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The Boss of Bosses – 1969 Mustang Boss 429 - As with all muscle cars, the heart of the Boss 429 was the engine. Everything about the 429 was huge. The intake ports and large-diameter valves were large enough to keep these engines spinning up to 8,000 rpm. The intakes measured 2.28 inches and the exhaust valves were 1.90 inches in diameter. The mammoth hemispherical cylinder heads and rocker covers were aluminum (early versions were magnesium). The crankshaft was a forged-steel unit, which was statically and dynamically balanced. This engine was rated at 375 horsepower but that number was not even close to its potential.
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Ford used a Holley 735cfm carburetor mounted on an aluminum intake manifold. Engineers designed the cylinder heads without gaskets. Ford called this the “dry-deck” method. Instead, an individual rubber O-ring was used for each of the 21 oil and water passages inside each cylinder head. Another four stainless steel O-rings sealed the combustion chamber. A forged steel crankshaft spun in a four-bolt main bearing block. Despite the performance potential of these rare engines, Ford had to install the Thermactor pollution-control system. Other than “Boss 429” decals on the front fenders and a huge, manually controlled air scoop that sealed to the top of the air cleaner, there were no other emblems to show this was a special car. The 1969 cars, like our feature car, had dual front pipes leading to two “bullet” type resonators, that led to a single transverse muffler and into two turn-down tips. The battery was trunk mounted to improve weight distribution. Unlike the 1970 Boss 429s, the ’69 version does not have a rev limiter.
https://www.hemmings.com/blog/article/t ... -boss-429/