Parts selection is one of the most important elements of engine building because all parts must operate in concert with one another. Never has this been more crucial than with Ford’s Modular V-8 because of the many variations produced since 1991. You can interchange a lot of parts with these engines if you have the means (knowledge and a good machine shop) to make modifications that allow parts to interchange. The greatest differences exist between the two Modular engine plants: Romeo, Michigan, and Windsor, Ontario. Romeo tends to be more passenger-car oriented while Windsor caters more to the truck segment, but there are exceptions to this rule. I have seen passenger-car engines produced at Windsor, and truck engines that have been produced at Romeo.
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If you’re rebuilding an existing engine, I suggest making improvements that yield more power without sacrificing drivability or breaking the budget. I also suggest keeping the same basic engine. If your engine is beyond salvage, build a new one with the same type castings from scratch or find an identical core from a similar vehicle. In other words, if you have a 1998 Mustang GT, find a 1996–1998 Mustang GT core engine.
Keep in mind that the 4.6L and 5.4L SOHC engines are as common as doorknobs, so finding rebuildable cores is easy. Buying new parts is just as easy as, and sometimes easier than, rebuilding old cores. The path you take depends on your budget, the time you have available for rebuilding, and what you want to achieve with your Modular V-8.
If you’re starting from scratch, you have a lot of parts to consider, so you better put together a build-up plan. Since its introduction in 1991, there have been untold combinations of blocks and heads, including the three-valve engine introduced in 2004. When you think of Modular engine components, you have to think Romeo and Windsor and what you’re going to build. Although they generally look the same at a glance, they are different from a parts interchange standpoint.
4.6L Engine Differences
From 1991 to 1996, there was just one Modular engine plant: the old Ford tractor plant in Romeo, Michigan. When Ford sold its tractor division to New Holland in the late 1980s, it had empty factory floor space in Romeo. Ultimately, a new generation of fuel-efficient, and emissions-friendly overhead cam V-8 engines was built in Romeo.
It took Ford many years to develop a new family of overhead cam V-8 engines. Ford spent well over $1 billion developing the 4.6L SOHC Modular V-8 first introduced in the 1991 Lincoln Town Car. Ford’s intent was to roll this high-tech engine into as many car and truck lines as possible. It was not an easy transformation for Ford. Because the Modular V-8 was massive, vehicle design had to change radically to accommodate the fender-to-fender mass. In its most basic SOHC size, the Modular engine was wider than the massive 1969–1970 Boss 429. Every single Ford, Mercury, and Lincoln nameplate ultimately had to change significantly for this engine to fit.
Beginning in 1995–1996, the Windsor, Ontario, engine plant across the Detroit River from Detroit began producing 4.6L and 5.4L SOHC iron engines for trucks and large SUVs. Windsor is primarily a truck engine plant, although it has produced engines for passenger cars, such as the 1999–2000 Mustang GT. By the same token, Romeo has produced engines for trucks as well. Windsor came online initially to produce Modular V-8s for the all-new 1997–1998 Ford F-150 and Expedition, then the Excursion, Super Duty trucks, and E-Series vans.
As you delve into engine components, the differences in these engines become readily apparent.
SOHC block identification from 1991 to 1995 is simple because Romeo was the only engine plant. These are marked “R,” but not all block castings are so marked, which is why you must also be attentive to casting and part numbers, as well as physical differences. Romeo blocks have always been cast at Ford’s Cleveland foundry, which means they are cast with the “CF” Cleveland Foundry logo.
Beginning in 1996, a second plant and foundry in Windsor, Ontario, was used. Windsor blocks are generally marked with a “W.” I haven’t seen a Windsor block yet that hasn’t been marked with a “W.” I have, however, seen Windsor blocks cast at both Cleveland and Windsor foundries.
Main cap security is another way to identify blocks. Romeo blocks have main cap jackscrews and cross bolts. Jackscrews are for adjustment (specific torque) during installation. Cross bolts secure jackscrews and main caps.
