OK, we admit it. We haven't been giving the 351 Cleveland enough ink lately. Seems everyone is building the venerable 289/302/351W small-block, which our readers love because they're plentiful and easy to build. That makes it easy for us--perhaps a little too easy.
Ford's legendary 351C middle-block was a back-door surprise for 1970. In 1969, Ford introduced the raised-deck 351 small-block we came to know as the Windsor. It looked similar to the 289/302, but it was a pinch wider, a hair taller, long on torque, and ready to make unrealized power. Then, scarcely a year into production, the 351W had company: the more powerful close cousin with the same displacement in the form of the 351 Cleveland. It's often been asked, why the same displacement from a different engine family? There have been a lot of theories, but so far no concrete answers from anyone who was there to see it unfold firsthand. We'll kick around some solid theories later in this article.
The 351W was little more than a raised-deck 289/302ci V-8 with the same 4.000-inch bore, but half an inch more stroke than the 302. It also had similar cylinder-head castings with slightly larger valves and ports. The 351C's 4.000-inch bore and a 3.50-inch stroke was dimensionally the same as the 351W, but it differed in block design and large-port, poly-angle-valve heads. The large-port heads were designed to flow better at high rpm, allowing the 351 middle-block to make extraordinary horsepower and torque on the racetrack. On the street, the 351C wasn't the powerhouse it was on the track because the oversized ports didn't yield the velocity at low rpm necessary to make good torque. This was certainly true with the 351C-4V and Boss 351 engines. In 351C-2V applications, low-end torque was improved, thanks to smaller valves and ports. But the 2V heads suffered from combustion-chamber shortcomings that caused excessive spark knock and reduced compression.
When building a 351C, it's a good idea to know how to amass the right parts to make the most of your buildup. We're going to show you how to coax more horsepower and torque from a 351C without having to sell the farm.
Crate engines from Speed-O-Motive...
Crate engines from Speed-O-Motive make the going easier. Here's a 408C stroker crate short-block ready for shipment. Speed-O-Motive delivers your crate engine in a nice container like this for solid protection.
This is Speed-O-Motive's 408C...
This is Speed-O-Motive's 408C stroker kit for the 351C engine with a 4.000-inch stroke, 6.000-inch Chevrolet rods, forged dished pistons, and a custom nodular iron crank--all precision balanced for assembly.
When we witnessed this build...
When we witnessed this build at Speed-O-Motive, the customer's budget was limited, so this engine didn't reach its potential. The buyer opted for an aggressive flat-tappet Comp Cams 260H High Energy flat-tappet camshaft, but we're convinced more power could have been had from a roller hydraulic camshaft, which is more expensive.
Three basic castings are available...
Three basic castings are available for the 351C: the 4V head shown, the 2V head (not shown) with smaller ports and valves with open chambers, and the more desirable Australian Cleveland head that offers the best of all worlds.
The Aussie head has the closed...
The Aussie head has the closed wedge chambers (4V head) with the smaller ports and valves (2V head) for improved torque. The 4V head shown performs much better when you're huffing 408 ci through those ports for improved low and midrange torque. You're also getting the mechanical advantage of a 4.000-inch stroke and the dwell time from longer 6.000-inch Chevy rods.
Our platform is a '70-vintage...
Our platform is a '70-vintage 351C casting (D0AE) that has been bored .030 inch. The main saddles have been checked and line-honed to keep the bearings secure. As you can see, the bores have been notched to clear the 408 stroker rod bolts. Oiling system mods are simple: one restrictor between the No. 1 main journal and the No. 1 cam bearing. This reduces flow to the cam bearings and increases flow to the mains where it's needed most.
Formula For Success
Engine building isn't always just about engine building; it's also about choosing the right parts. Building a healthy street Cleveland involves choosing the right heads and induction system, which is key with the 351C. Choose a single-plane manifold and 4V heads with a 351-inch bottom end, and you can forget low-end torque. A single-plane manifold with 4V heads makes its power at high rpm. And that means peak torque around 6,000 rpm, not at 3,500 rpm where you need it most on the street.
