How to: Build a 429 Super Cobra Jet
We get 467 horsepower from an iron-head 385-series-big-block
At 375 horsepower and 450 lb-ft of torque, the 385-series 429ci big-block was the most powerful factory engine ever installed in a first generation Mustang. Ford initially used the short-block with hemi heads in '69 to conceive the limited production Boss 429 Mustang. However, the Boss 429 was not for everyone. For '71, the 429 got wedge heads for two forms of Mustang rocket propulsion—Cobra Jet and Super Cobra Jet.
The 385-series big-block was Ford's response to Chevrolet's 396, 427, and 454ci big-blocks, conceived to replace the FE-series 390, 427, and 428ci big-blocks along with the heavy and outdated 462ci MEL (Mercury, Edsel, Lincoln) V-8 in 1968. The 429 and 460ci big-blocks were a new generation of large-cube engines developed for both luxury and performance. They employed a lightweight casting technique with a no-skirt block and made huge power with poly-angle valve heads.
The '71 429 Cobra Jet hit the option sheet with an aggressive flat-tappet hydraulic cam, stamped bolt/fulcrum rockers, 715-cfm Rochester Quadrajet carburetion, dual-plane "spread-bore" iron manifold, four-bolt main block, and large-port cylinder heads to make a factory rated 370 horsepower and 450 lb-ft of torque. You might ask why Ford looked to General Motors for a carburetor when it had the Autolite 4300 and 4300D available. It boiled down to tougher emission standards and the absence of a large enough Autolite four-barrel for a 429 Cobra Jet.
The mechanical lifter 429 Super Cobra Jet was the second punch response to Chevrolet's 450-horse 454ci LS6 big-block. It added an aggressive mechanical cam, adjustable stud rockers, and 4150 Holley carburetion. Like the big Chevy, Ford's 429 SCJ was underrated at 375 horsepower. According to Ford insiders, the goal was to take this engine to 500-plus cubic-inches had the battle for street dominance not ended in 1970. Detroit turned down the wick when focus shifted from racing and performance to safety, emissions, and fuel economy.
There are few things Jim Grubbs of JGM Performance Engineering loves more than 385-series 429/460ci big-blocks. They make big low- and mid-range torque for luxury cars and trucks, plus they can be dialed in for horsepower in a Mustang. Jim wanted to know how much power could be made from a 429 Super Cobra Jet with factory iron heads and intake along with a stock Crane flat-tappet hydraulic camshaft.
Grubbs has always known the great potential of Ford's 385-series big-block and has collected a treasure trove of big-block Ford parts through the years. In his arsenal was a 429 Cobra Jet block with four-bolt mains, thick webs, 4.360-inch bores, and 10.310-inch deck height. He also had 429 Cobra Jet heads with 2.19/1.73-inch intake/exhaust valves, 72-74cc chambers, and adjustable valvetrain. Also on the shelves was a 4UA iron crank with 3.590-inch stroke along with a set of D0OE-A forged steel Cobra Jet rods.
All Jim needed were Speed Pro forged aluminum .030-inch oversize pistons, bearings, rings, and Fel-Pro gaskets to get started. Crane provided a stock flat-tappet hydraulic cam, while Comp Cams set him up with hydraulic lifters equipped with tiny .012-inch oil holes designed to keep lobes lubricated. Speed Pro provided stainless steel replacement 2.19/1.73-inch valves. With a little head port massaging, Grubbs achieved 467 horsepower and 480 lb-ft of torque.
Cobra Jet Block
The 429 Cobra Jet block (Ford part number D0OE-B) was a limited-production block casting with four-bolt mains, thicker main webs and cylinder walls, and a "CJ" cast in the lifter valley. Expect to see a D0VE-A or D1VE-AA casting number. There is also a 460 truck block with a D7TE or D8TE casting number also machined for four-bolt mains. It has 4.360-inch bore just like the 429 CJ/SCJ block. Unless you are concerned with a matching number block, the 460 truck casting is a drop-in replacement. Another consideration is being able to convert any 429/460 block to four-bolt mains because there's plenty of web thickness to get the job done if you have four-bolt main caps.
No Worries Over Zinc
Recently, there has been concern about the removal of zinc and other additives from engine oil because they are believed to harm the catalytic converters in newer vehicles. By eliminating these additives, a new challenge has been created for classic car owners—excessive flat tappet cam lobe wear and failure. Comp Cams has chosen to do something about this problem in its #1590-12 Engine Break-In Oil with ZDDP enhancement, which provides protection for moving parts during the critical first firing and break-in period. Because JGM is running a traditional flat-tappet camshaft, protection is important so Grubbs poured seven quarts of 10W30 weight Comp Cams Engine Break-In Oil in the pan to help get this SCJ off to a good start. Comp Engine Break-In Oil is available in 10W30 and 15W50.
Cobra Jet Induction
Ford's 429 was fitted with two basic four-barrel intake manifolds—D0OE-9425-D designed for a spread-bore carburetor (four-barrel and Cobra Jet) and D0OE-9425-C for the Holley 4150/4160 square flange (Super Cobra Jet). Both are cast-iron and weigh as much as a bank vault. There is also a variety of great aftermarket manifolds, both vintage and contemporary, that perform very well. If you are going for raw high rpm horsepower, you want a deep breathing single-plane manifold. For the street, a dual-plane manifold yields a broad torque curve that begins to come on strong at 2,000 rpm and pulls like stink through 5,500.
You won't see a Ford part or engineering number on a Ford Quadrajet. According to the Ford Carburetor Guide by Pony Carburetors and the late Jon Enyeart, there are four numbers that apply only to Ford Quadrajets—7040285, 7040286, 7040287, or 7040288. If it doesn't have one of these numbers, it is not a Ford Quadrajet. The 429 is the only Ford engine ever fitted with a Quadrajet.
SCJ Truth Telling
How is it possible that an engine factory rated at 375hp, 450 lb-ft of torque can make so much power (nearly 100 horsepower and 30 lb-ft more!) on JGM's Superflow 901? Much of it boils down to blueprinting, dynamic balancing, head porting, a Holley 750-cfm HP carburetor, PerTronix distributor with Ignitor II, and precision tuning. On the dyno, the JGM 429 SCJ exhibited a broad torque curve and real horsepower on the high end considering this is an iron stocker with a stock spec cam.
There are two points to consider here. One, factory horsepower and torque numbers aren't always true, typically founded under controlled conditions. Detroit automakers had to lower published horsepower and torque numbers due to insurance rates, especially for younger drivers. In truth, the 429 SCJ produced more like 425-450 horsepower and 480 lb-ft of torque, more on a par with the big-block Chevy. These numbers demonstrate what you can do with a 429 SCJ stocker. Imagine what this thing would do with aftermarket heads and induction along with a hot mechanical roller cam.