Windsor blocks have dowel pinsecured main caps and cross bolts. After main caps have been properly torqued, dowel pins are hammered into place and cross bolted. This makes Windsor blocks easier to assemble, taking less time. It has yet to be determined which is a better system.
Aside from main cap configuration, Romeo and Windsor SOHC blocks are essentially the same with some variations. Romeo blocks, for example, have subtle differences from Windsor blocks in the casting. They are marked the same with the same kind of webbing and ribs. Although both blocks are state-of-the-art, they don’t employ the most uniform cooling I’ve ever seen. There’s a 60/40 cooling circulation split favoring the driver-side cylinder bank. Bore size, 3.540 inches, tends to limit the 4.6L and 5.4L engines. And due to design limitations, both are limited in stroke, too.
Although Ford lists one basic part number (7L2Z-6010-B) for 1991–2008 Romeo passenger car blocks, the Romeo block casting has evolved through the years. Those first revisions came in 1996 for the Mustang GT. The subtle casting improvements were designed to make the Romeo block stronger. For 2008, a Romeo service replacement block is available with two knock-sensor bungs. Otherwise, this block remains virtually unchanged. The Windsor SOHC block (part number F6AZ-6010-BH) debuted in 1996 and hasn’t changed much.
See the chart at right. It is a table of known SOHC block part numbers. Not all numbers appear here, just the more common ones. Expect to find other numbers out there.
Casting Date Codes
Ford block-casting date codes are alphanumeric, much as they have been for a half-century. A casting date code of “6K05” is either October 5, 1996, or October 5, 2006, depending on the casting/part number. Date codes are stamped into the casting and specify the date of manufacture, which breaks down as Year/Month/Day. Date codes found on castings are the actual date of casting at the foundry. Cleveland foundry castings (Romeo blocks) have a circular “CF” logo (Cleveland Foundry), and Windsor foundry castings (Windsor blocks) simply have a “WF” (Windsor Foundry).
Oiling System Fortunately, there aren’t many differences in Modular engine oiling systems, so you have less chance of making a mistake. The SOHC and DOHC engines have different oil pumps, yet they do interchange if you make the right modifications to the pump pick-up and windage tray. If you don’t make these modifications, the engine produces an unpleasant clatter when the rotating assembly just barely strikes the pump pick-up. When you hand-crank the engine on an engine stand, you aren’t able to detect the interference, but when you start the engine, there is contact and a lot of noise. You really must make this modification to the pick-up.
What makes these pumps different is capacity. The standard SOHC pump offers plenty of volume for just about any application. However, if you want an added margin of oiling system security, step up to the high-volume Cobra/ DOHC oil pump. And remember, some modification is required. Do not install the Cobra pump in an SOHC engine without performing required modifications to the oil pick-up.
Melling offers a steel-billet highvolume oil pump (PN 10227) for Modular engines and, although it is heavier, it is more durable than an aluminum pump. It stands up to the rigors of highperformance driving and provides insurance to protect your engine. Also, aluminum pumps are available with steel billet rotors. They don’t come cheap, at around $320, but they’re a good investment for long-lasting engine performance.
FRPP offers the M-6600-D46 HighVolume Oil Pump Kit, which includes the Cobra/ DOHC pump and pick-up. Remember, this pick-up must be modified to work in the SOHC engine. Although it looks as if it clears the crankshaft and connecting rods, it does not. Check clearances closely and ascertain how much room you have between pickup and any moving components. You need a minimum of .060 inch, but I suggest more.
Nodular Iron Crankshaft
Since 1991, only a few basic crankshafts have been used in Modular engines. Nodular iron Romeo cranks are six-bolt flange units that have proven to be very reliable in a broad range of applications from family sedans to high-performance Mustangs to Crown Victoria Police Interceptors. According to many Modular engine builders, you may have a light crank or a heavy crank, depending on what type of connecting rod was used.