The 351C-2V head is more appropriate for street use because it has smaller ports and valves, which moves peak torque down where we need it most: at 3,500 rpm. Choosing the right camshaft profile and dual-plane intake manifold improves driveability tenfold. Torque comes on crispy and strong as the engine spins through 2,500-4,000 rpm. The downside to the common U.S.-built 351C-2V head is its wide-mouth open chamber. You get good quench with this chamber, but lousy dynamics because it tends to create two flame fronts under hard acceleration, which causes spark knock (pinging).
The best Cleveland head on the planet is the Australian 351C, with the best combination of ports and chambers: the 351-4V wedge chamber and the 351C-2V ports for better low and midrange torque. PowerHeads is your source for the Aussie Cleveland heads, which are supplied ported and fitted with hardened exhaust valve seats. It's the perfect Cleveland street head.
Speed-O-Motive builds its 351C much the same way it does small-block 289/302s. Oil galleries get a workout where necessary. Oil return flow is improved to ensure sufficient oil in the pan. Press-in oil gallery plugs are tossed in favor of screw-in plugs.
Screw-in oil gallery plugs...
Screw-in oil gallery plugs are installed in front of the block for improved oiling system security.
Because Speed-O-Motive hones...
Because Speed-O-Motive hones the main saddles, main bearing security is improved. We're running a nodular-iron crank, so we're using regular street bearings. Use race bearings only with a steel crank.
Rear main seals tend to be...
Rear main seals tend to be chronic leakers with small-block Fords, but it doesn't have to be that way. First, make sure the rope-seal retainer pin is removed.
Line the seal grooves with...
Line the seal grooves with a good silicone sealer and seat the rear-main seal halves. Then, stagger the seal gaps away from the main-cap gaps to reduce the risk of leakage. Use sealer between the cap and block.
We like the way Speed-O-Motive...
We like the way Speed-O-Motive massages its crankshafts, with nice chamfer work at the oil openings and nice radius work at the journals.
Speed-O-Motive checks bearing...
Speed-O-Motive checks bearing clearances two ways: by measuring the journals and bearings...
...then using Plastigage to...
...then using Plastigage to confirm the measurements. In this case, we have .002 inch of clearance.
Before Speed-O-Motive installs...
Before Speed-O-Motive installs the crank, it applies sealer between the seal and groove, and between the main cap and block. Engine assembly lube goes on the main bearings to ensure good lubrication on startup.
We're running a flat-tappet...
We're running a flat-tappet hydraulic camshaft in this application, which gets us 414 hp and 446 lb-ft of torque. A roller cam with Aussie heads would get us closer to 500 hp and in excess of 500 lb-ft of torque.
Piston-ring end gaps are important...
Piston-ring end gaps are important to power. If you run the gap too close, there will be too much friction when things get hot. If you run it too loose, you wind up with blow-by. You need an optimum balance between a tight end gap and a loose one to use as much of the thermal energy as possible without creating too much friction. Check with your ring manufacturer because each is different.
The common belief is that...
The common belief is that the two top rings are compression rings, but this is only half true. The top ring is a true compression ring for cylinder sealing, and the second is a compression ring and an oil-control ring designed to keep oil out of the combustion chamber. Note the dished forged pistons to control compression. Because we've added a stroke to the 351C's bores, compression is increased. Dishing the pistons gets it back where it belongs at around 10.5:1.
Did you know the oil rings...
Did you know the oil rings are there to carry oil down the cylinder wall? Bench-racing logic has it backwards. Most believe the oil rings carry oil up the cylinder wall. Oil rings simply control oil patterns between the piston and cylinder wall.
These 6.000-inch Chevy rods...
These 6.000-inch Chevy rods get 3/8-inch ARP bolts for strength. Side clearances have been checked. Ditto for crankshaft endplay.
Conventional flat-tappet hydraulics...
Conventional flat-tappet hydraulics are installed for the flat-tappet cam. Notice the painted valley for improved oil return flow.
Here's a common 351C mistake....
Here's a common 351C mistake. Someone has removed the brass coolant-flow restrictor, which every 351C/351M/400M must have.
Here's where a 351C differs...
