The original AC Bristol was just another British sports car; but once a healthy American V-8 engine was added, it became a legendary high-performance car. Equipped with the 427 side-oiler V-8 engine, the Cobra could accelerate 0–60 in less than 4 seconds. No other limited production car could match that kind of performance in the mid 1960s. Thus engine selection largely defines the performance, personality, and overall tractability of the car.
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A whole universe of engines can be fitted to a Cobra replica, and this includes the trusty original Ford Windsor and FE engines as well as the Ford Cleveland and Lima powerplants. While some purists maintain that a Cobra replica should be faithful to an original Cobra and house a Ford Windsor small-block or an FE big-block engine, the hobby has embraced all makes and models of V-8 engines. In fact, some are installing GM LS series engines into their Cobra because of the compact design, high-performance capabilities, massive aftermarket support, and ease of installation. While this may be sacrilegious for some, these combinations are becoming more popular.
Your choice of engine should hinge on a number of factors, including horsepower and torque targets (i.e., your ideal powerband), budget, and of course personal preference. Although we decided to acquire the engine parts and have a pro shop assemble our engine, many Cobra owners opt for crate engines for simplicity, convenience, and reliable performance. Many companies can deliver a turnkey engine to your residence. After all, you’re assembling an entire car, and many do not want to build an entire engine from the block up.
Small-Block or Big-Block?
When it comes to powering the Cobra, you have to ask yourself, How much is enough? What kind of handling characteristics are you seeking and how does the engine selection factor into that choice? Most Cobra replicas have a curb weight of about 2,400 pounds. Therefore the car is extremely light and has a power-to-weight ratio that few cars can match. For example, a Backdraft Racing Cobra replica with a 350-hp Ford 302 H/O small-block can propel the car to 150 mph. And that’s just the tip of the iceberg, a high-performance 427-ci stroker smallblock can reliably produce more than 600 hp and put the Cobra’s performance into the stratosphere of supercar performance.
If you opt for a big-block you’re taking on much more weight, but you can easily build an 800-hp engine. Typically, most aluminum big-blocks weigh 150 pounds more than a small-block from the same manufacturer. Adding more weight to the front of the car degrades handling characteristics, and therefore it is less agile through corners.
Whether you choose a small- or big-block engine, you need one set up for your particular application. Hence, the powerband of the engine must match the application. If your Cobra is going to be a street car, then you need an engine that produces good torque from 1,500 to 5,000 because that’s the operating RPM on the street.
A small- or big-block engine with dual quad carbs, single-plane intake, large port heads, and a high-lift, long-duration cam that produces its best power from 6,000 to 7,500 rpm is not suited for the street. But an engine such as this is ideal for road racing because it spends most of its time at high RPM. Drag engines also spend much time at the top end of the powerband. A race-type engine is such a pain to drive on the street because it doesn’t idle evenly at stop lights and doesn’t carburate well at lower RPM. Therefore, you often have to rev the engine and slip the clutch from intersection launches. And it doesn’t pull very hard out of low-speed corners.
The Ford Windsor small-blocks in 260, 289, 302, and 351 displacements as well as Clevelands in 351 and 400 displacements have been popular engines for Cobra replicas since the inception of the market. All of the small-block Fords have a deck height of 4.185 inches and easily fit into the Cobra. You can build these engines with any combination of stock components, but most owners build a small-block using premium components of forged crank, rods, and pistons, and opt for a high-performance set of aluminum heads.
Many Cobra owners opt to build a stroker combination on a stock cast-iron or aluminum block. Many of the stroker assemblies are less expensive than factory-rebuilt parts, so for many owners this is a no brainer and they go with this option. The 302 with 3-inch stroke and the raised-deck 351 Windsors and 351 Clevelands with 3.5-inch stroke are excellent platforms for stroker combinations, as is the 400M, which is a taller-deck Cleveland.
For the 302, stroker combinations in 331, 347, and 355 displacements are popular. And for the 351 and 400 blocks, displacements of 383, 393, and 408 ci are popular stroker combinations. Scat, Eagle, Coast High Performance, and many other businesses offer high-quality stroker combinations to fit Windsor and Cleveland blocks, so you can find a setup that works for your car and application.
