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To compete with the Mopar HEMI engine in NASCAR, Ford launched the BOSS 429 V8 in 1969. It was fitted in a limited production Mustang Fastback to meet the required homologation of 500 units. The result was one of the most desirable Mustangs ever to come from Ford.

Ford prepared the 429 for inclusion into NASCAR's Grand National Division. They modified a version Ford's big block V8 design known as the 'Ford 385 engine' and changed the stroke from 3.85 inches to 3.59. Built as a full-on race engine the exhaust ports were so large, it was nicknamed the 'Shotgun engine'.

Power was legally rated to 375 horsepower (280 kW) although 500 horsepower (370 kW) was possible. To meet emissions regulations, a mild cam was fitted along with a smog pump and small carburetor. With a few modifications up to 600 bhp was common.

Since the new engine was too large to fit in standard Mustang body, KarKraft was hired to modify the front-end of the car. They took a 428 Mach 1 and changed the inner fenders, widening the shock towers, to made additional space. A smaller brake booster was fitted and air conditioning wasn't offered.

Although the fastback was a striking design, Ford refrained from the large stripes and lettering found on models like the 302 and Mach 1. Instead a small BOSS 429 decal was fitted on the fender and a huge front scoop was used on the hood with manually-controlled butterfly valve.

The car was only produced for two years. In 1969 cars could be ordered in Raven Black, Wimbledon White, Royal Maroon, Candyapple Red, and Black Jade. in 1970 the hood scoops were painted black and the exterior colors were Grabber Orange, Grabber Green, Grabber Blue, Colypso Coral, and Pastel Blue.

Sales

Sold by Barrett-Jackson at the 2009 Scottsdale Auction for $183,700 USD. Described as "Kar Kraft NASCAR #1748. This is a car Ford engineers had in mind before the smog and insurance people had their way. This one should be enjoyed, but responsibly. It is a handful. This monster BOSS has been built to run like the original NASCAR's before Ford had to choke them down for street use. This BOSS sports the correct, date coded Holman Moody race parts that were used by the Ford NASCAR teams. The intake is a real Holman Moody Spyder single plane fitted with a vintage 1150 Dominator carburetor with numbers matching heads. Has the 1970 mirrored high Nickel Ford casting replacement block with the "R" in the lifter valley. These were real race blocks. These were the best 429 BOSS blocks ever produced. It comes with Dyno sheet at 674hp before the custom headers were added give it at least another 30hp running it up to 704hp on pump gas. The custom-built ceramic coated headers were over $5,000 to build with receipts. It was built and dynoed by R&R Performance. Documented with a Deluxe Marti Report. It also comes with a 3-ring binder, a box full of receipts, many books and info. The paint is absolutely beautiful. The body is rust free and is in excellent condition with the original Buck Tag and serialized fender aprons. The interior is also in mint condition. It is streetable and street legal. No part of the body is modified. This BOSS is built to run hard and last a long time. Nothing on Earth sounds like this BOSS with its 3" exhaust all the way back. On the street or at the shows, this BOSS gets a lot of respect and attention."