Here's where a 351C differs from the garden-variety small-block Ford. Coolant never enters the intake manifold because the 351C has a dry manifold. At the upper righthand corner of the 351C head gasket is a coolant passage that carries coolant to the thermostat. The same is true on the other side. Be careful because you can install the 351C head gasket backwards and experience overheating. The little square passages go at the front--and "front" means front.
This Speed-O-Motive 408C is...
This Speed-O-Motive 408C is getting 351C-4V heads for abundant airflow. On the dyno, it makes 414 hp at 5,500 rpm and 446 lb-ft of torque at 4,500 rpm. The downside is, torque doesn't peak until 4,500 rpm, making even a 408-inch stroker pretty sluggish at low rpm. If you're going racing on Saturday nights, this is a nice package. For cruising, it lacks. Torque begins to come on strong at 3,000 rpm, with a broad torque curve beginning at 3,000 rpm and winding up at 5,500.
Because the 351C is a wet...
Because the 351C is a wet deck, high-temp sealer is necessary on cylinder-head-bolt threads. Ditto for screw-in rocker-arm studs.
Hydraulic lifters are adjusted...
Hydraulic lifters are adjusted the same way as on the 289/302/351W. Set the valve lash at the lobe's base circle (valve closed), tighten the rocker adjustment to snug, then tighten the nut half a turn. These are Comp Cams Pro Magnum roller-tip rocker arms for reduced friction.
This is the Edelbrock Torker...
This is the Edelbrock Torker 351C, good for high revs with torque coming on strong around 4,000 rpm. For street use and cruising, you need a dual-plane manifold and a Barry Grant Street Demon carburetor. With 408 ci, a 750-cfm carburetor works best.
The Aussie Connection: PowerHeads
PowerHeads can set you up with Australian 351C heads that are ported and steel seated for optimum performance. The Aussie Cleveland head has the 351C-4V wedge chamber, coupled with "right-sized" ports for great low and midrange torque resulting in good street performance. The 351C-4V chamber offers good quench, coupled with a tight wedge design for reduced detonation. A little bit of work around the intake valves improve flow. PowerHeads works the ports and bowls, which will help your 351C make more horsepower and torque. You can get into these guys for under $1,000.
Cleveland: The Knudsen Connection
We have long accepted the 351C as a small-block Ford, although its weight and size tend to make it more a middle-block--a small-block with larger heads that makes big-block power. However, the 351C's basic architecture says "small-block Ford" with identical bore spacing and size.
Where the 351C block differs is the wraparound iron timing-set compartment, steel timing cover, and a 12/6-o'clock fuel-pump bolt pattern. At first glance, the front of the 351C/351M/400M block resembles the Oldsmobile Rocket V-8s of the era. All had a wraparound timing compartment with a steel cover and 12/6-o'clock fuel-pump bolt pattern.
Here's a loose theory we wish we could confirm. Did Bunkie Knudsen and the engineering people he brought over from GM spearhead the 351C? Semon E. "Bunkie" Knudsen was hired away from GM's Pontiac Division by Henry Ford II in 1967-1968 to run Ford Motor Company. Key events in Ford history were the result of Bunkie's involvement at Ford: the '69-'70 Boss 302 and 429, '71 Boss 351, '69 Talladega/Spoiler II, bolt-on front fascias, and the pucker-mouth '71 Thunderbird and '72 Torino with the Knudsen "Pontiac" nose.
Did Knudsen influence Ford history underhood? Is his influence the reason there were two 351ci engines? We can envision a huge political struggle between Knudsen's people and Ford's people at the time: Knudsen's people for a revised 351ci engine (ultimately called "Cleveland") and Ford's people in favor of staying with the 351W.
When you study the 351C's architecture with its Oldsmobile-like iron block and big-block Chevrolet-like canted-valve heads with huge ports, could Knudsen's influence have been far behind? What's more, take a good look at the 385-series big-block Fords--the 429 and 460. Note the wide canted-valve heads and block design. Then, study the 396/402/427/454ci big-block Chevrolets. Note the similarities in the two designs. Aside from the front-mounted distributor, the Ford big-block is virtually identical to the big Chevy. Can anyone out there help us solve this mystery?