Rocker Arms 101

Everything You Always Wanted To Know About SBC Valvetrain Tech But Were Afraid To Ask

Brian Reese Aug 23, 2007 0 Comment(s)
Vemp_0703_07_z Corvette_rocker_arms Narrow_body_comparison 1/31

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.

This same friction-fighting design savvy evolved beyond the mounting joint and ultimately was applied to the rocker-arm tip. The slider-tip design is quite simple and fairly durable, but far from friction friendly and not especially suited for high lift and high RPM. The factory slider-type rocker-arm tip (standard on all GEN I-IV SBC engines with the exception of the LT4) simply rocks-and slides-across the top of the valve stem as it's actuated. The slider tip is not only a friction source, it's also known to push on the valve stem during the actuation process, potentially unsettling the valvetrain. By replacing the slider tip with a roller tip, friction is reduced, and the valve is again stabilized. The roller tip may also help facilitate higher lift, faster actuation, and high-rpm usage.

Reductions in valvetrain friction offer a nice side effect as well. As friction drops, so does the demand for oil. With the demand for oil reduced, the delivery of oil to the valvetrain can be safely restricted. This also means less windage of oil as it returns to the sump. When properly engineered, oil-restriction techniques can unlock a few extra ponies.

Vemp_0703_08_z Corvette_rocker_arms Hi_tech_roller_rockers 2/31

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.

Beyond high ratios and friction-abatement technologies, performance-rocker-swap talk must include discussions of materials, strength, and stability. The most common rocker material is steel. Stamped steel was the OEM standard for Gen I and II, while cast steel was-and is-the standard for Gen III and IV. While these are suitable for OEM and basic performance, the aftermarket and racing communities demand more exotic options. Nothing screams high performance more than a set of anodized-aluminum roller rockers, regardless of their true positive effect. Nonetheless, high-strength alloy aluminum rocker arms are good, lightweight performers. Basic aluminum rocker arms are available with cast-alloy or extruded bodies, and high-end aluminum rocker arms are available machined from billet alloys.

Chrome-moly steel is a common material for high-performance parts, and rocker arms are no exception. The strength and rigidity of this mater-ial is hard to beat. Chrome-moly is used for some performance rocker bodies, but it's the material of choice for performance rocker-arm trunnions and roller axles. Other high-strength alloy steels are used in high-end, precision rocker arms, with rock-like rigidity for high-rpm race applications. For the ultimate in valvetrain performance and stability, shaft-mount rocker-arm systems are the way to go.

Vemp_0703_09_z Corvette_rocker_arms Comp_pro_magnum 3/31

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.

Expounding on the material engineering of rocker arms, Scooter Brothers, cofounder of Comp Cams, explains some interesting facts about steel-bodied rocker arms. Scooter states that chrome-moly steel, although heavier than other materials, can offer some design advantages and have much thinner sections than aluminum due to its superior strength density. Generally speaking, it takes at least two times the aluminum to approach the strength of steel. The moment of inertia, or performance mass, of properly engineered steel parts can actually be close to that of aluminum. In other words, before jumping for lightweight aluminum rockers, it's important to realize that the effective weight of a quality steel unit may be comparable.

Now that you've passed "Rocker Arms 101," it's time to pick the right set of rocker arms for your engine. Selecting the right rockers can be a daunting task, but following a few basic guidelines can help. First, not all rockers fit all engines. Narrow the search to those rockers applicable for your specific application. For instance, Gen I rockers won't fit a Gen III engine, and so forth. Some high-end aftermarket rockers only work on certain head types, like shaft rockers for SBC Gen I. Confirm compatibility before moving forward.

Next, ask yourself if you have the guts for modifications. In other words, are you ready to clearance valve covers or heads or convert to screw-in studs to make the rockers fit? Narrow your search for parts within your modification tolerance, and find out what else is needed. Some rocker swaps require adding a set of pushrods, locking nuts, guideplates, or other accoutrements. Get a complete understanding of what is needed before making a selection.

While most factory springs can handle a small increase in valve lift from the addition of higher-ratio rocker arms, it's usually recommended to swap in a set of matching performance valvesprings to go with the new rockers. Springs are often overlooked, which can prove costly if a stock spring breaks. Don't go cheap on springs; it's good insurance and usually quite affordable.

And, in the end, the all-important budget will probably help with your decision.

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