The nodular iron crankshaft is extremely durable. Ford uses it in the Mustang GT’s SOHC two-valve and three-valve Romeo engines. PowerHeads, which builds lots of Modular engines, says it has never seen anyone break a nodular iron Modular crankshaft. I’ve heard the same story from Sean Hyland of Sean Hyland Motorsport, who builds Modular racing engines. He says the nodular iron crankshaft is good for up to 500 hp. Sean suggests the eight-hole flange over the six-hole if you are going to twist it high and tight.
The quickest way to identify a heavy or light nodular iron crankshaft is the balancing holes in the counterweights. Heavy cranks have deep drill holes for balancing purposes. Heavier nodular iron crankshafts were built for heavier connecting rods, which first entered service in 1996. It is believed that these heavier rods were used in the Mustang GT’s 4.6L SOHC engine. Romeo has consistently stayed with the six-hole crankshaft except for steel DOHC crankshafts, which are primarily eight-hole flange units.
The eight-hole crankshaft has been a Windsor mainstay because most Windsor engines have been built for F-Series trucks and E-Series vans. Expect to see eighthole nodular iron Windsor crankshafts, which are good street units for high-performance applications. The 5.4L crankshaft has a longer stroke. Always check stroke and the crank’s casting number. Also keep in mind that Romeo has never produced a 5.4L SOHC or DOHC engine. All 5.4L cranks have eight-hole flanges.
You can choose from four basic types of harmonic balancers for Modular engines, with six or eight ribs, depending on application. The 4.6L engine employs a six-rib harmonic balancer, and the larger 5.4L engine uses an eight-rib balancer. Choosing the right balancer is crucial to engine life, specifically oil pump life. This is why you must be very careful if you intend to use an aftermarket balancer. I’ve learned from a number of seasoned Modular engine builders that some aftermarket balancers vibrate the oil pump gears badly, resulting in pump failure.
With pump failure, you have vibration issues or undue stress around the crank snout, which takes a toll on both the pump and crankshaft. Vibration is transmitted along the crankshaft, finding and damaging an engine’s internals. Modular engines are internally balanced, so I usually don’t consider balancer and flywheel issues. However, you might want to discuss this issue with an engine builder because I’m inclined to recommend balancing with a balancer and flywheel, just to eliminate potential vibration problems. This means custom balancing for smoothness, but that can create a host of challenges for some builders. Your builder is the best judge of whether to internally or externally balance.
I call it a timing system because it is more involved than a conventional overhead valve pushrod V-8 timing set. Because the 4.6L SOHC is an overhead cam design, you have to figure out how to turn the camshaft in each head at the proper time. Although the Modular’s timing system seems overwhelming, it is actually quite simple and easy to time because Ford added clearly visible timing marks.
Prior to the 2000 model year, Romeo Modular engines were fitted with steelbacked, nylon, plastic-lined chain guides,which do an excellent job. From 2000–up, Ford used plastic timing chain guides in Romeo engines, which are lighter in weight and offer quieter operation.
Let me clarify something about steel versus plastic chain guides. Windsor used plastic chain guides from the beginning in 1997, while Romeo was still using steel guides. Romeo didn’t start using plastic chain guides until 2000, but do not be surprised at anything you find out there. Jim Grubbs of JGM Performance Engineering said he expected the plastic chain guides to last virtually forever. However, I suggest replacement in the interest of reliability, which eliminates any doubt.
Timing gears and crankshaft reluctor rings are often a source of confusion. Two types of crankshaft reluctor rings are available: cast and stamped. A cast steel sensor ring is fitted to 1991–2000 engines; the stamped steel sensor ring first appeared in 2001. The stamped steel ring weighs less and costs less to make. With the stamped steel reluctor ring, teeth must face toward the timing cover, never toward the block. Aim them toward the block and you wind up with severe engine damage because they hit the timing chain.
