Boss’ car.” The 429 references the cubic displacement of the engine.
Competition
The Boss 429 dominated the 1969 NASCAR season, getting a whopping 26 wins in the year. It probably would have continued to do so, but a leadership change-up at Ford meant stock car racing was no longer a priority.
Bunkie Knudsen, the boss Shinoda referenced, was the Ford executive behind the stock car racing push. With Knudsen out, Ford killed the stock car program as well.
Fortunately, the Boss 429’s accolades are well-documented.
- 0-60 mph in 6.5 seconds
- Quarter-mile speed of 14 seconds
- Top speed of 128 mph
The Boss 429 Engine
The Boss 429’s engine was a first for Ford. It used a hemispherical “crescent” combustion chamber. The design is actually more similar to a hemi engine than any of Ford’s existing line-up. Sometimes referred to as a “semi-hemi” the engine features several unique design features.
The real magic of the semi-hemi resides in the cylinder heads. These were made from aluminum. Traditional engine designs have a single coolant jacket around the cylinder. The semi-hemi featured separate cooling circuits for the cylinder heads and the engine block. This created a more even cooling system, with fewer hot spots.
The Boss 429’s official horsepower was listed as 375, and the torque as 450 lb-ft. It’s likely that the actual horsepower numbers were higher. The Boss 302’s dyno tested performance was roughly 25 hp higher than it was quoted at. Though some have claimed that the Boss 429 produced as much as 500 horsepower, this is incredibly unlikely. It’s true that Ford fudged their horsepower numbers to be a little lower for insurance purposes. But it’s nearly impossible to hide 125 horsepower. It’s more likely that the actual tested horsepower was in the high-300s.
The Boss 429’s engine had a lot of displacement and consequently, horsepower. Unfortunately, because of the engine’s completed size, additional modifications were needed so it could fit under the hood.
Every Boss 429 Mustang had its shock towers removed and replaced with specially designed and reinforced pieces. This increased the width of the engine compartment by two inches and allowed the engine to fit between the fenders. The engine still needed more clearance though.
Eventually, the power brake booster was thinned and the battery was moved to the trunk.
| Specification | Boss 429 Engine |
|---|---|
| Displacement | 429 CID (7.0L) |
| Bore and Stroke | 4.36” x 3.59” |
| Carburetor | 735 cfm 4-barrel Holley |
Boss 429 Performance Modifications
Additional modifications needed to be made to the Boss 429 so that it could put its remarkable engine to work. Many of these modifications directly parallel the ones made to the Boss 302 Mustang.
Suspension
The control arm positioning was moved to be both wider and lower. This was intended to help with cornering and handling. The restructured shock towers were braced to keep them tied to the cowl.
Heavy-duty shocks were added, as well as heavy-duty sway bars. The front sway bar measured at 0.94” and the rear sway bar at 0.62.” Power front disc brakes were a standard feature.
Transmission
The four-speed toploader manual transmission was the only option for the Boss 429. Unlike the Boss 302, which was available in both a close and wide-ratio transmission, the Boss 429 was only available in a close ratio version. It also came with a traction-lok differential with a rear gear ratio of 3.9:1.
Aerodynamics
Unlike the Boss 302, which had a lot of exterior modifications, the Boss 429 was relatively subdued. The 1969 Boss 429 had a slight chin spoiler and fake rear quarter scoops. A decklid spoiler and rear window louvers were both available as options.
Perhaps the most distinctive Boss 429 feature is a fully functional and extremely wide hood scoop.
Wheels and Tires
Like the Boss 302, the Boss 429 came with 15”x7” Magnum 500 wheels. The tires selected for these wheels were F60 wide oval tires. These wide tires and wheels necessitated changing the fender design for greater clearance.
1969 vs 1970 Boss 429 Mustangs
Though the Boss 429 was only available for two years, there were a few notable changes between those years.
Under the hood, the engine’s hydraulic lifter camshaft was swapped to a mechanical lifter camshaft. This had no notable effect on performance. Mechanical lifter camshafts have a simpler design that’s more appropriate for high-rev applications, which accounts for the swap.
The iconic hood scoop also changed. While before it was painted body color, for 1970 the hood scoop was painted with a low-glare black paint. This was especially pronounced since the color selection was increased for 1970 as well.
1969 Boss 429s were available in Raven Black, Wimbledon White, Candyapple Red, Royal Maroon, and Black Jade. For 1970, Grabber Orange, Grabber Blue, Grabber Green, Calypso Coral, and Pastel Blue were added to the lineup.
Finally, a Hurst shifter replaced the Ford shifter.
All told, 857 1969 Boss 429 Mustangs and 499 1970 Boss 429 Mustangs were sold.
Buying a Used Boss 429
The Boss 429 is one of the rarest performance models manufactured. Only 1,356 were ever produced, and not all of those have survived. Even in 2008, Boss 429s could fetch $375,000 at auction. In 2020, a 1969 Boss 429 sold for more than $550,000. The price is only going up with time, and that trend is likely to continue. Of course, that’s assuming you can even find a Boss 429 to bid on. The rarity and desirability mean that few ever even go for sale.
Classic Recreations has bought the rights to manufacture new Boss 429 Mustangs. The price for these starts right at $209,000, which isn’t bad considering it’s a new, 0-mile Boss 429 Mustang.
For the more budget-conscious Boss fanatic, building your own Boss from a classic Mustang is a more appealing option. In particular, if you can find a 1969 or 1970 Mach 1 Mustang to use as your base, your build should be very doable. The Mach 1 and Boss Mustangs share so many features that some have a hard time telling them apart.
From there, it’s easy enough to add the gorgeous hood scoop, wide bias ply tires, or an h-pipe for authentic sound. While it won’t be a “true” Boss, it will be yours.
Boss 429 Legacy
Unlike the Boss 302, the Boss 429 has never made a reappearance in Ford’s lineup. It’s rare for a vehicle to be able to secure a legacy for itself in only two years, but the Boss 429 did just that. It wasn’t just the NASCAR wins or the sporty looks, but the whole Boss 429 package that people still find appealing.
The Boss 429 and Boss 302 were both retired in 1970, though the Boss 351 debuted in 1971 for one year only.
Boss 429 Brochure
Image Credit: Creative Commons
