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Rocker Arms 101
Everything You Always Wanted To Know About SBC Valvetrain Tech But Were Afraid To Ask
Aug 23, 2007
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Rocker Arms 101
The most basic rocker-arm design is the stamped-steel type. The design originated early in the overhead-valve era and was standard issue on production small-block Chevy engines from '55 through '96. Only a few insignificant design changes occurred during the life of the stamped rocker. Most notably, a self-aligning version replaced pushrod-guideplate-type rockers across the board in '87. The stamped rocker is basic, inexpensive, durable, and gets the job done. The Comp Cams Hi-Energy stamped-steel rocker arms shown here offer a high-quality replacement for budget or stocker-minded builds.
Comp also offers a basic cast rocker arm with a roller tip. Called the Magnum Roller, this rocker arm uses a ball-type stud mount. The body is cast from alloy steel and heat-treated for strength, rigidity, and longevity. This rocker arm is available in high-ratio versions as well.
The Pro Magnum roller rocker from Comp offers a roller trunnion in combination with a roller tip. The Pro Magnum line is offered in both stock and higher ratios. These "full-roller" rockers minimize friction and are an excellent option for street and race applications alike.
The red-anodized-aluminum roller rocker arm from Comp offers both looks and performance. These rockers are available in a range of ratios and can be used with either 3/8-inch or 7/16-inch studs.
Late-model ('87-'96) Vettes require Comp's special narrow-body, self-aligning rockers. The narrow body allows them to fit under center-bolt valve covers, and the self-aligning tips satisfy '87-and-up valvetrains.
The narrow-body rocker on the left is clearly distinguished from the traditional rocker on the right. The wide-body rockers are for perimeter-bolt valve covers and guideplate valvetrains only.
Comp Cams also offers a hot-rod-version full-roller rocker arm. These Hi-Tech stainless rocker arms are precision-cast from stainless steel. They offer a wide range of exacting ratios for various applications and feature pushrod socket inserts for maximum strength and durability. Thanks to their exotic material, they are the strongest, most rigid rocker Comp offers for the SBC.
Gen III and IV engines have a unique and exclusive rocker design. All '97-'07 Gen III and IV engines share the same 1.7:1 rocker arm save for the LS7, which gets an application-specific design. (Offset around the big ports, longer in length, and with a 1.8 ratio, the LS7 unit is incompatible with all other Gen III/IV engines.) Comp offers both stock and high-ratio (1.85) rockers based on the Pro Magnum design. The factory rocker arms on these engines are net-built with no rocker-arm adjustment possible. Comp's Pro Magnums introduce a traditional adjustable setup and incorporate a retro-fit guideplate-alignment system. Interestingly, the small end of the studs shown here screw into the cylinder head.
From simple to advanced, the rocker designs are compared from left to right. The center Pro Magnum roller features a self-aligning roller tip and roller-bearing trunnion. The Hi-Tech stainless rocker on the right features a high-strength pushrod insert to stand up to punishment at high lift and speeds.
This photo shows a comparison of a self-aligning tip (left) and a guideplate-type tip (right). The two are not interchangeable.
The self-aligning tip design on the left uses walls that extend past the roller on each side to align the rocker arm over the valve tip. In contrast, the rocker on the right has a traditional tip and must rely on a pushrod guideplate to center itself with the valve tip.
The predecessor to self-aligning rocker arms is the pushrod guideplate. These hardened plates have slots for guiding pushrods in line. Comp offers high-strength performance plates, considered a must for any performance guideplate-type head.
The four basic rocker arms for the Gen I and II SBC are shown. From left to right are the stock rocker and trunnion ball, the Comp Magnum roller and trunnion ball, the Pro Magnum roller, and finally the aluminum roller.
Shaft-mount rockers are used in some high-end builds. Their use on Gen I SBC engines is typically limited to use with an aftermarket cylinder head. However, factory Gen III and IV heads readily accept shaft assemblies. The shown shaft-mount adjustable aluminum roller kit (1.8:1 ratio) is offered for Gen III and IV engines and introduces an adjustment socket as well.
The Gen III/IV rocker arm is nothing like traditional SBC rocker arms. The stock rocker shown in the foreground is made from cast steel and features a very basic roller trunnion. The factory ratio is a whopping 1.7:1, but aftermarket ratios of 1.85:1 are common.
The traditional SBC rocker-stud size is 3/8 inch (middle). A lot of racers convert SBC studs to the stronger big-block Chevy (BBC) size of 7/16 inch (bottom). Both of these sizes dwarf the Gen III and IV M8 stud (top).
The vast majority of SBC iron heads came with press-in studs. Converting to screw-in studs is a common modification and suits performance builds. Comp Cams offers a special cutting tool for facing off the head after the factory stud has been removed. The smooth machined surface left after cutting is critical to completing the conversion properly.
Factory rockers are held in place with a special deformation locknut. Comp offers slick adjustable locknuts, which utilize a superior set-screw locking insert. These nuts are unique to the rocker type employed and should not be intermixed.
Comp's narrow-body, self-aligning, aluminum rockers can boost the effective valve lift of a '95-'96 LT1 from 0.447/0.459 to approximately 0.477/0.490-more than the vaunted '96 LT4. Additional benefits include reduced valvetrain friction and oil temperatures.
Our calculations indicated the 1.6 rockers would place our LT1's valve lift uncomfortably close to the rated limit of the factory springs (0.500 inches). To be safe, we upgraded to beehive-style springs, steel locks, and retainers, also from Comp.
Anti-Venom's Greg Lovell begins the installation by using compressed air to remove dirt and debris from the area around the intake manifold and valve covers.
With the valve cover removed, we can get a good look at the factory valvetrain gear. Not terribly attractive, is it?
Next, Lovell removes the old rocker arms and valvesprings.
This photo clearly shows the dimensional differences between the stock LT1 valvespring (left) and the beefier Comp beehive unit.
When swapping valvesprings, you need a valvespring-compressor tool. Do yourself a favor and get a good one. This cheapo job, which we picked up from a local auto-parts store, fell slowly but irretrievably apart as the day wore on, driving the normally mild-mannered Lovell to the brink of a towering psychosis.
With the new springs finally in place, Lovell drops in the Comp rockers and secures them to the head.
Here's our freshly upgraded LT1 valvetrain. Stylish, no?
Prior to startup, Lovell gives everything a good hosing down with Comp's new Valve Train Assembly Spray (PN 106). Because it's dispensed in aerosol form, the spray is considerably easier to work with than traditional tube-based lubes. Better yet, it's compatible with all synthetic and mineral-based oils.
In the end, the rocker/spring swap netted us as much as 15 additional horsepower and 17 more lb-ft of torque at the rear wheels. That's significantly more than we'd expect to see from a rocker upgrade alone, indicating the stiffer springs were really doing their job. Thanks to a few carefully selected upgrades, our auto-trans '96 is now making approximately the same horsepower as-and considerably more torque than-an early C5. And we're just getting started.
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