1970 Boss 429 Mustang Concours Trailered Gold

1970 Boss 429 Mustang

What is more valuable, a 1967 Shelby GT500 or a 1970 Boss 429 Mustang? For the past four years now the Boss 9’s have brought more money at high profile collector car auctions around the country. They are just more rare because production numbers were so low. Ford only produced 497 of these rare Boss 9’s in 1970, the last year the Boss 9 engine was homologated for NASCAR.

This week Show Your Auto.com listed a Concours Trailered Gold 1970 Boss 429 Mustang for sale for one of their clients in Houton, Texas. The Boss 9 is in its original Calypso Coral paint, and is so accurate and original it was used as a benchmark instructional tool for Boss 9 judge and restoration authority, Ed Meyer.

Not only is it documented, but the paperwork on this one is considered “bullet proof.” It includes an original Bill of Sale, Kar Kraft paperwork, two dealer shipping invoices (Lois Eminger report), complete owner history and the Deluxe Marti Report. As for originality, the restoration is considered OEM intensive and it retains its entire original drivetrain. See ad for restoration photos.

The origin of the Boss 429 comes about as a result of NASCAR. Ford wanted a monster big block motor to compete with the the Mopar 426 Hemi in NASCAR’s Grand National Division. NASCAR’s homologation rules required that at least 500 cars be fitted with this motor and sold to the general public. Ford felt the Mustang would sell better with this new engine for factory production, although Ford Torinos would be chosen to compete using the Boss 9 engine in NASCAR.

1970 Boss 429 motor

The Boss 429 engine is a derivative of the base Ford 385 engine. It used four-bolt mains, a forged steel crank and forged steel connecting rods, and big-port, staggered-valve aluminum cylinder heads which had a modified Hemi type combustion chamber which Ford called “crescent shaped” combustion chambers. The aluminum heads were “sans gaskets” so they were referred to as “dry-deck.” Each of the cylinders had separate oil and water passage with “O” ring seals.

The Boss 429 engine used a single Holley 4-barrel 735 cfm carburetor mounted on an aluminum intake manifold. They all had Ram Air induction. Nice flow for that era. By 1970, the 429 got a mechanical lifter camshaft which was aided by a better dual exhaust system. The cars were rated very conservatively at 375 hp and 450 pounds per foot of torque. The engine back then retailed for $1,200, a very high price for a factory motor.

Ford chose to sell the Boss 429 engine in its Mustang line, creating one of the most powerful Pony cars of all time, and meant to be Ford’s answer to the Hemi Cuda. However the Mustang engine compartment was not wide enough for the Boss 429 engine so they contracted with an aftermarket company called Kar Kraft in Brighton, Michigan to modify the Mustang body to accept the monster Boss 9 engine. They used Cobra Jet big block Mustangs and made extensive modifications to include widening the shock towers through the inner fenders. The front suspension was modified to make room for the block and exhaust manifolds. The battery was repositioned to the trunk and a stiff 3/4″ sway bar was added to the rear end to improve handling. The Boss 9 was the first Mustang to ever be fitted with a rear sway bar, which is why it handled much better than other big block Mustangs.

Kar Kraft also added a manually controlled hood scoop, and a front spoiler smaller than the Boss 302, color keyed dual racing mirrors, and engine oil cooler. It came with a 3.91 rear end with Traction Lock. They boasted Polyglas F60X15 tires, quicker power steering and power front discs. Boss 9 Mustangs enjoyed the Deluxe interior decor and an 8000-rpm tach.

Air conditioning and automatic transmission were not available on a factory Boss 9.

Ford built 1,356 Boss 429 Mustangs and two Cougars for ’69 and ’70 before ending its factory racing program and retiring the legend. Today these Boss 9’s are among the rarest of muscle cars.

1970 Boss 429 Mustang

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