While this chapter isn’t intended to cover a step-by-step rebuild of the 351-ci Cleveland, or 351C, I hope to provide some interesting insight into the history and unique features of this successful engine series. The engine featured here was undergoing a highperformance rebuild at Jordan Automotive Machine and belongs to Lee Lundberg of Mount Laurel, New Jersey.
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At the recommendation of Master Machinist Gil Jordan, the Cleveland received modifications that take advantage of advances in technology since the engine was first assembled, and a combination of aftermarket performance parts that resulted in a stronger, more powerful engine for Lee’s 1970 Torino GT. The Cleveland currently displaces 408 ci thanks to a .030-inch overbore and an aftermarket stroker crankshaft. It has also been converted from a hydraulic flat-tappet camshaft to a more efficient roller style, and features a high-output ignition system. Needless to say, the Cleveland now moves the big Torino down the road with very little effort.
Ford engineers designed the 335 series engines (including the 351C) to power passenger cars and light trucks in the early to mid 1970s. As is usually the case, though high-performance versions were available, certain engineering compromises had to be made in order to fit the engines into the vehicles and also to meet government emission control standards. Those who took the 351C racing soon identified the engine’s performance shortcomings and came up with innovative modifications to increase performance and reliability. While never as popular as the 350-ci Chevrolet small-block V-8, the 351C won enough races and attracted enough attention to garner the aftermarket parts support to compete on the high-banked tracks of NASCAR and drag strips across America.
The hot rod aftermarket industry wasted little time addressing a shortcoming in the 335 oiling system that showed as soon as racers started to really lean on them. It seemed that during high- RPM operation, not enough of the engine’s life-giving oil was feeding the crankshaft main bearings and engine failures were occurring on a regular basis.
To keep more of the oil where it belonged, Moroso Performance developed a restrictor kit. The kit required the small oil holes in the block’s number-2, -3, and -4 main bearing saddles, which feed the camshaft, to be tapped for 1/4-inch by 20 .040 restrictors. The number-5 saddle received restrictors in the holes that feed the camshaft (center hole) and the lifter gallery (right side). The number-1 main bearing oil passages where left unrestricted due to the main and camshaft oil passages crisscrossing at that point. All-out racers using roller tappets were also known to have the lifter bores in the block opened up and solid bushings installed to further limit the amount of oil traveling to the top of the engine.
A Little History
The 335 engine series, of which the 351C is a part, includes features found on Ford’s small-block engines (289/302/ 351W) as well as big-block (429/460) engines. And to make matters even more confusing, Ford built the true small-block 351-ci Windsor during the same time frame as the Cleveland.
The 351-ci Cleveland, named for the Cleveland engine plant, was developed in 1969, first appeared in 1970, and lasted until the 1974 model year. The new engine shared its canted-valve, poly angle combustion-chamber cylinder-head design with the 429/460, while retaining the engine mount locations and bell housing bolt pattern of the small-block. (Canted valves are splayed at an angle, rather than in-line. This improves airflow.) The 351C differs from the 351-ci Windsor in that it has an integral timing cover cast into the cylinder block instead of a stamped cover. The thermostat is located in the block as opposed to the intake manifold as on the 351W, and as a result, coolant was routed from the cylinder heads, through the block, and then into the radiator for improved cooling. The most apparent difference between the two 351s is the canted-valve cylinder heads found on the Cleveland.
Sadly, the performance era at Ford came to an end within one year of the introduction of the 351C engine. Government regulations and the insurance industry put the brakes on high performance offerings from Detroit, and it would be a decade before another exciting car came out of Dearborn. Ford’s last hurrah in the high-performance car market was the Boss 351 Mustang. The Boss 351 was not highly advertised and pretty much slipped beneath the radar, though it was arguably one of the quickest Mustangs in stock form ever built. Available only in 1971, there were just 1,806 Boss 351 Mustangs produced.
The “Boss” in Boss 351 was provided by an honest-to-goodness, purpose-built high-performance version of the 351C engine. Based on the 4-bolt-main Cleveland block, the Boss’s high-nodular iron crankshaft swung a set of connecting rods that had received the hot rod treatment (Magnafluxed and shot-peened) and a set of forged-aluminum pistons. The canted-valve, quench-type cylinder heads with 64.6- to 67.6-cc combustion chambers provided a compression ratio of 11.1:1. A 750-cfm model 4300D Autolite spreadbore 4-barrel carburetor gulped fresh air via a special ram air hood and sat atop an aluminum intake manifold. With a solid-lifter camshaft bumping the valves, the Boss 351-ci produced an honest 330 hp at 5,400 rpm and 370 ft-lbs of torque at 4,000 rpm.
And while the Boss 351 was a stand-alone model of the 1971 Mustang sports roof, the 429-ci Cobra Jet and Super Cobra Jet engines were an option in all Mustang models for the year and these are even more rare than the Boss 351. The 429-ci SCJ/Drag Pack option, while available in the Mustang for 1971, was not offered in the Torino after 1970.
