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Ford's 4.6L DOHC V-8 Explained - Cammer Time
Ford's Hot-Blooded 32-Valve Double Overhead Cam Screamer Explained
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 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.
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.
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.
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.
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.
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.