Interestingly, what makes these heads so good is a combination of engineering genius, and failures in the original Ford design. Borrowing architectural cues from the small-block Cleveland, Ford engineers incorporated large ports and canted valves into the 429/460 cylinder heads. With flat 15-degree valve angles, the design seemed like a winner on paper, but in reality, its performance fell far short of its promise. This, combined with the abrupt end of the muscle car era, is why 460s were installed primarily in trucks and large sedans over the years, and developed an unfavorable reputation. "The factory big-block Cobra Jet heads were a pretty good design with some fundamental design flaws. The chambers were offset too far to the outer edges of the block, so half of it was positioned outside of the block and the other half was essentially a big quench pad," Kaase explains. "As a result, the intake valve got very close to the outside of the block as it opened, which caused severe shrouding and impaired flow. When I redesigned the heads for Ford Racing in 2001, I moved the entire combustion chamber closer to the intake manifold and centrally positioned the intake valves, setting them up at an 8.5-degree angle. The new valve location significantly improves flow at low- and mid-lift."

In as-cast form, Ford Racing's Super Cobra Jet heads are capable of flowing 345 cfm, but Kaase has been able to coax over 400 cfm out of them with some skilled port work. This led to the advent of the P-51 castings, which provide comparable airflow to a set of fully ported Super Cobra Jet's in an as-cast design for the ultimate in out-of-the-box performance. "In addition to casting ports that mimicked the design of a set of fully ported SCJ heads, we revised the water jacket to allow more aggressive porting of the short-turn radius. Likewise, we reshaped the combustion chambers and touched up the bowls and the area beneath both valve seats before writing a CNC program to accurately replicate it," says Kaase. "None of this stuff is new, and we integrated design elements from various cylinder heads we've worked on-like the Yates and Cleveland heads-and incorporated them into the P-51s. One of the biggest challenges was keeping the ports in the stock locations. Raising them would have picked up flow quite a bit, but if your heads won't work with the off-the-shelf intake manifolds and headers that are out there, you're shooting yourself in the foot."

During the early stages of this project, Kaase enticed us with a proposition that seemed too good to be true: "With a set of P-51 heads and one of my custom cams, you'll make close to 800 hp." It turns out he was right. Our 532 belted out 775 hp at 6,500 rpm, and 673 lb-ft at 5,300 rpm on 93-octane pump gas. It's worth noting, however, that from a standpoint of typical magazine testing protocol, we missed the mark. In other words, we set our combination up to most accurately replicate its operating environment inside a car-like most readers would-instead of implementing some common tricks for the sole purpose of posting a big dyno number. The Hooker headers, for instance, are the exact same set of pipes we'll be running in the '93 Mustang this 532 will ultimately power. Most dyno headers don't have nearly as many bends and kinks, which can only impede flow. "On a 750hp motor, a dyno header-or a chassis header as many people call them-can easily be worth 20-25 hp compared to a production-car-style header of the exact same diameter," explains Judson. "The bends of a production header can sometimes improve low-end torque, but they'll definitely hurt the top end, especially at this power level." Furthermore, we opted for an Edelbrock water pump due to its excellent flow characteristics, and the bulletproof reliability of a mechanical pump on a street/strip motor even though an electric unit would have freed up some more ponies. The bottom line is that if dyno racing is your goal, you can certainly improve upon our build with a few simple tricks. In the meantime, we're more than content with our real-world 775 hp.

Will It Hold?
With the potential to effortlessly make such prodigious power with a big-block Ford, durability becomes a major concern. And let's face it, the big-block's smaller brethren-whether 302s or 351 Windsors-are infamous for literally splitting their blocks in half under strenuous power loads. Rest assured, big brother is more than up to the task. "You can get up to 800 hp real quick with one of these motors with nice parts and no porting. Fortunately, Ford cast the 429/460 blocks using very strong metal," Kaase explains. "We have a production-block-based 521 dyno mule in the shop that has a Scat cast crank and steel rods that's making 900 hp. Just about everything we R&D has been tested on this motor. Despite the fact that we've done nothing at all to beef up the block and it has two-bolt mains, it's still holding together after thousands of dyno pulls.