351M and 400
Ford saw a need for an engine that was more efficient than the 385 series, but produced more torque than the existing small-block. The answer was the 400, also referred to as the “400M” for modified, in 1971. Based on the 351C, the 400 block featured a deck height that was 1 inch taller than the Cleveland in order to accommodate its 4.00-inch stroke. The 400 is considered a “square” engine because its bore is also 4.00 inches. The 400 actually displaces 402 ci, giving it the distinction of being Ford’s largest displacement small-block, as well the last pushrod design engine developed by the company. It also boasts the longest stroke of any Ford V-8 engine. With great lowend torque and 20-percent less weight than the 385 series, the 400 was a good compromise engine, and it powered full-size and midsize passenger cars and light trucks until 1982.
335 Series Parts Interchangeability
As with many other Ford engine series, the engineers at Dearborn apparently felt that the waters weren’t quite muddied enough by displacement variety and outwardly similar appearances of the 351C, 400, and 351M engines. So they managed to include some differences that prevent a universal parts interchange across the series. Learning the differences between the three engines is handy, but you’ll still need to learn which parts interchange and which will not. I have already noted the difference in deck height between the 351C and the 400 and 351M so no further discussion is required on that topic. The following is more relevant information.
Cylinder heads: All 335 series engines share the same bore diameter, bore spacing, head bolt size and location, and water jacket passages, so all the heads can be interchanged. The 4V heads have much larger ports, and will have “4V” cast into them.
Intake Manifolds: 2V and 4V engines have dramatically different port and valve sizes. The 2V and 4V intakes will not interchange. Aftermarket intake manufacturers will specify application as long as you know which cylinder heads you have.
Crankshafts: The 400 and 351M have a larger main-bearing journal diameter and thus their cranks will not interchange with the 351C.
Camshaft and timing set: All 335 series engines have the same crankshaft-to-camshaft dimension and block front design, making these parts interchangeable.
Valve lifters, rocker arms, and pushrods: While the valve lifters will interchange, the pushrods will not, due to the different deck height between blocks. The rocker arms on engines utilizing nonadjustable hydraulic-lifter valvetrains will interchange, while those for solid-lifter engines will not. All 335 series rocker arms are 1.73:1 ratio.
Valves: The 351C 2V cylinder head and the 351M share the same valves, but in order to use the larger 351-ci 4V valves, the 351M cylinder head would require modification.
Pistons: While the 351C and the 400 engine share similar compression height (the distance between the wrist pin and the top of the piston), the 400 has a larger wrist pin. The 351M has a taller compression height, so the pistons are not interchangeable with the other engines in the series.
Other: Parts such as the distributor, fuel pump, thermostat housing, oil pump and pan, and water pump are interchangeable throughout the series.
What is Valvetrain Geometry?
To many, the term “valvetrain geometry” conjures up visions of a black art practiced only by those engaged in building all-out competition engines. But in actuality, getting the valvetrain geometry right is important on any overhead-valve engine, since it not only ensures that maximum power is delivered in the most efficient fashion, it also protects vital engine parts against undue The 335 engine series, of which the 351C is a part, includes features found on Ford’s small-block engines (289/302/ 351W) as well as big-block (429/460) engines. And to make matters even more confusing, Ford built the true small-block 351-ci Windsor stresses, wear, and potential failure. In other words, if the valvetrain geometry isn’t right, your engine could lose power and break parts—that should be enough to get you interested even if you don’t plan to go racing.
First let’s discuss the theory behind valvetrain geometry. When the lobe on the camshaft comes up and moves the valve lifter toward the top of its bore, a pivoted lever (the rocker arm) causes the valve to open. The goal is to do this with the least amount of wasted motion by trying to align the midpoint of the pushrod’s travel with the tangent point (rotational center of the rocker arm).
So how do you achieve this? First, we need to discuss the factors that will cause variations in valvetrain geometry. Even though in most cases you would be safe to assume that the factory engineers who designed your engine worked out the geometry, things may well have changed. How, you ask? Processes as seemingly mundane as machining the deck surfaces of the block or cylinder heads can create changes in valvetrain geometry.
But can the average backyard mechanic check valvetrain geometry without a bunch of sophisticated tools? Yes, and the only special tool required is an adjustable-length “checking” pushrod.
The steps are simple. Step one: If your engine is equipped with hydraulic valve lifters, you will first have to install a solid lifter in the lifter bore of the cylinder being checked. Color the tip of the valve using a black marker. Step two: Install the checking pushrod (set to the length of the OE pushrod) and a rocker arm. Set the rocker arm to zero lash. Step three: Rotate the crankshaft in its normal direction of rotation through two or three complete revolutions. Now remove the rocker arm and look at the pattern left by the tip of the rocker arm on the valve.
