When it comes to the small-block Ford engine architecture there are two main players. The Windsor, known for its robust reliability and inexpensive components, and the Cleveland, whose canted valves and massive ports from the factory have been said to regularly swallow golf balls. Beyond their cylinder heads, they aren’t incredibly different, at least at a functional level. Of course, in our world, it’s no surprise that people have taken the best of both worlds and combined them.
In the past, there have been several engine builds where the Ford Windsor has been outfitted with a set of Cleveland heads. The modifications to fit a set of Cleveland heads is not that intensive, but require time and effort nonetheless. These engine platforms are often referred to as a “Clevor” engine build, and were the factory configuration of the fabled BOSS 302 engines.
Leave It To Clevor
The modifications required to install Cleveland heads on a Windsor block are minor in the grand scheme of things. The water passages in the cylinder heads need to be altered, you will have to use different pistons to clear the larger valves and altered valve angle, and obviously, a Cleveland-specific intake manifold. But why go through the trouble? What is the purpose and what are the power gains compared to that of using Windsor heads? Sure, back in the day when there wasn’t a plethora of great-flowing aftermarket Windsor cylinder heads on the market, moving to a monster Cleveland head made sense. But, what about now, in modern times?
This is what we aim to find out, by building a Windsor engine and placing it on the dyno. Then, we’ll tear it back down and convert it to a Clevor engine. Most of the time, Clevor builds are used with a 351 Windsor platform with a deck height of 9.500 inches. However, for this test, we will be using a 302-based engine with a deck height of 8.200 inches instead of a 351. Our ultimate goal is to replicate a BOSS 302 and stroke the engine to yield 347 cubic inches.

The rotating assembly will mostly stay the same between the two configurations. The forged 4340 steel 3.400-inch-stroke crankshaftt and 5.400-inch H-beam connecting rods are from Liberty Performance Components, and are very typical of what you’ll see in any 347 short-block.
Apples To Apples
So, let’s be clear on what our intentions are here. We are going to build a 347 Windsor-based engine. The engine will have a dual plane intake with aluminum heads, roller camshaft, and flat-top pistons. Once we tune the engine on the dyno and establish the horsepower and torque, the engine will be torn down. We will replace the pistons with a set fitted with the appropriate valve reliefs for the Clevland head which will have the same compression ratio. We will take a set of aluminum Cleveland heads with the same combustion chamber size and intake port volume and modify the water ports for the Windsor block. We will then install the cylinder heads and an aluminum Cleveland-style dual plane intake and dyno test again. The cubic inches will not change only the pistons, heads, and intake. Of course, the headers will be different due to the exhaust port configuration but the primary pipe size along with length will remain the same.

The MAHLE PowerPak pistons measure 4.030 inch in diameter and are an off-the-shelf flat-top application. Designed for standard 20-degree inline-valve heads, the pistons have all of MAHLE’s standard performance attributes, like a phosphate coating, hard-anodized ring grooves, and Grafal anti-friction skirt coating.
The 347 Windsor Engine Build
The short-block of the engine will remain largely the same between the two tests, but for the first test, let’s dive into the Windsor build. The block is a roller 302 block out of a early ’90s F150 that has been fully machined with the bores opened up by .030 inch. A forged 4340-steel Liberty Performance crankshaft with a 3.400-inch-stroke was dropped in the mains with standard DuraBond bearings. Hanging off the crank are a set of Liberty forged 4340 H-beam connecting rods, measuring 5.400 inches center-to-center.
The pistons for the Windsor build were off-the-shelf MAHLE PowerPak pistons. (P/N: 930146830) that would be at home in any 347 stroker build. Made from 4032 forged aluminum, the pistons have a 1.0mm, 1.0mm, 2.0mm ring pack and a flat top with 6.5cc standard Windsor valve reliefs. The included MAHLE ring set uses a plasma-moly-coated ductile-iron top ring, a cast-iron, taper-face second ring, and standard-tension stainless oil ring. Like all PowerPak pistons, the 4.030-inch slugs are phosphate-coated with hard-anodized ring grooves and have a Grafal anti-friction skirt coating applied.
Edelbrock Performer RPM Windsor Cylinder Head
The real stars of this particular test are the Edelbrock Performer RPM cylinder heads utilized. P/N: 60255 are set up for a hydraulic-roller-equipped street performance application in the 350 to 500-horsepower range. Cast from A356 aluminum, the Performer RPM heads have a 190cc intake port, which feeds a 2.02-inch intake valve. The 1.600-inch exhaust valve exhales into a 60cc exhaust port. The 11/32-inch-stem valves are housed in a 60cc combustion chamber with 45-degree valve seat angles as part of a 3-angle valve job, out of the box.
The Edelbrock Performer RPM cylinder heads have an as-cast 190cc intake runner and 60cc exhaust runner along with a 60cc combustion chamber. They come fully assembled and ready to bolt on with 2.02-inch high-flow intake valves and 1.600-inch exhaust valves. The included valve springs are designed for hydraulic-roller cam profiles and will handle up to .575 inch of lift out of the box.
The heads are also outfitted with 3/8-inch rocker studs and valve springs able to handle up to .575 inch of lift from a hydraulic roller cam. Out of the box they flow 255 cfm at .600 inch of lift on the intake and 174 cfm at the same .600 inch of lift on the exhaust. The Windsor version of the Performer RPM heads have the stock 20-degree inline valve angle and utilize all of the standard Windsor components in a bolt-on affair.
COMP’s Windsor Valvetrain
For this test, we went to the tech department at COMP Cams and laid out what we wanted to do. In order to make the test as representative as possible, they whipped up a couple of custom cams for the test. On the Windsor side, we ended up with a camshaft measuring .562 inch of lift on the intake side, and .569 on the exhaust, with a split duration of 218 degrees at .050-inch lift on the intake and 226 degrees on the exhaust.

