7. Boss 351
The Boss 351 is a somewhat forgotten Ford engine they produced for one year only, in 1971. Despite its relative obscurity, this is one fantastic small block with unique construction and specific output. In 1971, they redesigned the Mustang with a new, bigger and heavier body. The legendary performance versions like the Boss 302 and Boss 429 were gone and only the Mach I remained from the previous years.
Ford felt the Mustang needed one specific, high-revving model that would deliver great performance despite the tightening emission standards that were killing horsepower numbers. So, Ford`s engineers prepared a 351 CID, 5.7-liter small block motor. They used Cleveland heads, a four-bolt block and a higher, almost racing compression at 11:1. Basically, the Boss 351 had the best of everything packed in a compact but powerful package.
The factory rating of the 330 HP was conservative and the Boss 351 produced close to 400 HP, all thanks to innovative engineering and the high-performance components they put into creating it. Ford decided to offer it in a Boss 351 model, but not to promote it through racing, which affected the sales and popularity. The production was low at 1,806 units, which are highly collectible today and can demand high prices.
The automotive press recognized the greatness and the potential of the Boss 351 engine when it came out, but Ford failed to translate it to higher sales numbers. Today, historians agree that the Boss 351 was the best of the best of Ford’s small-block muscle engines because it featured all the finest components in a compact package.