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AFR's Big-Block Ford Cylinder Heads

Dropping The Blue Oval Hammer

By Stephen Kim, Photography by Stephen Kim

Port Geometry

From the outside, the most dramatic difference between AFR's new cylinder head and the factory Cobra Jet casting are its rectangular intake ports. Technically speaking, their rounded corners could qualify them as oval ports, but, compared to the factory ports, they're very squared-off indeed. Nevertheless, according to AFR, the stock egg-shaped ports are very inefficient by nature and don't move enough air to warrant their cross-sectional area. "The factory-style Cobra Jet ports are a huge waste of space. Due to their inefficient shape and improper sizing, there simply isn't much air speed and inertia in the ports, and that kills any potential responsiveness in the engine," Mamo said. "A lazy port design with low air speed creates a pretty lazy power curve. Dramatically increasing port velocity will increase power and torque through the entire curve, in addition to improving throttle response, air speed inertia, cylinder filling, and fuel efficiency. The result is high-rpm horsepower with no compromises in part-throttle snappiness and low- and mid-range torque."

While AFR's revised port shape represents a dramatic departure from the factory Cobra Jet port geometry, rectangle ports are nothing new in the big-block Ford camp. Make that the super-high-end, big-block Ford camp. The cold, hard truth is that Ford's best Pro Stock heads since the 500ci era began—whether they're A460, B460, C460, D460, or E460 castings—all utilize rectangular intake ports, which validates the merit of the design. AFR is now incorporating this race-inspired technology in a true bolt-on street package that's 100 percent compatible with standard big-block Ford bore diameters, rocker arms, and headers. Of course, AFR's revised intake ports will require a new intake manifold, but the company is also developing an all-new cast intake manifold designed specifically for its cylinder heads.

Rat-Stomping Airflow

Getting 400-plus cfm of airflow out of a 270cc intake port is plenty impressive, but to put things in perspective, let's compare them to AFR's big-block Chevy castings.

Since the popular hot rodder method of comparing different types of cylinder heads (i.e. BBF versus BBC) based on intake runner volume is pointless, we focused on cross-sectional area instead. According to Mamo, the new 270cc big-block Ford heads have a cross-sectional area that's most comparable to the company's 300- and 315cc big-block Chevy castings. As the flow-comparison chart reveals (page 36), the Ford head has the Chevy competition handily covered on the intake side by 16 cfm. Furthermore, it's not until stepping up to AFR's 335cc big-block Chevy heads that the Bow Tie brigade catches up to AFR's new big-block Ford casting. Making the feat even more impressive is the fact that the Ford heads were flow-bench tested using a 4.390-inch bore fixture, which is rather small considering the 429/460's standard bore diameter of 4.360 inches.

These are some seriously mean cylinder heads, and with roughly 400 cfm of airflow on tap from AFR's entry-level offering, they can easily support 750–775 hp in a pump-gas application. If AFR is able to hit its goal of 420-plus cfm from its 300cc casting, then 800–850 hp is well within reach for aggressive pump-gas combos and 950-plus isn't out the realm of possibility for a 15.5:1 race-gas motor. That's not too shabby for out-of-the-box, bolt-in-and-go, street/strip heads. It's worth noting that these are preliminary airflow figures gathered from pre-production cylinder heads, but we know from experience that AFR tends to be conservative with its airflow figures.

AFR's new big-block Ford cylinder heads are tentatively scheduled to be on sale by the time your read this. Once the first batch of production heads have been cast, stay tuned to Car Craft for an exclusive first flow-bench and dyno test.

Flow Comparison (cfm at 28 inches)

AFR BBF 270 cc AFR BBC 315 cc AFR BBC 335 cc
Valve Lift Intake Exhaust Intake Exhaust Intake Exhaust
0.200 171 139 169 148 164 142
0.300 245 156 249 187 240 193
0.400 311 225 312 238 304 244
0.500 356 253 353 271 352 278
0.600 392 272 380 296 385 310
0.700 402 279 386 310 404 321

By The Numbers

AFR BBF Head Specs 270 cc 280 cc 305 cc
Intake valve diameter 2.250 in 2.250 in 2.300 in
Exhaust valve diameter 1.760 in 1.760 in 1.760 in
Valvespring diameter 1.550 in 1.550 in 1.550 in
Combustion chambers 75/88 cc 75/88 cc 75/88 cc
Intake valve angle 14 degrees 14 degrees 14 degrees
MSRP (pair) $2,099 $2,599 $2,799


One of the oldest tricks in the book for inflating airflow numbers is using an unusually large bore fixture on the flow bench. To keep its figures honest and realistic, AFR flow tested these heads on a 4.390-inch fixture. Considering that the standard bore on a 429/460 block is 4.360-inch, AFR's test procedure is about as realistic as you can get. Likewise, a test pipe bolted to the exhaust ports keeps the exhaust flow figures as accurate as possible.

To streamline the R&D process, AFR mocked up 3-D prototypes of its new 429/460 intake manifold. The single-plane design isn't much taller than current aftermarket offerings in order to preserve hood clearance, but it still has plenty of plenum volume to feed big-cube motors at high rpm.

In an effort to reduce the disparity in airflow between the inner and outer cylinders, the new manifold features an elongated plenum design. This increases the length of the center runners, while decreasing the length of the outer runners.

With prices starting at $2,099, AFR's big-block Ford cylinder heads will be one of the most affordable 429/460 options on the market. AFR hopes to have them available to the public by the time you read this.

SOURCES
Air Flow Research
28611 W. Industry Drive
Valencia
CA  91355
661-257-8124
http://www.airflowresearch.com
By Stephen Kim
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