Jim Smart
September 17, 2012

When Ford was developing and racing its legendary 427 FE big-blocks back in the 1960s, it endured a tremendous learning curve that was proven out in dynamometer laboratories and racing venues worldwide. It was never easy for Ford to achieve this greatness because nothing worthwhile--especially in racing--has ever been easy. Burning the midnight oil, breaking prototype parts, and financing expenses are all key requirements for success. All of this was spurred by Henry Ford II's desire to hand Enzo Ferrari his jewels at Le Mans, the world's biggest motor racing stage. Not only did Ford do it once, it did it three consecutive times with exotic Ford GT40s. Ford proved it was dominant, global, and a force to be reckoned with.

The man that made Ford's will a reality, Carroll Shelby, is the subject of many stories and folklore. Prior to his involvement in the GT40 program, Carroll Shelby's objective was to design and build the world's fastest sports car--and he did in 1965. The 427ci Cobra went from 0 to 60 mph in 4.2 seconds, 0 to 100 mph in 10.2 seconds, and had a top speed of 160 mph. It tipped the scales at 2,350 pounds with more than 500 horsepower on tap. Shelby's 427-powered Cobra held the crown of world's fastest production car (0-100-0 mph in 13.2 seconds) for more than 30 years before Ferrari caught up and passed the Cobra a few years back. In competition dress, the Cobra was a Ferrari-spanking 580-horse powerhouse using real American V-8 twist. It was this formidable powerplant that Shelby also shoehorned into the GT40 Mark II to make it the race-winning machine that it eventually became.

Before you are two such 427s. One is vintage Cobra specification and the other a 482ci stroker. Both are custom built for McCluskey Limited of Torrance, California--known for its extraordinary Cobra rocket ships. The objective was to build and test a '66 Cobra specification 427 and wring it out on the dyno to see how it would perform. Aside from the rare C5AE-H Medium Riser aluminum “X” heads, magnesium intake manifold, and a 780-cfm competition Holley with Le Mans bowls, this is a period piece from the 1960s. We're talking aggressive flat tappet cam technology from Comp Cams and a stock Ford dual-point ignition with MSD assistance.

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Entrusted with the vintage hardware were Jim Grubbs and Jeff Latimer of JGM Performance Engineering. Both employ a wealth of engine building and tuning experience between them, which made it straightforward to build two 427 FE powerhouses that would leave indelible marks in the JGM dyno record books.

We actually kicked off this build in last month's issue, introducing the two-engine comparison. Block 1 was a genuine SOHC block with a casting number of C6AE-B, which doesn't mean “SOHC” but certainly a 427 side-oiler. What made it an SOHC block were the 5?8-inch oil drain holes at the rear of each deck, which got our Ford Blue blood pumping. Block 2 was a genuine vintage Cobra block with the original Shelby CSX VIN stamped in its iron. While Block 1 would be built, dyno tested, and placed on static display. Block 2 would be stroked to 482ci and raced in a Cobra Daytona Coupe.

There are elements that make the 427 side-oiler different than center/top-oilers. What stumped Latimer was the presence of a pressure relief valve in the block and in the high-volume oil pump. Strike up a conversation in any FE crowd and you will get a variety of opinions on what to do about oil pressure control in the side-oiler. Originally, the 427 side-oiler didn't have an oil pressure relief valve in the pump, but rather had one in the back of the block. JGM opted to remove the oil pump's relief valve, much as Ford did to begin with, and go with the side-oiler's gallery relief valve.

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What we learn from both of these engines is what's possible from original equipment Ford castings, and it gives us a strong sense of what Ford engineers faced a half century ago. Though we have rare and desirable parts among these beasty 427s, imagine what they could do with better cylinder heads and induction. Ford's own 427 High Riser heads and induction would be a good start, though you'd lose torque on the low end.

