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Hey guys, the long post below is my reply to a series of negative comments regarding the 351C on another forum. The 351C has received a lot of negative opinion from within the Pantera hobby over the years. Although I've only scratched the surface, I thought you might find the the brief insight into the 351C's design I provided informative. Enjoy.
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Boss_351_Motor_II

Ford's literature says the 351C 4V's reason for being was (1) racing (2) a performance option for production cars (3) cost.

Its a racing motor. It was designed for 6 liter NASCAR racing, banging fenders with cars powered by 426 Hemis & Boss 429s. Let that soak in for a moment.

It was designed by the same guys who designed the 427 FE. The 427 FE featured a steel crank, thick bulk heads above the main bearings, cross-bolted main bearing caps, a main priority oil passage running down the side of the block. These engineers found those features necessary for the 427 FE to survive NASCAR racing.

These same engineers designed the 351C for the same type of racing yet they included none of those features.

Had they forgotten everything they learned? Had they gone daft? Were they idiots? You can't straddle the fence on this issue. They were either idiots and decided their new motor didn't need those features, or they were up to something new with the 351C 4V. Something very deliberate. The engineers knew they would have to contend with the same forces which required cross bolted mains, thick bulkheads, steel cranks and side oiling when they had previously designed the 427 FE.

I will admit that the lubrication system (comprised of only two oil passages) and the thin cylinder walls must have been budgetary compromises. I must also point out that some (not all) NASCAR teams, and some (not all) big name drag racing teams had access to heavy wall blocks (Bud Moore's blocks) and fully counter-weighted steel cranks (Moldex cranks). But more often than not, race teams went racing with production parts.

The 351C 4V benefited from the new ways of doing things the engineers had learned while designing racing motors such as the Indy racing motors of 1963 - 1965. Design of the Cosworth DFV Formula One motor was also wrapping up in England in 1966. The 427 powered Ford GT40 was dominating LeMans and the World Endurance Racing series in 1966. When design of the 351C 4V began in 1966 Bill Gays engine group was literally immersed in applying high technology in the design of racing engines. Ford literature from the era described the Cleveland as "an engine that reflects the racing heritage of Ford products on the worlds toughest race courses". To achieve the goal of building a potent and durable racing motor that could be mass produced as inexpensively as possible the team relied upon the use of engineered solutions, intelligent design and finesse rather than the expensive, heavy, brute force solutions that had been applied in the past when building Fords 427 FE of the mid 1960s.

One example of solving problems with finesse rather than brute force is the extra wide footprint of the 351C main bearing caps. The footprint gives them great stability without resorting to using cross-bolts. And it makes the 351C 4V less expensive to build along the way.

When the 351C 4V entered the scene in 1972, NASCAR was dominated by 7 liter endurance racing motors than cruised around the ovals at about 7000 rpm making over 500 bhp. Endurance camshafts of the day had about 0.600 inch lift.

It was no accident that when equipped with a 0.600 inch lift endurance racing camshaft the 351C 4V makes about 515 bhp at about 7000 rpm. From 5.75 liters! 7 liter hemi motor torque and horsepower from 5.75 liters at the same rpm.

Let that very deliberate fact soak in for a moment.

The engineers hit their mark dead on. No mistakes. No getting lucky. It was all very deliberate. The Cleveland is a very damn amazing racing motor. It just lacks the curb appeal of the hemi motors with their big aluminum heads & centrally located spark plugs.

There's a reason why even today its hard for modern alloy heads to improve upon the intake port flow numbers at 0.600 inch lift achievable with the iron 351C 4V head. That intake port was deliberately optimized for 0.600 inch valve lift. Some people have ignorantly referred to the intake ports of the 351C 4V as nothing more than big pipes for gulping air, inferring there was no intelligent engineering in the design. This is, of course, far from the truth. Ford literature from that era described the ports as “carefully sized”. The cross sectional area of the 4V intake port (3.14 square inches at the push rods) had been used in high performance FE engines since 1960; displacing 352, 390, 406, 427 and 428 cubic inches.

As the 351C 4V powered Fords thundered around the banked ovals at 7200 rpm for 500 miles, they did so with complete reliability. They were reliable in spite of their nodular iron cranks instead of steel cranks, in spite of their thin wall block instead of thick bulkheads, and in spite of their lack of cross bolting.  The engineers achieved the 351C 4V's reliability with all those short cuts because they weren't short cuts. Like the wide main bearing caps, the engineers deliberately chose engineered solutions instead of brute force to make the motor reliable. The 351C did not have a reputation for problems in the early years, excepting for under-lubricated rod bearings above 7000 rpm. Through 1973 all the press the 351C 4V received was "mostly" stellar.

1974 was the first year the 351C received bad press in the magazines. It was the year of the first oil embargo. It was the year everyone started buying intake manifolds with tiny runners, economy cams and headers with tiny primaries trying to improve the fuel economy of their V8s. It was the year that the sbc with its small ports began to dominate the aftermarket parts industry, helped along by a bunch of guys like Vizard & Yunick with vested interests in the little sbc motor. A magazine writer named CJ Baker was a significant source for the body of mis-information that grew up around the 351C 4V.

As is usual in motor sports, racers & teams kept pushing the limits. They were no longer satisfied racing at 7200 rpm and they began pushing the motors to higher and higher engine speeds. By 1977 they were cruising the ovals at 8500 rpm and admitted to making 570 horsepower. Quite a bit above the original design parameters of the 351C 4V. The problem was, US Ford abandoned racing in February 1973, and no further official development of the motor occurred after that.

Hank The Crank introduced a forged steel 351C 4V crankshaft in 1974. The crank was internally balanced, and fully counter weighted (8 counter weights). The additional counter weights were needed for racing above 7500 rpm. The crank also had relocated oil passages, which may hint at the possibility that the oil passages in the oem crank were suspected of being problematic.