Romeo engines use bolt-on cam sprockets; Windsors have pressed-on sprockets with bolts. Keep this in mind when you order cams and cam sprockets. Cam sprocket spacers are another sticky wicket that can bite you hard if you’re not paying attention. DOHC cam sprocket spacers are wider than SOHC spacers, so don’t make the mistake of installing DOHC cam sprocket spacers on an SOHC and vice-versa. If this mistake is made, interference and chain alignment issues will wreak extensive engine damage.
According to Modular engine expert Sean Hyland, all Modular engines have cracked powdered-metal connecting rods except the 2000 Cobra R (fitted with forged Carillo rods), the supercharged 2003 Mustang Cobra (fitted with Manley forged-steel rods), and the supercharged 2007–up Shelby GT 500. Although performance buffs have resisted using cracked powdered-metal connecting rods, these rods are strong enough for most high-performance applications. These rods are extremely durable as long as they receive a healthy supply of oil and are not subjected to extreme use. Powdered-metal technology makes it more cost effective to produce connecting rods this way. But that doesn’t mean these rods can’t stand up to a heavy foot.
For everyday driving and occasional weekend racing, the Modular’s powderedmetal connecting rod performs very well. JGM Performance Engineering has shown that these rods can indeed be reconditioned, but not in the conventional sense. Instead of cutting rod caps, which cannot be done with cracked rods, you simply hone the large end to .002-inch oversize and return the rod to service using an oversize (outside diameter to fit the rod) rod bearing. The inside diameter depends on how much you machine the rod journal undersize.
Once powdered-metal connecting rods reach 200,000 miles, they are theoretically at the end of their service life and should be replaced. Sean Hyland says he has seen some mid-beam failure because these rods were subjected to detonation, nitrous oxide, and supercharging. It is simply courting disaster to run nitrous or a supercharger with powderedmetal connecting rods. If you intend to run nitrous or install a supercharger, step up to a Manley H-beam connecting rod to be safe.
If you have a healthy checking account, the Manley Pro Series I-beam rod, fitted with ARP bolts, provides incredible strength and durability for engines over 500 hp. If you’re building a more powerful engine, the Manley 300M rod withstands well over 1,000 hp. For most 4.6L SOHC street engines, powdered metal is enough.
Since 1991, the Modular V-8 has received dished Teflon-coated hypereutectic pistons. The only exceptions have been the 2003 supercharged DOHC Mustang Cobra and 1999–2003 Ford F-150 Lightning truck, which were factory fitted with dished forged pistons. However, Ford used flat-top forged pistons on the 2000 Cobra R, 2007–up Shelby GT 500, and Ford GT. So why run hypereutectic pistons instead of cast or forged? Hypereutectic pistons, cast of a high-silicon alloy, enable car makers to run tighter tolerances because they don’t expand much with heat. These tight tolerances (especially piston-to-cylinder wall) allow for better oil control (lower emissions and longer engine life) and consistent cylinder sealing. Plus, tighter tolerances reduce piston noise. This is why Ford recommends running super-low viscosity 0W/20, 5W/20, and 5W/30 engine oil in all Modular engine applications. In addition, tight tolerances also reduce hydrocarbon contaminants in the oil and in the air.
Piston identification can be tricky because all Modular pistons generally look the same. However, you must be aware of their differences. Most non-PI (NPI) SOHC engines have an 11-cc dish along with a 51-cc combustion chamber. The PI head has a smaller 42-cc chamber, which calls for a piston with a deeper 18-cc dish. Matching a set of PI heads with NPI pistons is a recipe for a much higher compression ratio. Naturally aspirated DOHC engines have a much smaller 2– to 3-cc dish and a completely different fourvalve chamber design. The 2004–2008 SOHC three-valve engine employs a lowfriction flat-top hypereutectic piston with Teflon-coated piston skirts.
