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Turning a 1955 Chevy Into a Modern Hotrod - No Jive For Your '55

Dan Foley Apr 1, 2008
Sucp_0804_02_z 1955_chevy_modern_hotrod Power_production 2/19

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.

Sucp_0804_04_z 1955_chevy_modern_hotrod Afr_cylinder_heads 3/19

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.

Sucp_0804_06_z 1955_chevy_modern_hotrod Combustion_chamber 4/19

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.

Sucp_0804_16_z 1955_chevy_modern_hotrod Superflow_flow_bench 11/19

On SLP's SF-1020 SuperFlow flow bench, the AFRs, stock 990s, and ported 291s went head-to-head in a flow comparison test. The iron and aluminum heads were flowed with a realistic bore size fixture of 4.280-inch (typical 427 or 454, .030 over). Most BBC heads are flowed using a 4.600 bore. A larger bore unshrouds the valves to help show better flow numbers. Surprisingly, our flow bench results (with the smaller bore) were similar at the lower (.200-.400-inch) lifts but not as much at high lifts (.500-.700-inch). Still, the AFRs flowed so much more cfm at all lift values (see the charts) than the old castings that we couldn't wait to see the difference on the dyno.

Dyno Time
In Part 1, the five upgrades upped the ante to 402 rear wheel horsepower at 5,400 rpm and 415 lb-ft of torque at 4,800 rpm (this month's baseline). Once again at SLP Performance Parts we met up with Ken Estell (engineering fabricator) and Will Seppelt (product design engineer) and strapped down the Shoebox. Hank Daneicki (director of engineering) handled the dyno-driving duties.

Hank put the hammer down and we witnessed 452 rear wheel horsepower when he let off the gas at 6,200 rpm (this was the shift light setting). On all the previous pulls Hank was letting up at 6,200 since the previous peak power was at 5,400 rpm. Now at 5,400 rpm, the AFRs helped produce 35 more horsepower, and at 6,200 rpm the power was up by 79 hp! With more pulls to come, we didn't want to risk revving the old Rat too high.

During initial back-to-back pulls we noticed the air/fuel mixture ratio was too lean at 13.5. We reached into our Holley jet box for size #82 jets to replace the Holley 950 HP's stock #79 jets on all four corners. The bigger jets added response and three rear wheel horsepower. Still, the A/F was too lean at 13.3 to 13.4. Next, we swapped the high-speed air bleeds (#32s) for a richer set (28s). This brought the A/F to a safe but slightly rich 12.6 along with consistent power output. If we'd tested on a cool day at 65 degrees Fahrenheit, the A/F would have been close to an ideal 12.9. It was not conducive for us to further try more tuning on this extra hot and humid day. Besides, after realizing 82 rear wheel horsepower at 6,200 rpm from a head swap, we were content to leave well enough alone.

Everyone's heard the saying, "It's all in the combination." Selecting the right parts is usually a phone call to the company's tech line. Be thorough with the specifications of the motor, driveline, vehicle weight, and intended purpose. This big-block responded favorably to its new upgrades, and Joey D enjoys driving his No-Jive-Five-Five more than ever. The head swap certainly helped the whole combination come together to become a serious street/strip contender.


Air Flow Research
Valencia, CA 91355



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