Our buildup started out life...
Our buildup started out life as a two-bolt 351C block. The block was bored .030 over by L&R Engines to accept new forged pistons.
When you mention the word Boss around almost any Ford fanatic, chances are the first thing that comes to mind is the Boss 302, usually followed by the Boss 429. Rounding out the top three (if it comes up at all) is the Boss 351. This seems odd as the Boss 351 is without a doubt the best street engine of the Boss trio and is arguably the most powerful small-block ever offered by Ford. Sure, the later Modular engine easily topped the '71 Boss 351 for sheer output and performance, but it took nearly 30 years to topple the king.
Blessed with essentially the same cylinder heads and cam profile as the Boss 302, the Boss 351's additional displacement and compression allowed the engine to take advantage of the huge port volumes and flow potential of the Cleveland heads without resorting to stratospheric engine speeds. Let's face it, the Boss 302 was built strictly to legalize the combination for the hotly contested Trans-Am series. Although effective at high rpm for racing, it was not an ideal street combination. Ditto for the stock Boss 429. Built for NASCAR, the Boss 429 was not much of a performer when strangled by the smallish four-barrel carb and stock exhaust system.
A cast 351C crank was polished...
A cast 351C crank was polished and made ready for action in the freshly machined block. New Clevite bearings were used on the standard crank.
There are a couple of reasons why the Boss 351 takes a backseat to the more popular Boss 302 and 429 models. For one, Ford spent a lot of money racing and promoting the Boss 302 in Trans-Am. Books have been written about the exploits of the smaller Boss engine in the hands of Parnelli Jones and George Follmer. Their 1970 Trans-Am championship in Bud Moore Mustangs cemented a place in automotive history for the Boss 302, not to mention a place in the hearts of blue-blooded Mustang owners. When the SCCA lifted the restriction on destroking factory engines in 1970, Chevy responded by offering the larger 350ci LT-1 in the new-for-'70 Z/28. Ford followed suit in 1971 by offering the similar-sized Boss 351.
While most enthusiasts of the muscle car era will tell you that 1970 was officially the end of the high-compression small-blocks, the '71 Boss 351 was still sporting 11.0:1 compression (Chevy dropped the compression of the '71 LT-1 to 9.0:1). Historians also consider the 1970 season to be the high-water mark of the Trans-Am series. The new styling of the '71 Mustang seemed to be a love-it or hate-it affair for Mustang enthusiasts. Combine this with ever-tightening emissions regulations, rising fuel prices, and the upcoming fuel shortages and it is easy to see why the Boss 351 takes a backseat to its more popular brethren.
The factory 351C rods were...
The factory 351C rods were freshened up as well. The big and small ends were machined and the beams polished and shot-peened for added strength. The rods also received new ARP2000 rod bolts.
Despite what amounts to a public relations problem, the Boss 351 has all the credentials of a true muscle car. That it was born in 1971 instead of 1969 means it will forever fight the uphill battle for recognition, but that doesn't make it any less of a solid performer. Compared spec to spec, the Boss 351 easily out-performed the more popular Boss 302. The two shared identical cam specs and head flow, but the Boss 351 offered higher static compression (11.0:1 vs. 10.5:1) and more sheer displacement.
Both Boss combinations offered aluminum high-rise, dual-plane intake manifolds, but the Boss 302 was topped off by a 780 Holley where the Boss 351 intake was sporting an Autolite 4300-D carburetor. The higher compression and increase in displacement was the main advantage for the Boss 351. The Cleveland heads were designed with racing in mind, but this made them less than ideal for a small-displacement street engine. The 351 was much better suited to take advantage of the port volume and ultimate flow potential. On the street, torque is king and the extra 1/2-inch stroke offered as much as 80 ft. lb. over the smaller 302 in the lower rev ranges. Even if both engines produced the same peak power, it is hard to ignore the extra 80 ft. lbs. of torque while accelerating through the usable rev range.