If you’re building a stock 4.6L SOHC engine, the Teflon-coated hypereutectic piston is your best choice. If you intend to lean on it hard and are anticipating supercharging or nitrous, select a forged piston along with a Manley H-beam connecting rod. Two basic pistons are offered in 2618 and 4032 alloys. For high-performance engines, especially ones running a lot of boost, you should select the 2618. In fact, I suggest this alloy for all engines rather than the 4032 alloy. The 2618 piston should be attached to an appropriate forged connecting rod with a full-floating pin.
In addition, hypereutectic pistons locate the top ring .150 inch below the crown. Forged pistons push it down a little farther, at .235 inch, so that the top ring is away from excessive heat. Rings in any case stack up at 1.5-mm top and secondary rings and a 3-mm oil ring package.
As mentioned, hypereutectic pistons yield less noise on start-up than forged pistons because, as the engine heats up, hypereutectics expand less than forged. Forged pistons expand significantly with heat, so that growth must be figured into bore sizing, which makes piston-tocylinder wall clearances loose and sloppy when cold. With loose tolerances comes noise on start-up, but there’s nothing to worry about. This also means you need to take it easy on a cold engine until the oil is good and hot, and the parts have expanded to their operating temperature size.
Piston noise has always been a Modular engine issue because of bore/piston dynamics. Hypereutectic pistons are noisy in this engine when cold, and forged pistons are even noisier. However, it isn’t just piston-to-wall clearances that make this engine noisy. It’s what happens to the pistons at BDC. Because the pistons drop well into the crankcase at BDC, they become unstable and wobble, adding a significant amount of noise. Noise levels depend not only on piston type, but piston manufacturing technique. Pistons should be properly factory machined to stay quiet when they reach the bottom of the bore, but not all of them do.
The tricky part about Modular engines transcends piston design. These are thin-wall castings, so cylinder walls tend to flex and bow, especially on the piston’s thrust side, which creates noise and oil control issues. Therefore, piston and connecting rod selection is critical for reliability and performance. You want to look not only at the piston type and material, but the connecting rod ratio as well.
Computing Compression Ratio
When you’re shopping for pistons, you need to know the cylinder head chamber volume, deck and compression height, bore size, and piston dish volume. The quick reference tables on page 64 from Sean Hyland Motorsport make it easy to choose just the right piston for your Modular engine build.
Throughout the Modular engine’s two-decade history, many timing covers have been used for SOHC and DOHC versions. These covers have evolved as Ford has expanded this engine to more and more car and truck lines. Many differences have to do with accessory front dress and belt tensioner/pulley locations. As with other engine parts, Romeo versus Windsor comes into play here. Windsor engines have larger timing cover bolt holes because of larger cylinder head and block bolt holes. Romeo bolt holes are smaller. Romeo timing cover bolt holes must be drilled larger if you’re installing one on a Windsor engine.
Timing covers can be difficult to identify. You should select the timing cover and related front dress parts that are compatible with your particular Modular engine. Otherwise, it becomes complicated and frustrating to match a variety of parts with one another. When you’re shopping for new and used parts, you must be specific about the model year, model, and engine. For instance, you’re going to have a tough time if you select a 1991 timing cover and you’re building a 4.6L engine from a 1998 Crown Victoria because you’re dealing with different front dress. You have to source a 1991-specific belt tensioner and other front dress parts.
Two-Valve Cylinder Head
Cylinder head castings are one of the few Modular engine elements Ford kept simple. DOHC heads are more complex, but they have become simpler with time and engineering upgrades.
From 1991 to 1998, two 4.6L SOHC NPI head types are available: Romeo and Windsor. The Romeo head uses cam journal girdles for strength; the Windsor heads do not. In addition, Romeo heads have smaller timing cover bolt holes than the Windsors. Despite the differences, these heads are interchangeable.
Three-Valve Cylinder Head
In 2004, Ford fitted the 5.4L SOHC with a new three-valve cylinder head. A year later, this head was fitted to the allnew Mustang GT’s 4.6L SOHC engine, yielding nearly 320 hp. Three-valve technology has brought a fresh sound and power to the 4.6L SOHC engine.
