Chevy 496 Comp Cams Roller Rockers & Valvespring Upgrade - The Sweet Spot

Curing Valve Float With Lifters And Springs

Sean Haggai Feb 1, 2010 0 Comment(s)

Dyno Test 1
Brulé began to install each new rocker arm into place. Since this is still a hydraulic valvetrain setup we would not need to adjust the lash. With everything buttoned up, it was time to make a pull and see the results. In this instance, we found a slight gain in horsepower and torque. We also managed to clean up the stumble in the upper rpm.

BASELINE PRO MAGNUM ROCKERS GAIN
TIMING 42 degrees TIMING 42 degrees ~
JETS 80/80 JETS 80/80 ~
AVG HP 488 AVG HP 490 +2
AVG TQ 540 AVG TQ 541 +1
PEAK HP 566 @ 5,700 PEAK HP 568 @ 5,900 +2
PEAK TQ 577 @ 3,700 PEAK TQ 578 @ 3,700 +1

Dyno Test 2
Brulé began the teardown by unbolting the intake and removing it. He then removed each lifter and replaced them with the "R" series lifters. The new lifters are a simple drop-in item and didn't alter the pushrod length whatsoever. We then installed the Ultra-Pro.

1002chp_07_z Chevy_496_comp_cams_roller_rockers_valvespring_upgrade Performance_parts 3/15

PRO MAGNUM LIFTERS + steel rockers GAIN
TIMING 42 degrees ~
JETS 80/80 ~
AVG HP 495 +7
AVG TQ 543 +3
PEAK HP 576 @ 5,900 +10
PEAK TQ 580 @ 3,700 +3

Dyno Test 3
After reviewing the results, the 496ci gained torque and horsepower. Brulé still wasn't completely satisfied though, noting "The cam should have still been able to make power up to the suggested 6,100 rpm." With that he suggested that the valvesprings may be too weak. The combination of a higher tolerance lifter and higher revving cam may be overwhelming the spring. It was then Brulé decided a spring swap and a set of titanium retainers (PN 721-16) would allow more control over the valve at high rpm. Titanium is lighter and stronger than steel, which allows for additional engine speed. Sure enough, power was up again and even helped to smooth out the entire power curve.

1002chp_11_z Chevy_496_comp_cams_roller_rockers_valvespring_upgrade Performance_torque_gains 6/15

DUAL SPRINGS + PRO MAGNUM LIFTERS + STEEL ROCKERS GAIN
TIMING 42 degrees ~
JETS 80/80 ~
AVG HP 499 +11
AVG TQ 547 +7
PEAK HP 579 @ 6,000 +13
PEAK TQ 583 @ 3,700 +6

While our build isn't a high-budget racer, the 496ci is still seeing gains with high rpm punishment. Since the camshaft is still rated to make power up to 6,100 rpm, we needed a stiffer valvespring to handle the upper rpm. The good news is, these springs are a direct swap and do not require any additional machining to the RHS cylinder heads.

1002chp_10_z Chevy_496_comp_cams_roller_rockers_valvespring_upgrade Performance_valve_springs 7/15

VALVESPRINGS
SPRINGS Dual
OUTSIDE DIAMETER 1.535-inch
SEAT LOAD 148 lbs @ 1.900-inch
OPEN 456 lbs @ 1.250-inch
SPRING RATE 473 lb/in

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