The Ford FE 427-ci side-oiler engine was standard equipment in the original Shelby Cobra, and many of the Cobra faithful opt to put an FE engine in their Cobra replicas. The FE (Ford Edsel) engines were built from 1958–1976 to power a wide range of Ford passenger cars, so there are a lot of blocks and engines available. Ford offered the FE in 332, 352, 360, 390, 406, 410, 427, and 428 displacements. A number of stroker combinations are available for the FE engine, including 434, 445, and 505 displacements. Survival Motorsports is a leading FE engine builder and offers a full line of engine components and services for FE engines.
The Ford 385 Series or Lima big-block engines are popular with owners who must have extreme displacement. The 370, 429 and 460 engines were offered from 1968 until 1967, and these replaced the MEL (Mercury, Edsel, and Lincoln) engines. The Lima engines were extensively installed in large passenger cars, trucks, and of course Mustangs and high-performance Torinos. The standard 429 engine featured a two-bolt main bearing cap, cast-iron cam, cast-aluminum pistons, forged-steel connection rods, hydraulic cam, and non-adjustable rocker arms.
The Cobra Jet and Super Cobra Jet became Ford’s most notable bigblocks. The 370-hp Cobra Jet and 375-hp Super Cobra Jet featured fourbolt main bearing caps, 2.25-inch intake, 1.72-inch exhaust heads, and a lot of other high-performance equipment. The Cobra Jet used threadedin rocker arms. The Super Cobra Jet was equipped with forged aluminum pistons, mechanical cam, and 780- cfm Holley carb. These engines were installed in the Mustang Mach 1, Torino Cobra, and many other cars. Many of the standard performance engines have two-bolt main bearing cap block, while the Cobra Jets feature four-bolt main bearing caps.
Of course, as with the small-block, you can stroke the Lima engines. Coast High-Performance offers stroker kits in 502/514, 521/532, and 545/557 displacements.
Many used Ford small-block and big-block engines have been rebuilt and overbored beyond their limits and, therefore, are unuseable. Many owners do not want to pluck a used engine from a Mustang or other performance Ford car and perform a high-performance build up, they want a crate engine. There are many suppliers, such as Ford Racing Performance Parts, Mustangs Plus, Edelbrock, World Products, Roush Engines, Coast High Performance.
Crate engine prices run the entire gamut, and it depends upon equipment package in the engine. Mild-performance, small-block crate engines are sold for $3,000 and more while high-performance smallblocks, with forged rotating assemblies and high-performance heads and valvetrain, start at $5,000.
As with any engine, you need to select the right one for your car. The engine should have the correct equipment package for the horsepower and torque output. A 300-hp small-block crate engine can carry a stock rotating assembly, but if you’re buying a small-block to make 600 hp, it needs to carry forged rotating assembly and other high-performance running gear.
Big-block crate engines are also available from many of the same suppliers, but for a big-block you are entering a new tier of performance and a much higher price. Big-blocks often start at $7,000.
Therefore, when you’re doing research, you need to determine the best engine package for your car and application. Make sure your engine and transmission combination is compatible with your particular kit and whichever crossmember modifications and motor mounts are required to mount it. Call the tech line of a particular crate engine supplier and tell them you’re building a specific Cobra replica, and get all the relevant information to make an informed decision.
Stroker 427 Small-Blocks
For the Mk4, you can use the entire running gear from a modern Mustang. The FFR Cobra has enough room in the engine bay to readily accept the Ford modular motor in either 4.6- or 5.0-liter Coyote iteration. However, as this book goes to press, Factory Five is developing compatible mounts and headers for the new Coyote engine to fit the Mk4. Also, the T-5, T-45 or 3650 transmission, and Ford 8.8-inch differential easily mount to the chassis.
Whether it’s a genuine 1962– 1967 original or a replica, the most important part of the Cobra is the powerplant. And you’re right to think, “The heart and soul of any sports car is the engine.” With the Cobra, it’s especially true. Before Carroll Shelby and Dean Moon stuffed a Ford 260-ci V-8 mill in a 1962 AC Bristol, there was no such thing as a Shelby Cobra. The Ford small-block V-8 engine is what first transformed the beautiful little aluminum sports car from an under-powered, aging roadster to a powerful street performer and winning race car.
But there are many more powerplant options, including some classic Ford engines. The small-block Windsor family of engines, the FE-Series (390/427) and Lima or 385 Series engines, including the 428 and 460, install without great challenge.
