The wildest of the ponies, be they Mustang, Camaros, or Javelins, had to be the very limited production Boss 429. This was an engine designed and built almost exclusively for the racetrack. It was quite unlike any other engine built by Ford. Conceived to do battle with the Dodge/Plymouth on NASCAR'S super ovals for a chance to win the coveted Grand National Champoinship, Ford had to build 500 to be sold to the public to satisfy NASCAR'S homologoation rules. It didn't matter what car the engine was put into as long as the required number of engines were sold. With this in mind, Ford chose the Mustang sportsroof body to further the pony-car's performance image.
What Ford's engineers did was to take the 429 thin wall block used in the Thunderbird and full-size Fords, then added aluminum semi-hemispherical combustion chambers. A "twisted hemi" or "semi hemi" some called it. This configuration allowed for superior breathing, for the ports, intake passages, and the oval exhaust valves were gigantic. The valves themselves were set across from each other to form a crossflow cylinder head. A cast aluminum manifold mounted a single four-barrel Holley carburetor, while the valve covers themselves were designed for easy removal, as were the hemi-style plug locations. If only engineers would think of ease of maintenance today.
Everything underneath was heavy duty. It had to be, bearing in mind the engine size. To facilitate mounting into the Mustang, the engineers haad to move the front suspension outboard an inch to allow the upper A-arm pivot and spring tower to clear the valve covers. Wile they were working on this, it was decided to lower the inside attachment point an inch to enhance front-end geometry. As for the suspension itself, it derived from the Mach 1 competition set-up, but with ultrheavy-duty Gabriel shocks, fat front and rear stabilizer bars, and staggered rear shocks.
The body was much the same as the Boss 302 with the addition of the largest functional hoodscoop ever to grace a Mustang hood. A choice of six single body colors were offered: black, white, red, blue, maroon, and black jade. The only outward sign to denote the car's potential was a Boss 429 decal mounted on the front fenders behind the wheel openings. The tough four-speed manual transmission was Ford-built and floor-mounted, in an interior bordering on the luxurious.
Road tests found the street version Boss 429 slower in every respect when compared to a 428 mach 1. It took the 0-60 in 7.1 seconds and the standing quarter in 14.90 at a speed of 102.85. With a curb weight of 3560 lbs compared to the mach's 34320, this is understandable, but this engine was primarily designed for ultr-high-speed cruising at the NASCAR tracks. On the other hand, it is said that Ford guaranteed the quarter mile in 13 seconds. If this is the case, then the 429 obviously had to be set up right to do it. Certainly, none of the few magazines who tested the 429 approached 13 seconds, possibly because the car was tuned for the street.
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