Jim Smart
March 12, 2014

Debuting in the '93 Lincoln Mark VIII luxury coupe, the 4.6L DOHC Modular V-8 quickly transformed a quiet, sedate luxury coupe into a high rpm screamer with a stab of the throttle. The modular V-8 is a natural born hot rod right off the assembly line, and a powerful engine swap for your vintage Ford.

What makes the 4.6L and 5.4L DOHC engines different than your 302 or 351W, aside from the obvious overhead cam design, is the bore and stroke. The Modular V-8 has a smaller 3.552-inch bore, down considerably from your small-block Ford's 4.000-inch bore. When you mix the 3.543-inch stroke (4.6L) or 4.165-inch stroke (5.4L) with a 3.552-inch bore, the Modular V-8 really is a different engine altogether. The 4.6 Modular's small bore and nearly identical stroke (4.6L) makes it a "square" engine where you need rpm to make power; the 4.6L DOHC is not a low-to-mid-range torque engine. It likes to rev, making its peak torque in the 4,000-4,500 rpm range depending upon application.

As with the old cammers, fitment can be tricky. It will fit into a Galaxie or an F-100 truck with ease, but if you're planning to swap it into your Mustang, Fairlane, or Cougar, extensive chassis modifications must be made. Shock towers must be altered or eliminated with an alternate front suspension and engine locating plan.

The Block

The DOHC Modular V-8 has evolved with reliable consistency for more than a decade. Early on, the 4.6L DOHC employed the Teksid F6LZ-6010-AB aluminum block according to George Reid's How To Rebuild 4.6L/5.4L Ford Engines book, which is available from CarTech Books. The DOHC's first aluminum Modular block weighed just 86 pounds compared with the 175-pound SOHC iron block. Teksid of Italy, a world-class aluminum casting operation, provided Ford with DOHC block castings through 2001, when Ford made the decision to bring casting work into its Windsor, Ontario foundry (Windsor Aluminum Plant or "WAP"). Ford introduced a lot of good constructive modifications to the DOHC block including thicker pan rails and increased ribbing for reducing noise, vibration, and harshness (NVH).

Renowned Modular engine builder and racer, Sean Hyland, of Sean Hyland Motorsport tells us he uses the early '96-'98 Cobra Teksid block (F6LZ-6010-AB) for his drag racing engines with great success because they can withstand 1,500 horsepower. This block was also used in the '93-'98 Lincoln Mark VIII, which means there are plenty of cores out there—higher mileage cars can be had for as little as $1,000. Italian-cast Teksid blocks are cast in SAE 319 spec' aluminum and heat-treated to get the desired strength. The Teksid block is consistent and predictable throughout its 1993-2001 production life according to Hyland. The only change was a switch to wider interference fit main caps in 1999 in a revised block casting (ZR3Z-6010-CA) when Ford eliminated the main cap cross bolt jackscrew preload design.

Early in the new millennium, Ford Racing came out with two new aluminum blocks—M-6010-A46NA and M-6010-A46SC. The A46NA block was conceived for SOHC and DOHC use and will work with 2V, 3V, and 4V heads. These two aluminum blocks were cast during the final phase of 4.6L aluminum block production with a chilled bulkhead casting process for stronger main webs. Main webs were also rounded for reduced stress issues. Wider 17mm main caps are ball-burnished for good bearing security.

The A46SC block is designed as a drop-in replacement for '03-'04 Cobra Mustangs, though it can be used with any of the Modular cylinder heads. There's also the M-6010-T50 FR500 aluminum block from Ford Racing bore-sized for 5.0L of displacement (3.700 inches) with an 8.9370-inch deck height. The disappointing side of these three blocks is availability. Production has discontinued and they're no longer available from Ford. This means you will need to look to aftermarket suppliers like Modular Mustang Racing and Summit Racing Equipment and check available inventory. Availability is also an issue with DOHC cylinder heads of all types. Most are out of production, so you'll be at the mercy of inventory in the aftermarket.

1 After debuting the cammer in the 1993 Lincoln Mark VIII, Ford later upgraded the engine with hotter cams, a high-performance intake manifold, and a host of other nice performance features. In 1996, the 305hp 4.6L DOHC was introduced in the SVT Mustang Cobra, and the new-wave, 32-valve four-cam Modular made the Cobra Mustang the most advanced Mustang ever at the time.
2 The Italian-cast 1993-2001 Teksid block is the original 4.6L DOHC block, tipping the scales at 86 pounds. It is easily identified by its waffled aluminum surfaces and Ford casting numbers.
3 The Teksid DOHC block was produced in two basic forms from 1993 to 2001. From 1993 to 1998, the F6LZ-6010-AB block with jackscrew cross-bolted main caps was produced for all DOHC applications including Mustang and Lincoln Mark VIII. In 1999, Ford revised the Teksid block to interference fit main caps eliminating the jackscrew preloaded main caps, which is XR3Z-6010-CA.
4 Here’s the “WAP” DOHC block Ford produced in house at its Windsor Aluminum Plant beginning in 2001. The WAP block is lighter than the Teksid at 80 pounds. Ford revised the main bearing webbing for improved strength along with improved oil drain back to get oil away from the crank for reduced windage. This block employs a thicker pan rail for improved noise, vibration, and harshness. Though the WAP block offers less weight and improved NVH characteristics, Hyland prefers the Teksid block for applications above 600 horsepower.
5 This block casting shows 4G7V-6015-AC, which is the M-6010-GT and M-6010-GTWS block exclusively for the Ford GT super car. This block was produced in very low numbers and averages $5,000 to $8,000 in price if you can find one at all. The GT’s 5.4L 356-T6 aluminum block tips the scales at 110 pounds with 90.2mm bores. This is a dry sump block, but it can be machined for wet sump operation.

