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Kaase P-51 Heads on a 1,014HP Basic Big-Block
We use Kaase P-51 heads and a 557-inch stroker to make big, reliable street/strip power.
When it comes to making power, there is one simple rule of thumb—bigger is better! Generally, if a 302 is good, then a 347 is even better. By the same reasoning, if a small-block is good, then a big-block must be … well, you get the idea.
The science behind the bigger is better is actually sound—for each revolution, bigger motors take a bigger gulp of air, they can burn more fuel and then pump out a commensurate level of power. Not only do they make more power, but usually do so at a lower engine speed, thereby increasing longevity.
Engine speed and reliability are inversely proportional, so having to make peak power at high rpm can decrease engine life. The reliability factor can be offset with cubic dollars, but big motors are both cheap and powerful, and that's just what most enthusiasts are looking for.
In truth, Ford offered two distinct big-block engine families, starting with the FE. The famous 428 Cobra Jet and 427 Side-Oiler FE motors were legendary thanks to Thunderbolts and Mr. Shelby, but the focus of this article is the other (bigger) big-block, the venerable 460.
The biggest standard displacement offered by the Big Three (Chevy, Ford and Dodge), the 460 Ford never saw performance duty and was instead relegated to heavy passenger car and truck applications. The 460's little brother, the smaller 429 was called into service for high- performance models, but for our needs, it doesn't matter where you start, as long as you end up going big.
In addition to its pedestrian status, the 460 was actually limited (in outright performance) by head flow. Despite the (successful) Cleveland-style, canted-valve arrangement, the factory big-block heads never delivered on their performance promise. Instead, big-block owners looked to the aftermarket for solutions, which eventually came in the form of the Kaase-designed Ford Racing Cobra Jet and Super Cobra Jet heads.
The Cobra Jet heads represented a performance step above the factory casting and the Super Cobra Jet heads a step above the standard versions. Despite the significant upgrades offered by the Cobra Jet family, big-block Fords were still limited by head flow—that is until Kaase stepped up and introduced the P-51 heads.
Advertised as the best Cobra Jet-style heads on the market, specs for the P-51 heads include 310cc intake ports and 147cc exhaust ports. The altered (from stock) valve angles carry heavy-breathing, 2.25-inch intake and 1.76-inch exhaust valves.
Port-wise, the P-51 heads were a step up (in as-cast form) from what might be expected of a professionally ported set of Super Cobra Jet heads. The flow numbers indicate that 400 cfm comes at just 0.700-inch lift, meaning there is a meaty curve in the lower lift ranges.
Always the limitation of the BBF head, the exhaust flow of the P-51 head checked in at 251 cfm thanks to machined and hand-blended port throats below the valves. A portion of the power production offered by the Kaase heads can be attributed to the CNC combustion chambers, which greatly reduce the dead area behind the spark plug.
With so much promised power, we couldn't help but take Kaase up on his offer to run a set on the dyno. For this test, we were torn between limiting the power of the motor and the expense of building an all-out race beast. In the end, we decided to build a hot street/strip motor capable of running on pump gas. To up the ante for serious race use, we also employed a taste of giggle gas to keep things interesting.
The only thing better than a 700hp normally aspirated street stroker is one that makes 1,000 hp on the juice. To that end, we enlisted several manufacturers to help us build a suitable test mule. Starting with a 460 block machined and bored 0.080-over by L&R Automotive, the BBF received a 4.50-inch stroker crank and rods from Procomp Electronics, and a set of forged (dished) pistons from Probe Racing. The 33cc dish combined with the 557-inch displacement and 72cc chambers heads to produce a pump-gas-friendly static compression ratio of 10.46:1. The balanced combination also relied on Total Seal rings, ARP head studs, and Fel Pro head gaskets.