Of the domestic big-block engines, the 429/460 Ford 385-Series came to the party late in the game. Ford depended on the ancient but effective FE-series of engines for big-inch power through most of the '60s musclecar era, introducing the all-new big-block design in 1969. This new fat-block had commendable features, including a wide 4.900-inch bore spacing for man-sized bores, a healthy 10.320-inch deck height, and a spacious crankcase to swallow a burly long-stroke crank. Up top, the engine featured a canted-valve layout and huge ports, borrowing design themes from the famously successful Cleveland small-block series. It seemed like a design with tremendous power potential, and in Cobra Jet and Super Cobra Jet 429 form, the power output was noticeable (with rated outputs of 370 and 375, respectively). Ford's Total Performance attitude didn't stop there, either. Looking for the ultimate weapon in the NASCAR wars, the Boss 429 was created in 1969, and featured a radical canted-valve semi-Hemi cylinder head layout with the intention of fully exploiting the new big-block's power potential.
Ford's reasoning was well directed with the Boss 429. But for all the positive attributes of the Ford's big-block architecture, and given the promise of power offered by the base canted-valve heads and cavernous ports, the ultimate power available from the new design just didn't cut it. Ford's solution was a radical departure in the cylinder head layout-but why? Though the conventional 385-Series heads seemed like a conceptual winner, there were flawed design elements clear in retrospect. Foremost, the valve placement put the centerline of the valve faces too far toward the plug side of the chamber, crowding the outside of the cylinder bore. Combined with the valve angle, this layout did nothing to take advantage of the naturally spacious bores of the bottom end. The problem is readily evident on the intake side, and is especially acute with the exhaust valve, buried deep within the curvature of the bore's outside corner.
From the standpoint of taking advantage of airflow for maximum power, the conventional 429 and 460 cylinder head was a loser, but this shortcoming became inconsequential as the era of maximum factory performance drew to a close. The big-block Ford 429 and its longer-stroke brother, the 460, came to serve primarily as torquey powerplants in huge Ford, Lincoln, and Mercury luxury cars (and as a truck motor). So much promise seemingly squandered.
The Fix Is In
In the '80s, Ford Motorsport (now Ford Racing) took a step forward in the power evolution of the big-block, introducing the aluminum Cobra Jet head. Borrowing its name from the high-performance big-block designation of the '60s, the Cobra Jet head was a conventional 385-Series in layout, but featured better ports and greater airflow when compared to OEM production heads. Although the Cobra Jet heads were an improvement, the fundamental shortcomings of the original design layout had not been addressed. All of that changed with the introduction of the Ford Motorsports Super Cobra Jet heads in 2001.
Under development at Jon Kaase Racing, this new design finally fixed the basic flaws in the original Ford design. Kaase pulled the valves back toward the intake side of the chamber, where they could open in a more geometrically favorable position in relation to the cylinder bore. Along with the dramatic change in valve position, the valve angle was altered slightly on the intake side and drastically on the exhaust side. This new Kaase layout unlocked the power potential of the big-block Ford, and the modified version of the conventional big-block Ford layout was now capable of exceeding the 350-cfm peak intake flow of the exotic Boss 429. It was really a validation of the original canted-valve wedge concept.
The P51
Not content to remain idle, Kaase recently went to work to revise the big-block Ford head once again. This effort builds on the format originally introduced with the Super Cobra Jet head, as it is more evolutionary than revolutionary. Naturally, the Super Cobra Jet head has benefited from six years of development since its introduction, and its as-cast potential was just the beginning, in terms of power and flow. Fully ported, the Super Cobra Jet head was capable of high 300s on the intake flow scale. With the P51, the idea was to incorporate the gains made in port development on the Super Cobra Jet into an all new casting; essentially, the P51 was to be an "as-cast" piece designed to resemble the ports of a fully ported Super Cobra Jet. Material has been added and improvements made to address issues from the previous series of cylinder heads. Along with the revised ports, the P51 takes the combustion chamber to the latest figure-eight shape, filling in a considerable portion of the "dead" area behind the spark plug.
Kaase's new P51 head features a fully CNC-machined chamber, measuring the same 72 cc as the previous generation cylinder head. Other than the redesigned 310cc intake ports, the intake valve diameter has been increased from the earlier head's 2.200 inches to 2.250 inches. The exhaust ports measure 145 cc and carry 1.76-inch diameter valves, and the port throats below the valves come machined and hand-blended (though the remainder of the port comes strictly as-cast). With intake flow of around 400 cfm and an extraordinarily fat flow curve throughout the range (see flow chart), these heads seem to have what it takes to make outrageous power.
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A peek inside the bottom end of this basic 460 short-block shows a distinct lack of the exotic. Factory cast-iron abounds, as witnessed by the factory iron crank, block, and main caps. There is plenty of room inside one of these big-block Ford crankcases for enormous strokes. |
A concession to upgraded equipment in the basic short-block is a Kaase high-volume oil pump. When running nearly 400 cfm and plenty of camshaft on 466 actual cubes, high revs come with the territory, and improved oiling is cheap insurance. |
Along the same line of reasoning, a premium oil pan with increased capacity and improved oil control becomes a necessity for high-rpm longevity. A Moroso deep-sump pan with an integral screen-type windage control system meets this requirement. |
Factory rods for the 460 are forgings, and have proven durable (though an upgrade to aftermarket rods would provide an extra measure of durability). Mated to the rods are Probe flat-top forged pistons, which provide a compression ratio around 11.9:1. Note the dual-intake valve notches. These pistons will accept either the stock valve location, or the revised location of the Super Cobra Jet/P51 heads. |
These off-the-shelf Probe pistons accept OEM-sized 5/64-inch compression rings, and are floated to the rods by having the rods bushed for floating pins. Double spirolox retain the pistons to the rods. |
Installed in the block and rotated to TDC, it is evident that this piston combination yields a zero-deck short-block, providing the ideal 0.040-inch quench clearance when combined with a Fel-Pro gasket. The beefy ARP cylinder head studs apply additional clamping, a welcome aid with only four fasteners available per cylinder on the big-block Ford. |
Kaase did not shrink in modesty when spec'ing the cam profile for this engine. The custom COMP solid roller 'shaft features 256/262 degrees duration at 0.050, and delivers 0.761/0.743-inch lift with the COMP Pro Magnum 1.73:1 ratio rockers. Longer-than-stock pushrods are required with both the P51 and Super Cobra Jet (SCJ) heads. |
A pair of Kaase's new P51 heads serve as the real secret to this Ford's outstanding power output. A refinement of the concept Kaase developed with the Ford Motorsports SCJ head, the P51 sets a new standard. |
It's clear that there has been substantial development in the P51 chamber. The chamber form is a flow-enhancing, fully sculptured bowl radiating from each valve face, and the surface is CNC-machined. |