Dart Machinery manufactures iron Ford and Chevy small-block V-8 engine blocks as Ford did for the 1960s Cobras. But it also makes them out of aluminum, as we desired. We decided to power our replica with a Dart 351 Windsor-based aluminum engine block that was bored and stroked to produce the magical 427-ci displacement. The genuine Shelby Cobra 427SC had a Ford 427-ci bigblock V-8 that was cast iron and rated at 425 hp. Our engine was the same displacement, yet weighed at least 100 pounds less and produced more horsepower. That’s just the sort of recipe for excitement that Carroll Shelby advocated.
Those original big-block Ford mills had heavy cast-iron cylinder heads. Dart Machinery also produces superlative Pro CNC aluminum cylinder heads. So we ordered all the goods from Dart that we could and sought the company’s advice on what California-based engine builder should create our Dart 427 mill.
QMP Racing Engines
One of Dart Manufacturing’s top pro-engine builders around the globe is QMP Racing Engines. Dart felt that QMP Racing Engines were the bestsuited pro engine shop for the job, so we first did some investigating on the QMP Web site. It didn’t take long for Dad and me to give QMP’s owner, Brad Lagman, a call to talk to him about the Cobra replica project and the engine we wanted QMP to build.
As an automotive author, I’m usually the one asking all the questions. But the tables were turned. Brad very thoroughly interviewed us to discover exactly what sort of engine we’d like to have in our FFR Mk4. After he knew our preferences and goals, he supplied us with a list of components that we should acquire for stuffing our Dart 351W/427 stroker aluminum V-8.
We spent the next bit of time acquiring components through Summit Racing and gathering them all in our living room. After finally collecting everything that we thought we’d need, we drove to Chatsworth, north of Oceanside, with our engine in the car. The Dart Pro CNC aluminum cylinder heads and the aluminum 351W engine block were shipped directly to QMP Racing. And then the painstaking craft of machining, massaging, balancing, blueprinting, and creating our Dart 427 stroker was squarely on the shoulders of the pro builders at QMP Racing.
QMP had the Dart block and cylinder heads line-bored in preparation for our arrival. When we arrived on the scene, we dropped off all those speed shop components and took a tour of the QMP facility.
Project 1: Install Long Block Assembly
Step 1: Hone Cylinder Block and Deburr Cam
With all the cylinders honed to the specified 4.1255 inches and the camshaft bearing housings freshly deburred, install the Comp Cams custom-ground camshaft and flip the engine upside down to screw-in the end-cap studs.
Step 2: Measure Connecting Rod Clearance
Using the dial bore gauge, confirm that the connecting-rod bearing clearance is correct for all eight connecting rods before proceeding.
Step 3: Install Main Bearings
Install the crankshaft bearings and the end caps after the crankshaft is in. Do this before you install the crankshaft to ensure the proper clearances are met between the crankshaft and the main crankshaft bearings. The main bearings go in first.
Step 4: Install Main Bearing Caps
Install the end cap prior to checking it for clearance. First torque the end-cap bolts to spec. Torque the biggest end-cap bolts to 100 ft-lbs of torque. Torque the medium end-cap bolts to 70 ft-lbs. Torque the smallest, outer end-cap bolts to 40 ft-lbs.
Step 5: Check Main Bearing for Clearance
After installing the first main cap, use the dial bore gauge to check the main bearing for clearance.
Step 6: Splay Center Main Bearing
Splay the main bearing in the center of the engine for extra strength. Notice that these end caps are four-bolt caps. Dart Manufacturing uses four-bolt mains for added strength with its mighty aluminum 351W block. A stock cast-iron Ford 351W just has two-bolt mains.
Step 7: Torque Main Cap Bolts
Before checking the clearance of all five of the main bearings, torque the end-cap bolts to spec.
Step 8: Check Main Bearing Clearance
Check all five main bearings for clearance with the dial bore gauge. If you don’t take this precaution, you might install the crankshaft and have it not turn. So avoid problems, and be precise.
Step 9: Inspect Alignment Dowels
After confirming clearance between the crankshaft and the main bearings is within specs with the dial bore gauge, remove the main caps to fit the crankshaft. Alignment dowels enable easy installation of the main caps, a feature found on all Dart aluminum blocks.