The COMP link-bar Retro-Fit hydraulic roller lifters will be used in both of the cylinder head tests. While we will be using COMP Magnum roller rocker arms for both tests, they will be different part numbers, due to the differences in valve arrangement and rocker ratio required.
Riding on the cam’s lobes are a set of COMP’s Retro-Fit hydraulic-roller link-bar lifters. The lifters are designed to allow an easy conversion from flat tappet lifters, but work equally well as upgrades from the standard dogbone-and-spider lifter setup. We opted for them for their reliability and strength, with heat-treated lifter bodies, precision-fit pistons to limit leakdown while allowing air to escape for a faster pump up upon startup, and long-life roller assembly. They are the factory .875 inch diameter and come in at a scant 146 grams per lifter.
A 5/16-inch, .080-inch wall-thickness hardened pushrod connects the lifter to the COMP Magnum 1.6:1 roller rocker arm. The Magnum rocker arms are constructed from 8620 steel for maximum strength and stiffness at an affordable price point. They will handle up to 350 pounds of spring pressure and are a great choice for this type of build.
The cylinder heads, along with the rest of the engine, are sealed with an Edelbrock gasket kit. The .045-inch compressed-thickness head gasket brings the total compression ratio for this engine combination to right about 10.25:1. Quite a healthy combination that would make for a blast on the street, if the engine were staying in this configuration. Topping off the combination is an Edelbrock Performer RPM dual-plane intake manifold. Designed for higher-RPM street use with a carburetor, it’s listed as having a 1,500 to 6,500-rpm powerband, which is right where this engine would live on the street.

We’re using an Edelbrock Performer RPM dual-plane carbureted intake on the Windsor build. Even as a dual-plane manifold, its listed powerband is 1,500 rpm to 6,500 rpm, which is where a 347 typically lives.
In order to provide fuel for the test we’ll be using the same carburetor on both combinations, and that’s an 800cfm Edelbrock AVS2. The AVS2 series carburetors are designed to balance wide-open throttle performance with impeccable street manners. The AVS2 is available in 500cfm, 650cfm, and 800cfm variants, and the tech team settled on an 800cfm model for our project. Out of the box, it should perform plenty well on both combinations, providing enough airflow and fuel to make all the power the engines are capable of.

An 800cfm AVS2 carburetor will be pulling double duty on both combinations. Because of that, we’re sticking with the out-of-the-box jetting, as the engine seemed quite happy with the setup.
Setting The Baseline For The Comparison
With the 347 assembled with the Windsor heads, we fired up the dyno to get our baseline. A 10:1 Ford 347 with Performer RPM heads and a dual-plane intake isn’t exactly an uncommon combination, so we had an idea of what it would make going into the testing. For both tests we are using 93-octane pump gas and an MSD distributor with an MSD ignition box. The ignition timing was really the only parameter adjusted on the dyno once the engine was broken-in and power pulls started.
This particular engine combination with the Performer RPM Windsor cylinder heads liked total timing of around 32 degrees. For an out-of-the-box engine we felt like the power numbers were very comparable to what was expected and very strong overall. Those numbers were peaks of 453.8 horsepower at 5,500 rpm and 468.2 pound-feet of torque at 4,400 rpm. Over the 3,900 rpm to 5,600 rpm sweep, we saw an average of 410.9 horsepower and 455.4 pound-feet of torque. That would make for a great street cruising engine in a Fox body, or really anything you would put a small-block Ford into.
These numbers will serve as the baseline in the comparison. In the next article, we’re going to swap the pistons out, install the 190cc Cleveland versions of the Edelbrock Performer RPM cylinder heads, and see whether the Cleveland architecture has an advantage in this day and age. So, stay tuned!

Definitely nothing to sneeze at here. 453 horsepower and 468 lb-ft of torque will make for a great street beast. Or, it would if we weren’t popping off these heads and installing the 190cc Cleveland versions of the Edelbrock Performer RPM. By keeping things as similar as possible, we plan to find out whether the Cleveland head has an advantage in today’s landscape.