Rotating Mass

The 32-valve DOHC engine is loaded with ironies. You'd think this high-revving high-performance V-8 would be fitted with a steel crank, heavy-duty forged connecting rods, and forged slugs. It wasn't. From 1993 to 1995, the DOHC was factory fitted with a cast crankshaft and powdered metal connecting rods like the SOHC engine.

Although "powdered metal" sounds wimpy, it isn't. The DOHC's powdered metal cracked connecting rods will take a pounding in a naturally aspirated engine. They're called "cracked" because the one-piece rod is "cracked" at the big end during manufacture just to make sure caps aren't mismatched or installed backwards; it only goes together one way.

Powdered metal connecting rods are adequate for DOHC applications under 500 horsepower. Beyond that, look to I-beam or H-beam connecting rods and forged pistons with coated skirts.

A stock rebuild can get by with powdered metal rods and hypereutectic pistons. Why hypereutectic pistons? Because forged pistons have a more aggressive expansion rate and can be noisy when cold because we need to allow more expansion room in our clearances. Once warm, they perform admirably.

Ring width boils down to what you intend to do with your DOHC. If you're going racing, narrow ring widths reduce friction and free up power, but you sacrifice durability in street use. And this is how you choose a piston package.

6 Crankshaft selection for the DOHC is simple—six-bolt or eight-bolt flange. You will want the eight-hole for your DOHC. Cast or steel crankshaft? Ideally, you will choose steel, which gives you a DOHC to grow into. Contrary to popular belief, not all Cobra engines got a steel crank. Most were high-nodular iron. Sean Hyland tells us he has never seen a broken cast crank in the DOHC, and believes it can take up to 500 horsepower. Most DOHC applications from 1996-up are steel cranks. Supercharged applications got Manley rods and forged pistons in addition to a steel crank.
7 Like the SOHC Modular, the DOHC employs a main thrust shim, which works like a main thrust bearing only you’re able to adjust crank endplay with this approach. This is a very clever system of endplay adjustment because you can fine tune thrust by varying shim thicknesses.


Monster Mash

For 2000, Ford built the ultimate Cobra-R with the tall-deck 5.4L DOHC V-8. Where the 5.4L DOHC differs from the 4.6L is its iron block topped with the Ford GT supercar's cylinder heads. It produced a healthy 385 horsepower and 385 pound-feet of torque. Though the Cobra R's 5.4L DOHC engine used the iron Windsor truck block, it was fitted with special pieces like a steel crank, Carillo rods, forged pistons, and specially modified 32-valve heads. This is a DOHC you can build yourself using off the shelf parts, though the intake manifolds are very hard to come by these days.

All 4.6L DOHC engines came from the factory with cracked powdered metal connecting rods except the ’03-’04 supercharged Cobras, which received Manley rods and forged pistons for obvious reasons. Cobra engines prior to ’03 got hypereutectic pistons just like the SOHC engines. This hypereutectic piston/crack powdered metal rod combo has been very successful in high-performance applications. If your goal is 500-plus horsepower, go with forged pistons and forged steel rods.
Aftermarket companies such as Coast High Performance and Eagle Specialty Products offer complete stroker kits for SOHC and DOHC alike, including steel cranks, H-beam rods, and forged pistons, enabling you to increase engine performance.


Lubrication

Instead of being driven off the camshaft like a small-block or FE-series, the DOHC Modular's 13mm G-rotor oil pump is driven by the crankshaft. According to Sean Hyland, every new oil pump should be inspected right out of the box for casting flaws.

Pump rotor clearances (cover and rotors) should be 0.002-inch according to Hyland. If clearances are any tighter than 0.002-inch, do not use the pump. If clearances are too loose, Hyland suggests lightly working the pump surfaces on a perfectly flat surface with 600 grit sandpaper and a petroleum based solvent. Plate glass makes a perfect working surface beneath the sandpaper to achieve a the desired results. While you have the pump apart, check the relief valve for proper operation. It should be installed in the right direction and move freely within its bore. For heavy duty applications, billet pump gears or Melling's cast iron pump (PN 10227), is recommended.

Another often overlooked pump issue is getting the pump centered on the crankshaft. Bolts and holes do not provide perfect pump and crankshaft alignment, which must be performed by hand before you tighten bolts. Pump misalignment causes unnecessary side loading and stress, which can lead to pump failure.

