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.
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.
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.