BD,
The Cleveland engine was produced in the US for 5 years, from the summer of 1969 through the summer of 1974, and installed in Ford vehicles during the 1970 through 1974 model years. The motor was also exported to Australia during this time. Australian production of the Cleveland motor commenced in 1972, but US motors continued to be exported to Australia through the summer of 1974.
The Cleveland motor belongs to an engine series known as the 335 series, which also includes the 351M and 400. Cleveland motors produced in the US all displaced 351 cubic inches. Australia produced Cleveland engines in 2 displacements, both 302 cubic inches and 351 cubic inches.
The Cleveland engines produced in the US fall into 3 broad categories, with detail variations from year to year. Those 3 categories include a 2 barrel carburetor version with hydraulic camshaft known as the 351C 2V; a 4 barrel carburetor version with hydraulic camshaft known as the 351C 4V or 351 Cobra Jet; and a 4 barrel carburetor version with solid lifter camshaft known as the 351 Boss or 351 HO. The Pantera was equipped with the second category of motor, equipped with a 4 barrel carburetor and a hydraulic camshaft, so I shall focus on that motor from this point onward.
The 1970 and 1971 Panteras featured the 351C 4V motor advertised as having a 10.7:1 compression ratio (actual was 9.5:1), rated for 300 bhp in 1970, 285 bhp in 1971. 4V is reference to the 4 venturis, or barrels, of the carburetor. It had a small, equal bore 4 barrel carburetor of approximately 600 cfm capacity, a single point distributor and a very mild hydraulic lifter camshaft. The cylinder heads featured large valves, large ports and “closed” combustion chambers, and the cast pistons had flat domes. The engine block was equipped with only 2 bolts per main bearing cap. This engine is known in the US as the “M” code engine.
Near the end of the 1971 model year; the 351C 4V motor was replaced by a 280 bhp motor, known as the Cobra Jet, having a true 8.6:1 compression ratio. This motor had a larger spread bore carburetor of approximately 700 cfm capacity, a dual point distributor and a hotter camshaft with more valve lift and duration. The cylinder heads had the same large valves and large ports of the earlier motor, but featured “open” or hemispherical combustion chambers. The motor also shared the same cast, flat dome pistons of the previous engine. The harmonic balancer of this motor was substantially larger than that of the previous engine, and the block featured 4 bolt main bearing caps. Overall the Cobra Jet motor was a much better performing motor than the motor that had preceded it. This motor continued into production for the 1972 model year unchanged. In the US this motor is known as the Q code motor.
The Q code motor continued into production for the 1973 and 1974 model years, but Ford dropped the Cobra Jet name, and returned to calling it a 351C 4V. Four changes were made to the motor in order to meet stricter emissions regulations. The first of these changes was replacement of the cast flat dome pistons with cast “dished” pistons, lowering the motors compression ratio to a dismal 8.0:1. The second change was replacement of the large valves with smaller valves equal in size to those of the 351C 2V motor. The cylinder head retained the large ports in spite of the smaller valves. The third change was the addition of exhaust gas recirculation and the final change was to retard the camshaft timing by four degrees. Thus equipped, the motors power rating slipped to 264 bhp.
The M code & Q code motors have one rather serious flaw, Ford engineers equipped the motor with 2 piece valves, wherein the valve heads are induction welded to the stems. The valve spring retainers are captivated by multi-groove keepers designed with a small clearance between keeper and valve stem. The valve heads have a tendency to break loose from the stem, the keepers have a tendency to loose their grip on the valve stem, and the spring retainers have been known to split as well. When a motor drops a valve while operating, it most usually results in a ruined engine block and cylinder head, as well as other damage to the reciprocating assembly. Prudent advice is to have the valves, keepers & retainers replaced with better parts at your earliest convenience.
The cylinder heads of this motor represented the culmination of what Ford had learned during the total performance era of the 1960's, this was in fact the last push rod V8 designed by Ford. The Cleveland motor is capable of producing more power per cubic inch than any other American V8 designed during the muscle car era. The engine was so superior to other designs of the time, that in order to level the playing field in competition, Cleveland equipped race cars were penalized with higher minimum weight restrictions or restrictor plates between the carburetor and intake manifold.
The 351C 4V motor, with its giant port heads, was designed with one thing in mind, i.e. high performance. So when corporate Ford switched its focus to fuel economy and building safer vehicles, there was no longer a place for this motor in Ford's line up. Ford officially abandoned its racing program and dropped all high performance cars from its model line up, including the Pantera.
The Cleveland engine remained in production in Australia through 1982, where its fame as a performance engine, if anything, is even greater than it was in the US. Australia is a source for a great deal of the performance parts available today for this motor. DeTomaso's source for Pantera engines beyond 1974 was Australia.
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