The Importance Of The Rocker Arm
One of the most important components in your engine is the rocker arm; it is also one of the most vulnerable. As the turning point of the valve train, the rocker arm is basically a sophisticated lever that channels radial movement from the cam lobe into linear movement at the valve. This is a highly critical process. Due to stresses and vibrations, which are more prevalent during high speed operation, rocker arms undergo what is known as "deflection." Severe rocker arm deflection causes inefficient engine performance, and often results in metal fatigue leading to increased wear and friction in the valve train and eventually engine failure.
There are three basic ways to increase power through a rocker arm change.
1. Lift the valve more.
By increasing the rocker arm ratio, it's possible to increase valve lift without ever touching the camshaft. Valve lift can typically be increased as much as 10 percent by increasing rocker ratio.
2. Make the rocker arm stiffer.
To increase stiffness, look at three options: material, geometry and the rocker's holding fixture. The easiest way is to switch to chromemoly steel. Although heavier than some other materials, it can offer some design advantages and have much thinner sections than aluminum due to its superior strength density. Stiffness of the mounting is just as important as the stiffness of the rocker body. For the ultimate in high performance, shaft-mounted rockers may be the way to go.
3. Decrease the moment of inertia.
The moment of inertia is the rocker's resistance to rotation. The higher this measurement, the more valve spring pressure it takes to control the rocker arm instead of the valves - losing rpm and horsepower. The moment of inertia is lowered by lightening the rocker arm's weight, particularly at areas that are farther from the trunion. Two ways you can do this are by switching to a lighter weight material or by removing mass from the rocker body design.
Until recently, aluminum rocker arms have been considered a more affordable but less durable option to steel rockers. Because when directly compared to steel, aluminum requires more material to handle the stress of a given force. Since more material is required and there is a limited amount of space available in the trunion, the bearing and axle are typically smaller in an aluminum rocker arm. Previous designs weren't able to be used in extreme applications and featured decreased stiffness and increased deflection. But COMP Cams® has developed aluminum rockers that use precision-sorted needle bearing trunions to withstand both elevated spring pressures of 350 lbs) and valve lift. The newest COMP® aluminum rockers - the Ultra-Golds® - actually have the highest rocker-to-valve spring clearance of any aluminum rocker - up to 1.650" valve spring O.D. And while these newest aluminum rockers are lightweight, they are still incredibly strong and feature a lifetime warranty.
COMP Cams® steel rocker arms are all constructed from 8620 or 8650 chromemoly steel, which is a higher grade material that makes them extremely durable and tough. The material keeps them from flexing, and they have large trunions and more needle bearings, which allow the load to be more evenly spread and the rocker to last longer. Steel can thus be run in harsh environments without fatigue issues. Steel will actually only become weaker to a certain point and then stop and retain nearly half of its original strength throughout its life. And some COMP® steel rockers are even lighter than some aluminum because COMP® has reduced mass in low stress areas.
Stud vs. Shaft-Mounted Rocker Arms
Rocker design continues to evolve as more aggressive cam profiles and cylinder heads are developed. Stud mounted rockers have evolved over the years. Starting as a simple ball-and-socket mounted stamped steel piece, the first modifi cation was to change the mount to a roller bearing and a transverse mounting axle. Next, larger screw-in studs were added. Soon, geometric designs had to change and stiffer material needed to be used, giving way to the innovative arched web design as seen in today's Ultra Pro Magnum™ Rockers from COMP Cams®.
The next step in rocker arm technology is the shaft mounted rocker. Rather than being mounted on a stud, a horizontal shaft works as the fulcrum. This significantly increases the mounting stiffness and valve train stability. However, shaft-mounted systems are designed for highend performance applications and can make a big impact on your wallet (sometimes as much as $3000). A cost-effective alternative is to use a stud girdle to reduce deflection with stud mounted rockers.