Keeping a valvetrain happy under stressful operating conditions should be a priority when you want to make big power with an engine, and the rocker arms are one area where you can make this happen for any engine combination. To help your rockers keep on rocking, going to a shaft-mount design is a great option for any engine, including the LSX family of powerplants.
Typically, rocker arms have only a single mounting point on the cylinder head. Going to a shaft-mounted system will improve the stiffness of the entire rocker system since they are all tied together on one shaft. Getting the rocker arm off of a single bolt and riding on a shaft adds a high degree of rigidity and helps the rocker arm do its job more efficiently with more strength.
Chris Potter from COMP Cams explains how a shaft rocker system helps an engine.
“By using a shaft and now multiple fasteners to constrain the rocker arms, each individual rocker is prevented from being able to twist about the bolt axis. This means that the rocker tip geometry maintains better contact with the valve tip, preventing abnormal wear on both components and ensuring that the rocker tip follows the valve tip as designed. This is especially beneficial on the LS3 and LS7 engines, where the intake rocker is offset. This offset design awkwardly loads the rocker arm and adversely affects the contact with the valve tip, causing accelerated wear.”
Besides adding strength, a shaft-mounted rocker system can increase an engine’s ability to perform. There’s a reason you see many high-horsepower engines using a shaft-mounted rocker setup rather than the traditional single bolt system.
“A stiffer rocker arm system decreases the deflection between the camshaft and the valve. More camshaft lift is transferred to valve lift. This means that any given camshaft will act slightly larger, as less of its performance is lost due to parts moving in ways that aren’t desired. The second is that a stiffer rocker system maintains geometry between the rocker pad and the valve tip. By maintaining proper geometry, the rocker can see more lift than it could with the stock trunnion and bolt. Think about it as being able to consistently run .680-inch lift instead of .660-inch lift for long periods without tearing up the rocker pad or valve tip,” Potter says.
LS-based engines use a single bolt to hold the rocker arm to the cylinder head; the system works, however, as you add horsepower it becomes a failure point. Seeing an opportunity for improvement, COMP created the Max-Lift BSR Shaft Rocker System for LSX applications. The cool thing about the BSR system is that it allows you to use a stock GM rocker arm.
“The stock rocker is a very good rocker design at an exceptional price-point. It’s hard to beat its performance. However, it does have shortcomings as a whole system. We’ve sold trunnion upgrades for years to eliminate some of the failure modes of the stock trunnions. The shaft system just improves the system even further with bushings and tying everything together. As mentioned earlier, the extra rigidity also helps us achieve more lift out of the stock rocker without any detriment to the longevity of the rocker or valve tip,” Potter explains.
By increasing the stiffness, the BSR system allows for more camshaft to valve lift. This stiffness also keeps the geometry of the rocker in the correct location for the valve tip. All of this leads to the ability to add even more lift to a camshaft without causing durability issues, and a decreased likelihood of the valvetrain going out of control as the cam lobe becomes more aggressive.
“Our shaft system uses a tri-layer bushing that will reduce friction over a standard bronze bushing, increase bearing area over a needle bearing, and decrease deflection associated with a needle bearing. All three of these create durability improvements in the rocker arm system that will increase longevity and reduce wear over the life of the engine. And that’s just due to the bushing selection,” Potter says.
Going to a shaft rocker system is one way you can help bomb-proof your LSX-based engine’s valvetrain. The additional rigidity the shaft rocker system provides will help keep everything moving how it should and allow you to make plenty of horsepower along the way.