Ford’s 351ci Cleveland middle block entered production more than three decades ago in the fall of 1969. Its production and service life was all too brief, unfortunately, lasting through the 1974 model year. Ford’s decision to terminate 351C production was rooted in scaling down production costs. After the 351C was introduced in 1970, Ford was already at work on an FE Series bigblock replacement called the 400M – the tall-deck Cleveland block displacing 400ci that was introduced for 1972. The 400M looks a lot like its smaller 351C counterpart except for the taller deck and wider profile that come from the 4.00- inch stroke inside. Instead of the 351C’s small-block bellhousing bolt pattern, the 400M has the 429/460’s big-block pattern, which makes it compatible only with 385-series big-block transmissions, such as the C6 automatic.
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The 400M replaced the FE Series 390ci big block, which was common in full-sized Fords and Mercurys. Later on in 1977, the 400M design would find its way into F-Series trucks as well. In 1975, Ford took the 400M and destroked it to 3.50-inches to achieve the 351M, an underpowered, overweight version of the 351C it replaced. This means the 351M isn’t just a 351C with a new designation. It means the 351M is 351ci inside a 400M block, which is considerably heavier than the 351C block. The 351M and 400M have the 351C-2V head, with open chambers and smaller ports.
If you’re going to build an M block, bore and stroke this block to more than 400ci for a wealth of good torque. Top the block with 351C Aussie heads, with wedge chambers and the 351C-2V ports for optimum torque. A stroked 400M isn’t for performance use, but more for good power in a tow vehicle. It is not an engine you would want to spin to 7,500 rpm in a road-race vehicle or drag car.
Our focus here isn’t the 351/400M, but the 351C and what can be done with this short-lived Ford powerhouse. Most of us will never know what Ford engineers were thinking when the 351C was developed. Its huge ports mirror the 429/460ci big-block’s. Yet, there isn’t the displacement in the 351C witnessed with the high-displacement fat-blocks. The 351C-4V head is long on potential if you’re planning a 7,500-rpm engine. Those huge intake ports allow an abundance of air and fuel to pass. But these ports are useful only at high revs, where enough velocity can be developed to feed the bores and provide cylinder pressure.
The 351C-4V is virtually the same head casting used on top of the BOSS 302 small block produced in 1969 and 1970. Ford engineers borrowed this head for the BOSS 302 to make the most of the high-revving 302ci small-block’s potential. This approach worked with great success in SCCA Trans Am competition. The 351C-4V head has huge 2.50 x 1.75-inch intake ports. On the exhaust side, 2.00 x 1.74-inch. Valve sizing runs 2.19-inch intake and 1.71-inch exhaust. These dimensions are overwhelming in a street engine. What they mean for you is poor low-end torque, short on the grunt factor. Large ports like these don’t give you the hole-shot advantage on the street. On the drag strip, they come on strong at high revs. Ditto for the race course.
Poor low-end torque has an unpleasant feel. Lean on the throttle coming out of the hole and the large-port Cleveland or BOSS 302 falls right on its face. It doesn’t make torque down there. Carry the revs skyward and these ports begin to go to work. But even in the most powerful of 351C engines, the potential of these ports is never realized. They need 7,000 rpm and higher to be working at all with a displacement of 351ci.
The best way to make the most of the 351C-4V head is to stroke your 351C to utilize this engine’s displacement potential. Both Coast High Performance and Speed-O-Motive offer stroker kits for the 351C middle block. These stroker kits are available in price ranges to meet all budgets. If you want a high-revving screamer, there are highend kits available for the 351C that will allow you to make the most of this legendary performer. If you are limited by budget, you don’t have to be limited on power. You can pump as much as 408ci into the 351C for under $2,000. Because the 351C makes a lot of power in stock displacement form, it only gets better with more displacement. With 377ci inside, the 351C makes even more power. But with 408ci, the displacement of a big block, the 351C comes on very strong. You may also bore the 351C to 4.040-inches for a pinch more power. We discourage taking the Cleveland block to 4.060-inches.
The key to making real stroker power with the 351C is to stroke as much displacement as possible into its bores in order to make the most of its large-port heads. This means you need a stroker kit that will allow you to spin it to at least 6,000 rpm for best results. If you want to spin the Cleveland even higher, we suggest a 377ci stroker kit with H-beam rods and a steel crankshaft in the interest of staying well within the limits of the Cleveland’s design. Based on what we’ve been told by seasoned engine builders, the 408ci Cleveland stroker approach pushes this engine to the limits of its intended design, which puts the package more at risk if we try spin it to 7,500 rpm. Closely examine each engine kit to determine limits and approach your build-up from there.