The aftermarket offers a wealth of great cylinder heads and induction systems for the FE depending on your expectations and budget. Because these 427s had to be assembled as original-appearing FE mills utlizing factory castings, they suffer from the limitations of Medium Riser dimensions (2.18-/1.72-inch valves with 2.78x1.38-inch intake and 1.78x1.30-inch exhaust ports. With these heads, you get good low to mid-range torque, but not the full potential on the high end because they are basically a street/race head. The aluminum "XE" advantage isn't so much breathing, but instead great heat sink capability to where you can run a pinch more timing, higher compression, and a slightly leaner mixture depending upon what you get for a plug reading. This is where dyno time is money well spent before placing your FE between the shock towers. But that is another story. Check out the captions to see just how these two vintage V-8s faired in the dyno cell.

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Two FEs--One Polygraph Room

This was an opportunity to dress a 427 up in its original clothing void of special modifications--basically Ford's legendary Cobra FE 427 as it was in the mid-1960s when it powered the world's fastest production automobile. We wound up with 510 hp and 503 lb-ft of torque. This is what JGM got from a basically stock 427 FE with rare metal on top. Horsepower and torque numbers aren't much different than you would have seen in 1966, and the gains aren't all that significant with the aluminum heads and magnesium intake. Aluminum heads allow us to run more timing and less jetting in an effort to gain power. Further gains could have been achieved with a more aggressive roller mechanical camshaft, larger carburetor, and richer jetting. Jim and Jeff followed instinct and went with what they knew works. Here are some of the more significant pieces JGM specified for this circa '66 427.

JE custom forged pistons with race ring set(No Part Numbers)
ARP connecting rod bolts200-6001
Fel-Pro gaskets and seals throughout
Comp Cams flat tappet mechanical camshaft custom grind33-000-5
Comp Cams valvesprings972-16
Comp Cams lifters810-16
Sealed power rocker shaftRS-621
Pro-Gear high-performance timing setPG4108
Melling high-volume oil pumpM-57HV
ARP oil pump shaft154-7902
AMK Products cylinder head bolt kitF-1771
AMK Products engine bolt kit660-427HP
C5AE-H experimental aluminum heads2.18/1.72-inch intake/exhaust
C6AE-J 427 side-oiler block with SOHC drain holes
Magnesium dual-plane medium riser inductionNo Part Number
"XE132391" steel crankshaft with Welsh oil galley plugs and C-clips
C6AE-E cap-screw connecting rods with ARP boltsalso 428 SCJ

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Two FEs--One Polygraph Room

Sister Block 2 with 4.155-inches of stroke, an 830-cfm Holley, and an aggressive Comp Cams roller mechanical cam delivered 131 more horsepower and 105 more lb-ft of torque. Like Block 1, Jim and Jeff took what they knew worked and applied it to the 482 to get the 641 hp and 608 lb-ft of torque. There are always ways to make more power--more cam, a larger carb, advanced timing, richer jetting, and bigger heads--but you also want durability from your FE or all the power in the world won't make any difference. It's always a compromise between power and durability--an engine that will finish the race. Stroking the large-bore 427 to 482 ci gives this mill deep lungs and more torque. This is what 4.155 inches of stroke from a Crower billet crank will do for the 427 block. Here's what's inside.

Crower steel billet crank95191C
Manley steel H-beam rods14072-8
ARP 2000 rod bolts
Comp Cams custom roller camshaft33-000-9
Comp Cams roller mechanical lifters839-16
Comp Cams push rods8470-16
Comp Cams valvesprings927-16
Melling high-volume oil pumpM-57HV
ARP oil pump shaft154-7902
C5AE-H experimental aluminum heads 2.18-/1.72-inch Intake/exhaust)
T&D rocker shaft assembly7021
Mallory distributor Pertronix Ignitor conversionML-181
Holley HP, 830-cfm carburetor0-80509-1
1-Inch carb spacerR9136

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18 JGM Performance Engineering runs 30-weight Joe Gibbs BR30 break-in oil on all dyno tests. BR30 has the right additives for streamlined break-in including flat-tappet cams.