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

Dan Foley Apr 1, 2008 0 Comment(s)
Sucp_0804_16_z 1955_chevy_modern_hotrod Superflow_flow_bench 2/19

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.




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