We’ve discussed the Clevor — a portmanteau of “Cleveland” and “Windsor” — previously, and its most well-known factory variant, the BOSS 302. Originally developed for Trans-Am road racing, Blue Oval engineers decided to take the BOSS 351’s cylinder heads and fit them to the 302 Windsor short block, rather than trying to destroke the 351C to fit the series’ limited displacement rules.

Of course, enthusiasts caught on to this, and in a time before high-flowing Windsor heads were an off-the-shelf affair, Clevor hybrids made a lot of sense to get big cylinder head flow with a standard small-block Ford short-block. We actually have a test coming soon, where we pitted modern aluminum Windsor heads against modern aluminum Cleveland heads on the same short-block to see the performance difference. But that is a totally different article.

For this article, we head back to our friend Jeff Huneycutt at The Horsepower Monster. Huneycutt has a friend with a Cleveland engine in need of a rebuild, but is already at the maximum bore size. So, rather than go hunt down a usable 351C block, Huneycutt decided to try his hand at building a Clevor himself. Taking the high-flow canted-valve Cleveland heads and putting them onto the Ford Racing 9.5-inch deck Windsor block should give his friend the best of both worlds.

The Windsor Bottom End

The 351C has a 9.2-inch deck which is a lot closer to the 9.5-inch deck-height of a 351 Windsor as opposed to the 8.2-inch deck height of the original Clevor, the BOSS 302. Coming out of an old Ford Motorsport 351 circle-track crate engine, the block has never actually seen combustion. It’s a two-bolt-main, iron block, with plenty of room for a big stroke and thick bores to be able to add piston diameter while maintaining strength. Both will be needed for the planned 408-cube build.

The short-block of a Clevor is a standard Windsor unit, with the exception of the coolant passage at the lower right on cylinders 2, 3, and 4. They are present on aftermarket Windsor blocks, but will need to be drilled if you’re using an OEM 351W block.

The block’s bores were opened up to 4.030 inches by Automotive Specialists, which is the entirety of the machine work completed on the block. Into the mains went an Eagle 4340 forged 4.00-inch-stroke crankshaft that was balanced by grinding the counterweights instead of the typical drilling of holes. Hanging onto the crankshaft is a set of Eagle 6.250-inch forged H-Beam connecting rods.

The pistons are slightly unique, in that they are not unique. The block would have easily handled a 4.125-inch bore, but finding a set of off-the-shelf 4.125-inch bore Cleveland pistons with all the modern accoutrements proved to be a challenge, while JE Pistons has a set of 4.030-bore pistons that fit the bill on the shelf, in the company’s SRP lineup. So, 4.030 inches it was. The 16cc dish keeps compression in check, if not a bit on the low side, at 9.7:1.

Covering the bottom end is a Milodon oil pan and pickup tube. Huneycutt says that of all the pans and oil he’s used, the Milodon ones have always fit the best. I’m sure the aesthetics of Milodon’s gold-zinc don’t hurt, either. Huneycutt chose an eight-quart pan with a deep sump, but opted not to run a windage tray, since it mounts using main studs, and the block was align-bored with main bolts. A Milodon mechanical water pump was also used.

The largest difference in the Cleveland heads is the canted valves. The valve angles are much more advantageous than the Windsor’s inline 20-degree angle.

The Star Of The Show – The Cleveland Top End

The most obvious difference between the Cleveland and Windsor cylinder heads is the valve angles. The Windsor heads have a 20-degree inline valve angle, while the Cleveland heads have canted valves. That is, the intake and exhaust valves are at different angles, canted away from one another, for better flow. The Cleveland heads also have much larger ports on both the intake and exhaust sides.

While the stock heads were decent performers back in the ‘70s the pinnacle of Clevor performance are modern Cleveland heads. For that, Huneycutt used a set of Trick Flow 225 CNC-ported Cleveland heads. Big CNC intake ports, raised CNC exhaust ports, and large canted valves, with a modern combustion chamber. The Trick Flow heads come assembled with titanium retainers and valve springs spec’d for up to .650 inch of lift. They are held in place with a set of half-inch ARP cylinder head bolts

Cleveland heads on a Windsor block is about 90 percent bolt-on. The 10 percent though, takes a little care. The first step is to block off the 3/4-inch coolant passages unique to the Cleveland design. That is easily accomplished with an NPT plug set, because Trick Flow threads the passages out of the box, knowing that Clevors are a thing.

Then, to replace the blocked-off passages, you must drill a new coolant passage in the head. Once again, Trick Flow knows that Clevors are a thing, so they actually dimple the location in the head where you need to drill a 1/2-inch hole. If you’re using an OEM Windsor block, you’ll need to drill a few holes in the deck of your block to match up as well, but since Huneycutt is using an aftermarket block, those passages are already there, as they are in most aftermarket Windsor engine blocks.

The camshaft is a Comp Cams hydraulic roller unit with .644 inch of lift on both the intake and exhaust, with 231 degrees of duration at .050 inch of lift on the intake and 239 degrees on the exhaust, with a 100-degree lobe-separation angle. Riding on those lobes are a set of Comp Evolution link-bar hydraulic roller lifters.

Different length pushrods are required for the Cleveland heads, 8.300 inches long on the intake and 8.400 inches for the exhaust. Both are 5/16-inch-diameter, .080-inch wall-thickness pushrods. Translating cam motion into valve motion is a set of Comp Pro-Magnum rocker arms. They are a stud-mounted rocker featuring a steel body and hardened roller tip in a 1.73:1 ratio.

Induction for this engine combination is deceptively simple. The dual-plane intake is topped by a Holley Sniper Stealth EFI system, and will provide all the air and fuel the combination needs.

Topping off the combination is an Edelbrock Clevor-specific dual-plane intake manifold. Geometry tells us that a 9.2-inch Cleveland deck height and a 9.5-inch Windsor deck height are going to create some alignment issues, and that’s what the Edelbrock intake manifold takes into account. However, two holes needed to be drilled for coolant flow in the intake flanges. To provide fuel, Huneycutt went with a Holley Sniper Stealth EFI system that fits the Edelbrock intake’s 4150 flange, but provides all the convenience of modern EFI.

After a quick break-in process and getting the Sniper’s self-learning up and running, Jeff Dorton pushed the throttle on the dyno forward for its first full pulls in anger. Huneycutt’s goal in this project was street-usable torque, and boy did he accomplish that goal with 526.5 lb-ft at 4,300 rpm. Horsepower just kept climbing throughout the pull as well, peaking at the end of the pull, showing 546.6 horsepower at 6,200 rpm. Not bad at all for a 408 cubic-inch Clevor hybrid with mild compression and a baby cam, proving that the Blue Oval hybrid still has a place in the modern age.

This is a mighty fine looking graph for a mild 408 that will live in a truck to be driven on the street. 546.6 horsepower at 6,200 rpm and 526.5 lb-ft of torque at 4,300 rpm will make for plenty of grunt.