Shortly after the introduction of the HTC steel crank the engineers at Ford authorized the manufacture of a thick cylinder wall & thick bulk head block in Australia. By the 1976 NASCAR season all Ford teams had access to fully counter-weighted steel cranks, and blocks with thick cylinder walls and thick main bearing bulkheads, ala the 427 FE. It's not unreasonable to assume the 8500 rpm engine speeds required these changes ... but iron has dampening properties that steel does not. There's equal evidence the steel crank necessitated the heavy duty block.

The HTC crankshaft was an aftermarket part. How many of us have had problems with our motors caused by aftermarket parts? Did the steel crank negated the engineering that went into the block? The nodular iron crank and the thin wall block were engineered to work together as a durable system.

So one person observes the design of the 351C and concludes the short block is nothing special, the castings are thin and flimsy and the head design is compromised. When I observe the 351C I conclude it is an AMAZING racing motor designed by a group of brilliant men. When the original castings are carefully assembled it is capable of making 500 bhp naturally aspirated at engine speeds up to 7200 rpm under NASCAR racing conditions (some of the toughest racing in the world) for a very long time.

-George

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Last edited by George P
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Forgive me for a question about the great Cleveland. I've been told by several that the oiling system is not adequate for more than approx 350HP, if you tune it above that, you need an external 6an hose from above the oil filter location to the oil pressure sender. It's supposed to compensate for the Cleveland's oil system that sends oil through the cam oiling system before main bearing 2-5. I have such a hose on my 2 Clevelands, and on one of them I just had a lifter collapse at high rpm, so right now I'm not sure it's a good idea.

Any views? I'm not critical of the Cleveland, I just want to know... Confused

The lubrication system is indeed a problem. It and the thin cylinder walls are two not so amazing aspects of an otherwise amazing design.

The small block Fords have a 3 passage lubrication system, the Cleveland design went backwards with a 2 passage lubrication system. It should have progressed forward with a 4 passage system. Obviously a financial compromise was involved. I don't think the engineers would have designed it this way willingly, the 2 passages must have been agreed upon in committee in order to secure some other aspect in the engine's design. That's just a guess, but it seems plausible.

The manner in which the main oil passages intersect the tappet bores creates large ports in the sides of the tappet bores. Few people comprehend just how severely these large ports impact the Cleveland's lubrication system. They disrupt the flow of oil to the crankshaft, they create extreme leakage at the tappets, they create tappet incompatibility issues, and they give rise to excessive valve train lubrication.

These issues manifest as under-lubricated rod bearings and low hot oil pressure. They are not horsepower related, but more or less rpm related. The lubrication issues are at work, robbing lubrication from the rod bearings, even at low rpm. They worsen as rpm increases. They become so severe above 7000 rpm that bearing failure occurs.

The external oil line between the oil filter passage and the oil pressure port does not resolve the problem. Tappet bore bushings resolve the problem because they eliminate the large ports between the tappet bores and the main oil passages. In fact I like the Cleveland lubrication system better than the small block Ford lubrication system once the bushings are installed in the tappet bores.

My formula for the lubrication system is as follows:

   • Utilize 10W30, 10W40, or 15W40 synthetic motor oil
   • Install a wet sump racing oil pan
   • Install 16 tappet bore bushings (with 0.062-inch orifices)
   • Chamfer the oil holes at the crankshaft journals.
   • Install heavy-duty, fully grooved main bearings; Clevite # MS1010HG or # MS1010VG. If fully grooved bearings (G suffix) aren’t available, improvise by using the upper shells from two sets of standard Clevite # MS1010 main bearings.
   • Install heavy-duty rod bearings; Clevite # CB927.
   • Set the bearing clearances and rod side clearances to promote lubrication:
      a. Main bearing clearance = 0.0025 inch to 0.0030 inch
      b. Connecting rod bearing clearance = 0.0025 inch to 0.0030 inch
      c. Connecting rod side clearance = 0.018 inch to 0.022 inch

Moroso sells a restrictor kit for the Cleveland lubrication system. It contains 4 small restrictors for cam bearings 2 - 5, and a larger restrictor for the left hand oil passage. The larger restrictor has led to the random collapse of hydraulic tappets on the left-hand side of the engine. I wonder if this might explain the collapsed tappet your Pantera's engine recently experienced?

I've explained all of this this a bit more thoroughly in the thread linked below:

https://pantera.infopop.cc/topic/1598208420299384

-G

Last edited by George P
Richard I don't have a hydraulic lifter recommendation I can make at the moment with complete assurance, and I don't want to make one without complete assurance. My old stand-bys from 20 years ago are no longer available.

What I can tell you, you want to find a lifter that is a true "anti-pump-up" design (high bleed rate) that requires adjustable valve train, held together with a nice, sturdy circlip as opposed to the thin wire clips holding most hydraulic lifters together. You want top grade metallurgy, heat treating and surface finishing. You want an internal metering assembly that passes very little oil to the valve gear.

If you were using solid lifters I'd have a recommendation for you because a friend on the Cleveland forum just recently did some phoning around and found a Crower lifter manufactured by Johnson (the manufacturer of the original Boss 351 lifters) using the original Boss 351 style metering assembly, and having the metallurgy, heat treating & finish we're looking for.

I'll ask around and see if I get a "good" reply. In the mean time, if you find anything, share your findings with us.

Crower has a new hydraulic lifter that they advertise as being very close to a solid lifter. But they offer no information on their web site, they just say to phone their tech line. This sounds like one of those limited plunger travel designs. Lunati's lifters may be worth investigating too. One word of caution however, some lifter designs that work fine installed in small block chevys & Windsors don't work well in the Cleveland from the perspective of oil metering.

-G
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