Step 10: Install Freeze Plugs in Block
After applying Teflon paste to the threads of the anodized-aluminum 1/4-inch-pipe plugs, install them in the block. All Dart aluminum blocks use 10 threaded, anodized-aluminum freeze plugs. With all the freeze plugs and water drain plugs installed in the block, re-install the main bearings and put a liberal amount of engine oil on each main bearing.
Step 11: Install Crankshaft
After all the main bearings have oil on them, move the forged crankshaft into place. As is common with Ford engines, we added a bit of Mallory metal to the crankshaft to internally balance the engine.
Step 12: Lubricate Crankshaft
One of the most important elements in building a high-performance engine, or any powerplant, is liberal usage of motor oil. Pour some on the crankshaft prior to installing another main cap.
Step 13: Torque Main Caps
Since the crankshaft is to spec for clearance with the main bearings, install the other side of the end caps and torque the bolts to spec. Torque the six 1/2-inch bolts in the center of the block to 100 ft-lbs. Torque the outercenter 7/16-inch bolts to 70 ft-lbs. And torque the outer bolts on the end, the smallest bolts, to 40 ft-lbs. Though possible to install the rear seal after installing the rear main cap, it is not advisable; you can ruin the rear seal. Always install the rear seal, using the supplied plastic alignment tool, before installing the rear main cap.
Step 14:Torque Final Main Cap
Torque the final main cap bolts to proper specs before flipping the engine right side up on the engine-building rotisserie stand.
Step 15: Install Timing Set Gears
Install the timing-set dual gear on the front end of the crankshaft before the engine is flipped right side up.
Step 16: Install Dowels
Pound the installation dowels in place for the collar that holds those timing set gears in place on the crankshaft.
Step 17: Torque Crankshaft Collar
After flipping the engine right side up on the engine rotisserie, carefully install the engine’s timing chain on the camshaft end at the top and the crankshaft end at the bottom. Completing the timing set installation, torque the crankshaft collar to spec.
Step 18: Install Piston Ring
Push the piston rings into place with the piston-ring squaring tool.
Step 19: Set Piston Ring Gap
To determine and to verify that the piston ring gap is correct, use a feeler gauge on the just-ground piston rings. Use the piston-ring squaring tool to set the gap of the piston rings.
Step 20: Install Piston Wrist Pins
After the 16 piston rings are all properly gapped, assemble the first connecting rod assembly (JE Piston and Scat seen here). Install double spiral clips to either end of the wrist pin to hold the rod/piston assembly securely together. Then attach the specific piston rings to the designated rod/piston assembly that’s matched to a particular cylinder. Install the connecting rod bearing, and place the oil ring on the bottom of the piston. On the big end of the connecting rod that attaches to the crankshaft, mark each rod/piston assembly for its designated cylinder. Liberally coat the assemblies with oil.
Step 21: Oil Cylinders and Install Piston Number-1
Before installing the piston/rod assemblies, give the cylinders a good oil bath by applying oil with your fingers. If you look closely, you see the number “1” scribed into the purple paint on the connecting rod end.
Step 22: Torque Connecting Rod Bolts
Before moving to piston number-2, attach the bottom of the connecting rod to the crankshaft, install the bolts, and snug the connecting rod bolts for piston/ rod assembly number-1. You may need to use a piston/rod assembly persuader tool (the metal rod with rubber ends resting on the side of the Dart engine block in this photo). With help from a persuader tool, push the number-2 piston/connecting rod assembly into number-2 cylinder. Use a piston-ring/piston-squaring alignment tool. Wielding a T-wrench, attach the connecting rod end to the forged-steel crankshaft and tighten those two bolts before moving to number-3 cylinder and 4. Repeat the installation process for cylinders/pistons number-5 through -8. Use motor oil to coat the second bank of cylinders before installing piston/rod assembly number-5 with the piston-squaring cylinder. Mere seconds after this photo was taken, QMP picked up the persuader and pressed the number-5 piston/rod assembly into cylinder number-5.
Step 23: Torque Bolts (Continued)
Finish installing the connecting rod end on piston/ rod assembly number-8 and flip the engine upside down to torque the connecting rod bolts to 60 ft-lbs in three steps: 20, 20, and 20 ft-lbs. Torque the connecting rod bolts on piston/ rod assembly number-6, and you have just two more assemblies to torque before completing this portion of the build. After torquing all the connecting rod bolts, check the side clearance of all the rods to the interior of the block. All our rods are clear by .023 to .025 inch. You now have a short block.
