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To further enhance the power...
To further enhance the power production of the five upgrades we added in Part 1, a set of AFR Magnum 305 heads was chosen to top off the 454. Here, Joey D's 55 Bel Air (the No-Jive-Five-Five) is strapped down on SLP's dyno to see what the heads are worth.
We add a set of AFR 305 heads to our 454 to complete its transformation into a 21st-century big-block.
Last month, we tested five different key components to update an old-school 454 Rat in Joey Diorio's '55 Chevy. Once we changed from the old-tech hot rod parts to the five new pieces, we realized a total gain of 73 hp and 87 lb-ft of torque to the rear wheels.
These were not off-the-wall, pie-in-the-sky parts, just the latest off-the-shelf components from the aftermarket. We did this to illustrate how much more horsepower may be lurking in your prehistoric big-block. The first of the five changes was replacing the 20-year-old-design hydraulic flat-tappet cam with a new Lunati Voodoo solid street roller. The gains were such that the old 750 Holley double-pumper was no longer up to the task of feeding the 454. We ditched it for a new Holley 950 HP carburetor.
These aluminum AFR cylinder...
These aluminum AFR cylinder heads (as-cast Magnum 305s) will improve airflow, power, driveability, and efficiency over the old iron castings. We upgraded to roller springs (250 pounds closed, 600 pounds open) with titanium retainers. Standard equipment includes ARP rocker studs and guideplates to top off these beauties.
Going from the stock 14 volts to 18 volts of ignition power using Performance Distributors' Mini VIP gave us another 7 hp and 4 ft-lb. Switching to a Wilson Manifolds four-hole tapered carb spacer in place of a plain four-hole spacer gave us four more ponies. The last swap was getting rid of the '70s-era Weiand Team G single-plane intake for a recently redesigned version (plus 14 hp and 7 ft-lb). These five alterations also dropped the '55's e.t. by more than a second on the strip.
Today's street engines often make more power per cubic inch than '60s and '70s race engines. This is due to the technically advanced designs and manufacturing of today's automotive components. The next step to complement the aforementioned changes was swapping on a set of state-of-the-art cylinder heads. Recent offerings in cylinder heads just blow away those of yesteryear, even if those old castings received a thorough porting job by an experienced and skilled technician.
Our choice for this upgrade was a set of Airflow Research's aluminum 305cc Magnum heads. The 454's stock iron castings were the good (back in the day), high-performance, rectangular port heads. The stock rectangular port castings may have larger intake runners (315-320cc), but they offer less airflow than the AFR's smaller 305cc runners. The AFR 305s provide maximum airflow with minimum port volume for added velocity. A smaller port that flows more air is better for driveability (part-throttle response) and power production throughout the rpm range. These AFR heads demonstrated huge flow improvements at every lift value, not just at peak.
Goin' Flowin'
After receiving the AFRs at our Jersey office, we brought them to SLP Engineering in Toms River, New Jersey, for flow bench testing. We had a pair of ported rectangular port heads on hand to flow-test against the AFRs. After Joey D removed the bone-stock heads from his '55, we benefited from a three-way head-flow shootout. The AFR's average airflow numbers from .200- to .700-inch lift were 48 cfm more than the stock rectangular port heads and 44 cfm more than the ported heads. At .500-inch lift the as-cast AFR 305s produced 62 cfm more airflow than the stock castings and 54 more cfm than the ported units. (See the flow charts on page 92.) AFR now has 315 CNC-ported BBC heads that offer even more airflow gains than the tested as-cast 305s.
The AFRs are stock replacement heads with a few considerations. You'll need longer pushrods and 1-inch-longer head bolts for the four bottom exhaust boltholes. The exhaust ports are raised W-inch, which can cause header clearance issues (like on our Tri-Five with the "605" power steering box). We tried 2-inch headers made to fit a stock BBC in a Tri-Five, but they ended up hitting the block and the transmission bellhousing area. Ironically, we had to reuse the old '80s Blackjack 1 Y-inch headers that fit snugly next to the "605" steering box. For our new combination we should have been able to use 2- or 2 V-inch headers for the new, better-breathing heads. Had we been able to find such headers that fit with the power steering (Joey didn't want to do any cutting on the '55), we would have seen even more dramatic results.
 The heart-shaped CNC chamber...  The heart-shaped CNC chamber measured 119cc before optional angle milling brought ours to 112cc. The fully CNC-machined chamber enhances flow while creating a faster, more efficient combustion for added power. Looking at these castings side by side, the iron unit (left) shows its outdated and less efficient 118cc combustion chamber with 2.19/1.88 valves. The aluminum piece sports its modern and effective CNC chamber with 2.25/1.88 valves. |  Here's a look at the 9:1 454...  Here's a look at the 9:1 454 Rat/mule motor with the antiquated iron heads removed while awaiting its new aluminum units. This '70s replacement/crate motor has been serving well for more than 20 years. |  |
 Most gearheads are familiar...  Most gearheads are familiar with the '60s/'70s BBC head castings. When a BBC head displays "HIGH-PERF," it'll have rectangular ports, while castings with the "PASS" designation will have oval ports. The 990 castings (like this one fresh off the Rat) were equipped on the hundreds of 454 crate motors sold back in the 1970s and 1980s. |  Both the iron (bottom) and...  Both the iron (bottom) and aluminum casts are obviously rectangular port BBC heads. The stock iron castings typically have 320cc intake runners. The smaller 305cc AFRs have higher air velocity with much better flow. AFR has done lots of R&D to design its heads with a smaller port volume, better port shape, combustion chamber, and a special five-angle valve job to produce a desirable head package. |  Looking closely at the deck...  Looking closely at the deck of both heads, it's noticeable the new castings have a thicker deck surface with raised (W-inch) exhaust ports. The raised ports flow better to produce more power but can cause header clearance issues. Be sure to purchase the appropriate headers for these recent offerings with their raised exhaust ports. |