Ford’s 4.6L three-valve technology comes with castings and parts that you need to be aware of. Unlike the 1991–2003 SOHC heads, the three-valve heads are passenger- and driver-side specific.
Ford lists four part numbers for the three-valve head:
- 5R3Z-6049-CB (2004–2006, driver’s side)
- 5R3Z-6049-BA (2004–2006, passenger’s side)
- 8R3Z-6049-A (2008, driver’s side)
- 8R3Z-6049-B (2008, passenger’s side)
Note: The following specifications were used in the calculations
Compressed head gasket thickness: 0.036 inch
Head gasket bore diameter: 3.62 inch (3.551–3.581 inch bore)
Head gasket diameter: 3.70
Deck clearance: .008 inch for the 4.6L, .120 inch for the 5.4L
Different deck clearances will affect the final compression ratio
42-cc combustion chamber is the 1999–2004 PI 2-V head
51-cc combustion chamber is the 1992–1998 2-V head
52-cc combustion chamber is the 1993–2004 4-V head
49.6-cc combustion chamber is the 3-V head
Fascinating technology makes the Modular engine exciting and different. Instead of traditional iron or steel-billet machined camshafts, the Modular engine employs composite camshafts constructed of steel tubes and individual lobes that are pressed onto the tube in proper position. This makes the Modular engine’s camshafts lighter and easier to manufacture. Think of the composite camshaft as you would the cracked powdered-metal connecting rod mentioned earlier. This manufacturing process is cost effective and produces lightweight cams.
The Modular engine’s camshafts roll in journals without bearing inserts. A solid oil wedge between the cam and journal virtually prevents wear. These heads can be honed (resized) by a competent machinist if wear is an issue.
These composite camshaft lobes ride on roller rocker arms with hydraulic tappets. Hydraulic tappets work just like hydraulic lifters, controlling lash and keeping the valvetrain quiet. Smaller than usual valvesprings close conventional, smaller poppet valves. Modular engines have tiny valves and springs as you see in a motorcycle engine, which reduces weight and internal friction.
The aftermarket offers a limited selection of camshafts for these engines because Ford originally did a pretty good job of camshaft profiling. And this is true throughout the engine. These are highperformance engines right off the assembly line: high-revving V-8s that sound ferocious and make good power. Where they need help is improved low- to midrange torque. You should select a camshaft that broadens the 4.6L SOHC’s torque curve.
Because these are “square” engines at 3.550-inch bore and 3.540-inch stroke, they make their power toward the high end of their operational range. You want a camshaft that helps your Modular engine make good torque down low for the street, where you need it most.
Two basic types of induction systems are available for 4.6L and 5.4L SOHC engines: “low-profile” for passenger cars and smaller SUVs, and “high-profile” for trucks and large SUVs.
Passenger cars and smaller SUVs, such as Explorer and Mountaineer, have the one-piece plastic intake manifold. F-Series trucks and larger SUVs (Expedition and Excursion) have a larger two-piece intake manifold that combines a castaluminum upper and a plastic lower. This manifold employs longer intake runners for better low-end torque. The one-piece plastic passenger- car manifold has shorter runners for mid- to high-RPM torque.
Plastic intake manifolds were developed because of the need to remove heat (and weight) from the induction system. These manifolds came from the factory with a 60-mm throttle body. However, the aftermarket offers 70-mm throttle bodies to increase airflow. You can gain 2 to 3 hp with the 70-mm throttle body, which almost isn’t worth the expense. But when these incremental performance improvements are added up, you realize a significant gain.
Upper intake elbows (that go between the intake manifold and throttle body) also provide a performance boost. Accufab produces a high-performance billet 70-mm throttle body/elbow combination that has produced 10 additional hp over Ford’s 60-mm piece. Also available is a 1-inch spacer for the passenger-car plastic intake that increases velocity, good for 4 to 5 hp. Think of this spacer like a carburetor spacer, which does exactly the same thing.