If the geometry is correct, the pattern should be narrow and centered on the tip of the valve. If the pushrod is too long, the pattern will be wide and off center toward the exhaust (outside) of the valve tip. If the pushrod is too short, the pattern will be toward the intake side of the head. Correcting this misalignment is a matter of adjusting your checking pushrod (either longer or shorter according to the pattern on the valve tip) and repeating the process until you get the pattern right.
From this point, you have the option of requesting that your machine shop accurately measure the length of your checking pushrod using specialized tools, or you can pack the measuring pushrod off to your chosen aftermarket pushrod supplier and purchase a set of rods made to this length. Either way, when your engine goes back together, you can be confident the valvetrain is geometry correct.
351C Performance Cylinder Heads
For an engine series with a relatively short life span, the 351C has done more than its share to make a mark in the world of motorsports competition. Along the way, it has garnered enough fans to justify the performance aftermarket developing of parts to keep them racing.
There was a time when the 1970 to 1971 4V 68-cc closed chamber OE cylinder heads, with their 2.19-inch intake and 1.71- inch exhaust valves, were considered the hot setup, as the Boss 351 head was just too rare for general use.
With all their strong points, the 4V Cleveland head had one glaring drawback that at first glance does not appear as such. These heads have intake ports that are large enough to be called “cavernous.” While large intake ports are great in the upper RPM range, they aren’t so great down low, providing a narrow powerband that is detrimental for street performance.
The last closed-chamber Cleveland cylinder heads were cast in 1972, and while they shared valve sizes with the early castings, the combustion chambers grew to 75.4 cc. The future for 351C looked bleak.
But then hope came from the most unlikely of places and it would not be from the aftermarket. Our friends down under found the design of the 335 series Ford engine much to their liking. In true Aussie fashion, they added a little of their own magic to the combination, reducing the displacement to 302 ci, which in turn called for a redesigned cylinder head. It did not take long before the new cylinder head was discovered here and became coveted by American performance enthusiasts, who christened it the “Australian Cleveland head.”
The Australian Cleveland cylinder head is a new combination of a number of characteristics found in different 335 series heads. The Australians combined the smaller 2V-size intake port with 58-cc closed combustion chambers filled with the larger 4V-sized valves. The Aussie head became the ultimate street performance cylinder head available for the Cleveland at the time.
Since that time the Australia based aftermarket company AFD has developed aluminum cylinder heads for the 351C in both 2V and 4V intake port configurations. The AFD 4V head features 57- to 64-cc closed combustion chambers with 2.19- inch intake and 1.71-inch exhaust valves. These heads flow 298 cfm on the intake port and 205 cfm on the exhaust side at .500 inch of valve lift. The 2V version of the head has 60-cc chambers, 2.05-inch intake and 1.65-inch exhaust valves and delivers 290 cfm on the intake and 217 cfm on the exhaust side at .500 inch of lift.
Ford eventually cast its own high-performance version of the 351C head in aluminum (PN M-6049-A3) but these heads have since become unavailable.
Blue Thunder, a long-time producer of cylinder heads for Ford products, has an all-out racing version of the Cleveland head patterned after the current style of head used on Ford NASCAR engines. This head fits both Cleveland and Windsor cylinder blocks. Available with valve sizes from 2.02 to 2.20 inches on the intake and 1.60 to 1.70 inch on the exhaust, the Blue Thunder head also boasts the Yates exhaust port, named for its designer and legendary Ford racing-engine builder Robert Yates. Since these heads are designed for use in racing competition only the, flow numbers are all listed at .700 inch of valve lift and higher. These heads would not be compatible with an engine built for street use.
Edelbrock, who started casting heads for Fords over five decades ago, is also now making some great Cleveland heads. The new Edelbrock head (part number 61629) sports a tight 60-cc combustion chamber fed by 2.05-inch intake and 1.60- inch exhaust valves. Flow numbers at .500-inch lift—267.9 cfm on the intake and 160.8 cfm on the exhaust—are very impressive for a head primarily designed for high-performance street use. Edelbrock has also developed a version of its successful Air Gap intake manifold to go along with the new heads. Modified Mustangs and Fords magazine reports 450+ hp plus Dynamometer readings from a Cleveland using the new heads and intake combination.
CHI, or Cylinder Head Innovations, is the latest aftermarket company to jump in with an aluminum 351C cylinder head. CHI makes a variety of heads for the Cleveland engine, some of which are winning awards such as the Engine Masters Challenge.
If you look closely at the engines being used in NASCAR competition by the Ford teams, you can’t help but note the Cleveland-style cylinder head on top of the Ford Racing Windsor block. Even Chevrolet has adopted a canted-valve cylinder head with port spacing that looks suspiciously similar to the Cleveland for its NASCAR engine. As they say, imitation is the sincerest form of flattery.
With continued interest from competitors and continued parts development through the aftermarket, I hope to see the Cleveland bad boy around for quite a while.
Written by Charles R. Morris and Republished with Permission of CarTech Inc
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