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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.
Knowing we had enough head flow to meet our goals, we turned our attention to the camshaft and intake manifold. Crane supplied a dual-pattern, solid-roller profile that offered a 0.746/0.732 lift split, a 272/280 duration split, and 114-degree LSA. Healthy by any standard, the cam was teamed with a set of roller lifters; an adjustable, billet, double-roller timing chain; and hardened pushrod all from Crane Cams. Crane also supplied the necessary 1.73-ratio, aluminum roller rockers and timing button to keep the roller cam properly located. Though available for flat-tappet and hydraulic roller applications, the Kaase heads were equipped with roller springs designed for cams up to 0.800-inch lift. Topping the heads was an Edelbrock Victor 460 intake designed to accept a 4500-series Dominator carburetor.
Feeding air and fuel to the stroker was a Holley 1150 Ultra Dominator. The word trick hardly does justice to these new carburetors from Holley, but know that the thing was nearly spot on right out of the box. We tried changing jets just because we felt guilty about not doing so, but were rewarded with changes of just a couple horsepower.
To illustrate the impressive power offered by the Kaase heads, the 557 stroker was run with an Aeromotive fuel pump, an MSD ignition system and 2.25-inch Hooker headers. Filled first with Lucas break-in oil and a bottle of (high-zinc) break-in additive, the Milodon pan was eventually filled with 5W-30 synthetic for the power runs.
After a pair of break-in cycles and some timing sweeps, the 557 eventually spit out 754 hp at 6,300 rpm and 713 lb-ft of torque at 4,700 rpm. Remember, this was with a static compression ratio below 10.5:1 and a simple oiling system (meaning no windage tray). We noticed the big motor was very sensitive to oil level and having too much oil limited power. In fact, the power climbed each time we drained a quart out until we started to get a drop in oil pressure. What this motor really needed was a windage tray—our fault, not Milodon's, as it only supplied what we asked for.
Satisfied with our normally aspirated power, we added a small shot of nitrous. NOS supplied an adjustable Cheater (plate) system designed for our 4500-series Holley Dominator. Adjustable from 150hp to 250hp, the system was perfectly suited for our street-strip application.
Math told us the 750hp 557 stroker would require the full 250hp shot offered by the kit, so we started with 200hp jetting. After installing the solenoids on a billet Wilson nitrous plate, we made sure to elevate the internal pressure to just over 1,000 psi (bottle temp at 92 degrees).
After minor adjustments to the independent fuel pressure supplied to the nitrous solenoid, the NOS-fed 557 responded with peak numbers of 1,014 hp and 935 lb-ft of torque. Imagine having 1,000 hp at your fingertips after swapping this fire-breather into a light Fox Mustang?
BBF Head Flow Comparison
|Super Cobra Jet||Kaase P51|
Kaase P-51 Cylinder Head Specs
|Intake runner volume||310 cc|
|Exhaust port volume||145 cc|
|Intake valve diameter||2.250 inches|
|Exhaust valve diameter||1.760 inches|