Clevor: Cleveland Heads on a Windsor Block

A Clevor is a 351 Windsor short block wearing Cleveland cylinder heads. The name is a portmanteau and the idea is simple: the Windsor block is common, cheap, and stroker-friendly; the Cleveland head is the better breather. Put them together and you get most of what makes a Cleveland special without spending a season hunting a good Cleveland block.

It works. It is also not a bolt-on, and the people who get burned are the ones who found out about the coolant routing after the heads were already on.

Why anybody does this

Blocks. Good 351C blocks are getting scarce and expensive, and the ones that surface often need sleeves. The 351W was built from 1969 into the mid-1990s in enormous numbers and is still cheap.

Cubic inches. The Windsor block's taller deck — 9.503 inches versus the Cleveland's 9.206 — and its main size make stroking straightforward. 393 and 408 combinations are ordinary parts-store builds on a Windsor. A Cleveland stroker is a more specialized project.

Airflow. The Cleveland's canted-valve head, with its big valves and straight shot at the port, out-breathes a factory Windsor head by a wide margin. That is the whole reason to bother.

What actually has to change

Coolant routing — the big one

This is the modification that defines the swap. The two engines move coolant differently:

• On a Windsor, coolant leaves the heads at the front and crosses over through the intake manifold to the thermostat.
• On a Cleveland, the crossover is in the front of the block, and the heads do not route coolant through the manifold the same way.

Bolt a Cleveland head to a Windsor block unmodified and you get passages that do not line up and a cooling system that will not circulate correctly. The fix is to block the Cleveland head's front coolant passages and route coolant the Windsor way, using a head gasket designed for the application and, on most builds, drilling the heads to open a path to the deck. Every established Clevor recipe handles this; the mistake is assuming a standard Cleveland or Windsor gasket will sort it out.

The intake manifold

Because the Windsor deck is nearly three-tenths taller and the head is sitting at a different height and angle relative to the valley, a stock Cleveland intake will not fit. You need a Clevor-specific manifold — the port shape of a Cleveland head with the mounting geometry of a Windsor block. These exist from several manufacturers; budget for one, and confirm it matches your specific head's port location, especially if you are running an aftermarket head with a raised port.

Pistons

The Cleveland's canted valves sit at different angles than a Windsor's. Windsor pistons have the wrong valve reliefs. You need pistons cut for Cleveland head geometry, which is a normal catalog item from the major piston makers — just make sure the order says Clevor, not 351W.

Compression is worth pausing on here. With a 60-62cc aftermarket Cleveland chamber and a flat-top piston on a 9.503-inch deck, you can land anywhere from the high nines to over 11:1 depending on stroke and gasket. Work it out on paper first, and set quench deliberately at .035–.045 inch.

Heads

Factory Cleveland iron will work on a Clevor, and plenty of people have done it with 2V castings. But the aftermarket has made this easy: Trick Flow's PowerPort Cleveland 195 and 225 heads are cataloged for 351C, 351M/400 and Clevor in the same casting family. Buying a head that lists Clevor as a supported application takes most of the guesswork out of the coolant and intake questions, because the supporting parts exist as a system.

Everything else

• Head bolts/studs — Cleveland pattern, and studs are worth the money on a high-compression build.
• Valvetrain — Cleveland rocker geometry, pushrod length checked with a checking pushrod, not guessed.
• Headers — Cleveland exhaust port, Windsor block. Confirm the header is sold as Clevor.
• Distributor and oil pump drive — Windsor, since the block is a Windsor.

When Clevor is the wrong answer

If you already own a good 351C block, build the Cleveland. The hybrid exists to solve a block-availability problem you do not have, and you will spend the savings on Clevor-specific parts.

If you want a numbers-correct or period-correct car, obviously not.

And if your goal is torque in a heavy street car rather than top-end airflow, a well-built Windsor with a good aftermarket Windsor head will get you there for less money and less fabrication. Clevor makes sense when you want Cleveland breathing and Cleveland rpm on a budget block — not as a default.

Model it before you commit

The simulator handles Cleveland heads on Cleveland cubes; for a Clevor, build the displacement you are planning (393, 408) with the Cleveland head and intake you intend to run and the numbers will track closely, since the head and cam are doing the work. Then price the coolant modification, the Clevor intake and the pistons before you decide it is cheaper than a Cleveland block.

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