In this edition of Muscle Car Milestone, we’ll focus on the 1969-1970 Ford Mustang Boss 429. In the late 1960s, Ford had grown weary of seeing Dodge and Chevy capture the checkered flag in NASCAR. Ford needed major firepower to go up against Dodge’s 426 Hemi and the big block Chevys, so the Boss 429 was created. In fact, this big block powerplant was one of the biggest engines ever placed under the hood of a Mustang. So, the question you may be asking is how well did the Boss 429 perform on the strip and the street? Let’s take a closer look and get to know the 1969-1970 Ford Mustang Boss 429.

The 1969-1970 Ford Mustang Boss 429 was built to satisfy NASCAR’s homologation rule that in order for Ford to race the 429 cubic-inch V8 engine on the track, 500 examples of the engine had to be built for the buying public. Oddly enough, Ford chose to install the engine in the Mustang instead of the Torino it raced. Also, Ford discovered that NASCAR mandates didn’t specify that the engine had to be installed in the car being raced.

1969: A Legend in the Making

One look at the 1969 Ford Mustang Boss 429 reveals one of the most aggressively styled Mustangs of its day. The new Boss 429 featured a massive, functional hood scoop, matte black chin spoiler, dual racing mirrors, and F60x15 wide-oval fiberglass belted Goodyear tires mounted to chrome 15-inch Magnum 500 wheels. The Boss was available exclusively as a Sportsroof fastback available in Raven Black, Royal Maroon, Candyapple Red, Wimbledon White, Blue, and Black Jade.

Inside, the Boss 429 included high-back bucket seats with Comfortweave knitted vinyl trim, a tachometer, and nylon carpeting. The Boss 429 also included deluxe seat belts, power steering, and a visibility group which included a lighted luggage compartment, glove box and ashtray, parking brake warning light, under dash courtesy light, and lighted ignition switch.

Ford partnered with Kar Kraft in Brighton, Michigan to build the Boss 429. Ford transported partly built Mustang SportRoofs to Kar Kraft who did the bulk of the work creating the Boss 429. To accommodate the size of the 429 engine, Kar Kraft had to make several modifications under the hood. For starters, the crew at Kar Kraft revised the front shock towers by moving them one inch forward. The upper A-arms were also moved out a half inch and lowered one inch. Furthermore, the lower A-arms were moved outboard to increase camber. The Boss 429 was also outfitted with heavy-duty shocks, heavy-duty front and rear stabilizer bars, and power front disc brakes. Due to the engine’s size, air conditioning wasn’t offered, a smaller brake booster was used, and the battery was moved to the trunk. All this specialty work came at a price since Ford lost money on every Boss 429 Kar Kraft built, even though the Boss 429 cost around $5,000.

The heart of the 1969 Boss 429 was, of course, a big block 429 cubic-inch, semi-hemi engine rated at 375 horsepower and 450 lb.-ft. of torque. Those in the know state this rating is somewhat conservative and the Boss 429 actually developed upwards of 400 horsepower. This powerplant featured full-flow exhaust manifolds, a forged steel crankshaft, and a high-rise intake manifold. This engine also featured a Holley 735-cfm four-barrel carburetor, high-capacity oil cooler, and a driver-controlled ram-air intake. The only available transmission was a close-ratio Toploader four-speed manual. A 3.91:1 ratio with Traction Lok was standard in the 9-inch rear axle. A 4.30:1 Detroit Locker was available as an option.

Car Life put the Boss 429 to the test in their July 1969 issue. The Boss ran from 0 to 60 in 7.1 seconds and sprinted the quarter mile in 14.09 seconds at 102.85 miles per hour. The editors took a shine to the Boss 429 stating “It is, quite frankly, the best enthusiast car Ford has ever produced. It ranks as one of the more impressive performance cars we’ve tested. Why? Because it does all the things such a car is supposed to do.”

1970: Back for Another Round

The Boss 429 returned for 1970, albeit with a few cosmetic changes. The Boss 429 now featured a revised front fascia with a dual headlamp setup and air inlets at each corner. The hood scoop was now painted matte black instead of body color. The color palette was also revised, and now the Boss was available in Grabber Blue, Grabber Green, Grabber Orange, Calypso Coral, and Pastel Blue. Inside, drivers now had a choice between black or white interior colors and a Hurst T-handle shifter replaced the stock Ford shifter.

The Boss 429 also received a few modifications under the hood. Changes included a solid lifter camshaft, revised Holley 735-cfm four-barrel carburetor, and a five-blade fan. The exhaust now featured straight-through piping opposed to the previous year’s cross-flow muffler.

Performance for 1970 was on par with the previous year’s numbers. The 1970 Boss 429 could run from 0 to 60 in 6.5 seconds and tear up the quarter mile in 14.0 seconds. Top speed was approximately 120 miles per hour.

Ford built approximately 857 Boss 429s in 1969 and only 500 in 1970, making these Sportroofs quite rare. This scarcity is probably one of the reasons the Boss 429 brings in a premium when they are offered for sale or auction. Currently, Hagerty rates a concours condition Boss 429 at $368,000 and a Boss 429 in fair condition at $126,000.

Sadly, the Boss 429’s time was short. NASCAR put the brakes on hemi-style engines with obstructive carburetor guidelines for the upcoming 1971 racing season. Ford baulked and pulled the Boss 429 mid-year from production. It was a good run and, unlike the Boss 302, the Boss 429 never made a comeback.