Step 24: Determine Lobe Center of Cam
Use the dial indicator to dial in the lobe center of the camshaft. For us that turned out to be 114 and is spot-on for this 427 Dart stroker engine.
Step 25: Install Head on Block
Before installing the heads, press-in a couple dowels to locate the cylinder heads (ours are Dart Pro CNC-aluminum high-performance). These dowels also help to align the Fel-Pro cylinder head gaskets. Different-length ARP studs are used to attach the Dart aluminum Pro-CNC cylinder heads. Install the passenger-side aluminum cylinder head first; except for the valvesprings for the number-1 cylinder. Use a dial gauge to confirm clearance between the cylinder head and the piston. You only need to check one cylinder because all the clearances are the same. That’s why the valvesprings are not installed on the first cylinder in this picture.
Step 26:Torque Cylinder Head Bolts
After the other two valvesprings are installed and the cylinder head bolts are tight, torque the head bolts to 110 ft-lbs in three steps. Do this to ensure that the cylinder heads are tightened evenly.
Step 27:Install Lifter, Pushrod and Roller Rocker
After thoroughly bathing the lifter in oil and applying assembly lube to both the cam side and the push rod end of the lifter, install the lifter, push rod, and roller rocker assembly for the number-1 cylinder. Move down the line from valvespring to valvespring and from cylinder to cylinder until the high-performance valvetrain assembly is installed. Inspect the pushrod-to-roller rocker height. If you determine that the pushrods are too long (as we did), get the correct size.
Step 28: Install Oil Pump, Oil Pickup and Windage Tray
Flip the engine upside down and install the oil pump. We learned from Melling that Dart aluminum engines are so efficient at flowing oil that a stock Melling oil pump is sufficient. If you used a high-flowing racing Melling oil pump, the top of the engine would be flooded with oil.
Step 29: Mark and Trim Oil Pan
If you discover that the pan needs a bit more massaging before it will fit, mark the inside lip of the pan where it needs to be trimmed. A pneumatic cutter makes easy work of aluminum trimming on an oil pan.
Step 30:Install Timing Set Cover
After confirming the oil pan modifications do the job, install the timing set cover.
Step 31: Install Oil Pan
In preparation for installing the oil pan, install the gaskets. There is also a half-round gasket that fits on the timing chain cover; the timing chain is underneath. Use Mr. Gasket sealer over the entire Fel-Pro oil pan gasket. Notice also that our Moroso oil-pan studs are already in place. Forming the basis of a beautiful custom powerplant from top to bottom, QMP installed our custom-aluminum Moroso oil pan on the Dart aluminum block. Torque all nuts to spec.
Step 32: Install Intake Manifold
With all the lifters installed, attach the intake manifold gaskets and carefully apply Mr. Gasket sealer on the front and rear valley wall of the engine block. Our Weiand Stealth aluminum intake manifold is installed, with all the ARP fasteners torqued to specs.
Step 33: Install Water Pump
After getting the correct-length/size Comp Cams pushrods, QMP installed them, as well as the Comp Cams roller rockers. Using two cork gaskets for the valve covers, we topped off the Dart aluminum Pro-CNC cylinder heads with Ford Racing Cobra 427 valve covers and installed the Edelbrock aluminum water pump, procured from Summit Racing.
Step 34: Install Front Accessory Pulleys
Install the pulleys on the damper (shown) and on the water pump. We selected the March Performance polished-aluminum pulley system for small- and big-block Ford V-8 engines.
Step 35: Install EFI System
The proverbial cherry on top of this exquisite powerplant is a Holley Avenger throttle-body electronic-fuel-injection system.
Step 36: Install MSD Distributor
Also at the top and even cherry red in hue, an MSD distributor is in place in this state-of-the-art Dart aluminum 427-stroker powerplant.
Mating Engine to Transmission
We acquired a Tremec T56 Magnum 6-speed manual transmission for our Dart aluminum 427 fire breather, since the T56 Magnum can handle all the horsepower and torque that our mill can throw at it. Using this transmission isn’t exactly the easy way. There’s a customizing premium to pay. But it’s the best manual transmission, so it’s in keeping with our ultimate goal.
Written by D. Brian Smith and Posted with Permission of CarTechBooks