The aftermarket offers a selection of intake manifolds for the SOHC engine. Edelbrock, for example, even offers a carbureted manifold for those who just can’t live with fuel injection. Choose an intake manifold for your particular application: street, strip, or a combination of both. For the street, you want long intake runners for producing good low-end torque. For the strip, you need shorter runners for high-RPM horsepower and torque. Most of the aftermarket fuelinjection manifolds make more highRPM power than stock at the expense of low-RPM power.
FRPP offers the SVO intake for SOHC engines fitted with SVO heads. The Bullitt intake, which first became available in 2001 on its limited-edition namesake, provides excellent flow characteristics and complements the PI heads. This intake borrows from DOHC Cobra technology with a twin throttle body and longer intake runners.
Oil Filter/Water Neck
The design of oil filter/water neck attachments varies depending on vehicle type. Most are simple, an oil-to-water cooler where oil gives up heat to engine coolant. Trucks and SUVs have a more complicated oil filter/water neck with oil cooler connections. First-year 1997 F-Series and Expeditions are different than 1998–up because the oil filter was relocated behind the crossmember, where it remains today. If you have a 1997 F-Series truck, use the 1998–up oil filter/water neck attachment that relocates the oil filter.
For all Modular engines, the Cobra DOHC oil-to-water cooler water/oil filter neck is available from FRPP or your Ford dealer parts department as an off-theshelf part. This draws excess heat out of the oil and the engine.
Although the primary focus of this book is the SOHC Modular engine, I’m going to brief you on what makes the DOHC different. The DOHC is a highrevving, high-performance engine equipped with 32 valves and a strong aluminum block with steel sleeves and heavily cross-bolted mains.
During the first five years of DOHC production, Ford used a 314-aluminum block (F6LZ-6010-AB) cast by Teksid of Italy (known as a Teksid block). At just 86 pounds, this is a lightweight block compared to the 175-pound iron SOHC block. Ford did away with the main cap jackscrews for 1999 (PN XR3Z-6010- CA), preloading the main caps with an interference fit. Main caps also grew wider for 1999. Knock-sensor bung size changed too.
For 2001, Ford brought DOHC block casting in-house and used a new 319- aluminum alloy at its Windsor Aluminum Foundry (WAP). Ford thickened the pan rail and added ribbing to quiet the DOHC Modular block. Sean Hyland says the later WAP block withstands 600 hp, and he recommends the Teksid block, which can take up to 1,500 hp. There are varying opinions around the industry about this. Others, such as Ralph Pici of PowerHeads, prefer the WAP and later DOHC blocks over the Teksid. FRPP also offers newer, improved castings.
DOHC Cylinder Heads
The DOHC cylinder head story isn’t much more involved than that of the SOHC. The B-Series Twin-Port head uses a primary port for low-speed operation and both ports for wide-open throttle. Air is allowed into the secondary port only when the intake manifold runner controls (IMRCs) are open. Although this must have seemed like a great idea in theory, it hasn’t produced serious performance. In actuality, it’s just not worth the money to port these heads and perform other modifications to get them to work well. If you’re rebuilding a 1993–1998 DOHC for your Lincoln Mark VIII or Mustang Cobra, this is a fine cylinder head for the street.
Production Modular engine valveguides are powdered metal, and they don’t always measure up to clearances acceptable to reputable engine builders. Factory tolerances are .002-inch intake valvestem-to-guide and .003-inch exhaust valvestem-to-guide. Sean Hyland recommends .0015-inch intakes and .0018-inch exhausts to control side motion, as well as bronze or steel guides and stainless steel valves. Factory valveseats are also made of powdered metal, which seems to do quite well even under hard use.
How you grind valves and seats depends on how you’re going to use the engine. For street and road racing, the head should have lots of valveseat contact for improved valve cooling. Radius valve jobs are best left to drag racers.
Written by George Reid and Posted with Permission of CarTechBooks