Boss 429 and Boss 351 Mustangs
1970 Boss 429
While the Boss 302 was made to win SCCA's TransAm series and the 428 Cobra Jet was made to win NHRA drag races, the Boss 429 was designed to beat Chrysler's 426 Hemi in NASCAR stock car racing. Although Ford Talladegas and the Mercury Cyclone Spoiler IIs were supposed to receive the Boss engine in 1969 for homologation, delays in the Boss 429 production forced Ford to look for another chassis to homologate the engine. This freak timing brought forth the Boss 429 Mustang, which in my opinion was a hack job to satisfy rules requirements rather than a super car born out of good development. Kar Kraft (car tuner owned by Ford) had to shoehorn the highly detuned Boss 429 engine into the Mustang Fastbacks by pounding out the shock towers by one inch. Although the Boss 429 engine would prove to be a performer by capturing NASCAR Winston Cup and Driver's Championship in 1969, the nose-heavy, highly-detuned street Boss 429 Mustangs were destined to become trailer queens, as the 428 Cobra Jet Mustangs were faster, and the Boss 302s were nimbler. The car did have potential if properly developed, but the Boss 429 Mustang mystique came more from its unusual history and rarity than from its racing heritage.
1971 Boss 351
The Boss 351 was the last of the first generation Boss Mustangs. The engine, a beefed-up 351 Cleveland small block, was an evolution of the Boss 302, with a longer stroke for better low rpm flexibility and 11:1 compression ratio. This was perhaps the perfect race engine for 1971, as NASCAR was thinking about imposing a 366 ci displacement limit, while TransAm officials threw out the 5 liter (305 ci) displacement rule. Alas, Ford decided to drop out of racing on November 1970, to focus engineering efforts on emissions, which did not allow the Boss 351 to earn a racing heritage of its own. However, the Boss 351 was an excellent street performer even at 3450 lbs, capable of 0-60mph in 5.8 seconds and 1/4 mile in 14.1 seconds at 100.6 mph. Because of its versatile performance and small production numbers (1806), the Boss 351 is one of the most desirable muscle Mustangs.
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