While you are planning your 351C stroker build, close attention to camshaft selection must be practiced, which is where the folks at Comp Cams come in. Comp Cams is customer friendly, and eager to help you with your camshaft and valvetrain selection. Comp Cams will sit down with you on the telephone and get you pointed in the right direction on your camshaft and valvetrain. Always order your cam and valvetrain as a cohesive package from the same manufacturer.
Comp Cams, for example, tests the daylights out of its products with real dyno and road testing. The great talent within these companies discovers what works on the street, just like the rest of us. Comp Cams, for example, refines its product this way. When you stuff a Comp Cams bumpstick inside your block, you’re getting the result of extensive testing and refinement, making it an excellent value for your hardearned dollars.
Camshaft selection for a 351C stroker depends on how you plan on using the engine. For one thing, we suggest a good roller hydraulic camshaft just for starters. Then, you need to look at valve timing events closely. Cam-timing events need to make the most of the displacement, bore, and stroke that you have selected. These elements also have to capitalize on the cylinder head design as well. Because we’re dealing with two cylinder head designs with the 351C, this becomes easier.
We’ve addressed the 351C-4V head at length. Because the 4V head has such huge ports, we have to spin the 351C high to make the most of these woefully over-engineered castings. The thing is, not all 351C projects need to spin to 6,500 rpm. You may be building a 351C for a pick-up or a van where you need pulling power. This means you need only rev to 5,500 rpm to get the job done.
So what do you do when cylinder heads yield way more potential than your 351C will ever realize? There are two answers for this one. One is the 351C-2V head with smaller sized ports and open chambers. The other is Australian 302C and 351C heads, which have the smaller wedge chambers we find with the U.S. 351C-4V head, coupled with the smaller 351C-2V ports. The 351C-2V head has 2.02 x 1.65-inch intake ports, followed by 1.84 x 1.38-inch exhaust ports. Stopcocks are sized at 2.04-inch intake and 1.67-inch exhaust.
The Aussie 351C head is your best choice because it employs the Cleveland’s best features – adequately sized ports and valves, coupled with the wedge chambers. We like the Aussie head because its wedge chamber gives us the best result. The open, lower compression chamber we find with U.S. 351C-2V heads tends to cause detonation, regardless of how you tune the engine. One theory is that the 351C-2V head sets up two flame fronts that collide, causing the detonation we hear as pinging under acceleration. We don’t experience this with 351C-4V heads or the 351C Aussie head. This tells us something positive about this cozy wedge chamber.
Regardless of what type of 351C/351M/400M cylinder head type you’re going to use, you need to fit yours with pushrod guide plates and screw-in, adjustable studs. This enables you to adjust your valvetrain accordingly.
The aftermarket offers us very few types of intake manifolds for the 351C.
Edelbrock brings us the Perfomer series manifolds for the 2V and 4V engines. The Performer manifolds are two-plane pieces designed to deliver good low-end torque. These manifolds also work quite well at high RPM. There is also the Edelbrock Torker single-plane manifold, which is more appropriate for drag and road racing applications where the engine does its best work at high revs only.
Swap meets offer us a wealth of older 351C aftermarket manifold designs from Offenhauser, Edelbrock, Weiand, Holman/Moody, Ford, and others. Good rule of thumb is to opt for the dual-plane types for street use and single-plane for racing.
Building the Speed-O-Motive 408ci Cleveland
Seems we’ve forgotten the legendary 351 Cleveland middle block in the 30 years since production ended in 1974. But, this engine stood the drag racing world on its ear three decades ago with its blistering, coyote-nasty performance. Jack Roush understood this with the Tijuana Taxi Maverick sedan that could crack a solid 8-second quarter mile pass. Ford fans loved the Tijuana Taxi for its extraordinary power and speed. That speed was achieved with the 351C.
What has hurt the 351C in performance circles has been casting availability. This engine was produced for the four years spanning 1970 through 1974, which greatly limits available parts for project engines. But all is not lost for the 351C. There are still cores laying around, waiting to be discovered. There is also talk of the aftermarket getting involved on 351C block and heads for those who still believe in this engine’s legendary performance.
Few manufacturers believe in the 351C more than Speed-O-Motive, which has been producing stroker kits for Fords since 1946. Speed-O-Motive has a couple of stroker kits for the 351C middle weight, displacing 377 and 408ci. Because the 351C-4V head has huge ports that don’t really serve us very well on the street at low revs, the greatest favor we can do these tunnels is huff more air and fuel through them. Speed-O-Motive’s very affordable 408ci stroker kit will get the job done with room to spare.
We’re going to show you the Speed-O-Motive 408ci stroker kit and stuff it inside a 1970 351C block. Then, we’re going to tell you what kind of power you can expect from this torque-making powerhouse.
Written by George Reid and Posted with Permission of CarTechBooks