8 When installing the Modular’s oil pump, it should be perfectly centered on the crank so there is no side load. Side loading will cause pump failure and engine damage. The factory F8OZ-6600-AA aluminum Cobra oil pump features a 15⁄16-inch pick-up and 13mm wide rotor and cavity.
9 This is Melling’s #10227 cast-iron Cobra pump with 13mm wide steel billet rotors and 15⁄16-inch pick-up. It provides an 8-percent increase in pump volume. It’s a must for severe-duty applications.

Cylinder Heads

The DOHC's factory cylinder heads have continually eveolved over the years. In its infancy, the DOHC Modular was fitted with twin-port heads also known as B-series heads. Ford referred to this early DOHC head as the Swirl Port, but the twin or "B" designation is more representative of the port's shape. The square, throttle-operated primary port operates below 3,000 rpm. The round, vacuum-operated secondary port comes into play above 3,000 rpm, much like secondary throttle plates do in a carburetor. The Twin Port heads are preferred by some Modular enthusiasts, however, there are better cylinder heads.

In 1999, Ford pressed the Tumble Port head into service, which featured a large single intake port that did a better job of keeping fuel droplets in suspension, hence the word "Tumble Port." Hyland tells us this head works very well at up to 0.450-inches of valve lift. Exhaust ports on the Twin Port and Tumble Port are virtually the same. The Tumble Port gives the 32-valve Modular better low-to-mid-range torque and more horsepower on the high end.

In 2002, the C heads were updated for greater exhaust flow, with a mild increase on the intake side. These were employed in the '03-'04 Cobra, Mach 1, Aviator, and Marauder. The 2000 Cobra R had it's own specific head design that later grew into the Ford GT and GT500 designs.

Induction

The DOHC's original induction system installed in the Mark VIII was produced and designed for the Twin Port head and consisted of a throttled primary port and a vacuum-operated secondary throttle assembly known as the Intake Manifold Runner Control (IMRC). Hyland discourages the use of Twin Port heads and induction, especially if you're going above 6,000 rpm. At low- to mid-range rpm, you need long intake runners that make air velocity and torque. At high rpm, you need short intake runners for top-end horsepower. The twin port/secondary throttle approach is restrictive, which is why it is ineffective above 6,000 rpm.

The Cobra's Twin Port induction package uses revised computer programming to open the secondary IMRC throttle plates at 3,200 rpm for improved airflow and power. For 1998, Ford went to a plastic IMRC for less heat transfer according to Hyland, and this is the IMRC to use. You want F8ZZ-9U531-AA for the righthand side and F8ZZ-9U531-BA for the left. Gaskets are F7LZ-9461-AA. Hyland mentions the IMRC eliminators, which were once available from Ford Racing. When you eliminate the IMRCs, you gain horsepower because you're operating on both ports all of the time; the tradeoff is a reduction in low-end torque.

The '99-up Tumble Port head utilizes a different induction package with eight intake runners instead of 16. Hyland says a 20-cfm gain can be had with porting, but it is of little benefit in terms of power. The FR500 intake manifold fits the FR500 cylinder heads perfectly and can be used with the Tumble Port and Mach 1/Cobra cylinder heads with minor modifications. The FR500 head/induction package works on a principle of long and short intake runners separated by secondary throttle assemblies similar to the Twin Port. The aftermarket, of course, offers a variety of induction systems for the Twin Port, Tumble Port, Mach 1/Cobra, and FR500 cylinder heads.

10 The reason why Ford’s overhead cam Modular makes more power is cam profile and the nature of these very large, low-friction cam lobes. This cam technology spreads the load over a larger surface area and allows for a more aggressive profile while reducing friction. Valves and springs are much smaller and lighter, on par with a motorcycle engine where you can spin this guy high and make more power.
11 The DOHC’s timing chain system works exactly the same way as the SOHC except there is an additional chain up top on each side to drive the second camshaft. Oil-pressure-fed tensioners maintain pressure on chain guides.
12 Tumble Port (left) and Twin Port (right) demonstrate DOHC cylinder head function. The Twin Port operates on the square primary port below 3,000 rpm. Punch the throttle and you get round secondary ports for high rpm horsepower. The revised Tumble Port head from 1999-up improves low- to mid-range torque and gives you more high-rpm horsepower.
13 On the left is the 1999-up Tumble Port with a larger 54cc combustion chamber. On the right is the original Twin Port with a 52cc heart-shaped chamber. The Twin Port offers a combined flow of 231 cfm from both intake ports at 0.500-inch valve lift. The Tumble Port yields 225 cfm intake flow at 0.500-inch valve lift. Exhaust flow is the same at 0.500-inch. The later ’03-’04 Cobra/Mach 1 head delivers the same intake port volume at 177cc, but greater compression thanks to a smaller 52cc chamber. Intake flow is 233 cfm. Exhaust flow is greater than the Tumble Port at 169 cfm.
14 There are a number of induction systems available for the DOHC Modular induction factory intake manifolds. If you’re building a Twin Port DOHC, your options are few, which is incentive to consider the Tumble Port, Mach 1/Cobra, or FR500 head. This is a dual-purpose DOHC intake manifold from Sullivan Performance. It works with electronic fuel injection and it will accommodate a Holley carburetor flange.