Light rockers are a must because they reduce mass in the valvetrain. Reducing the “moment of inertia” with lighter rocker arms allows the engine to rev higher with the same springs.
Today, engine builders and racers have a wide variety of performance rocker arms and rocker systems from which to choose. There are the “economy” aluminum rockers typically made from diecast aluminum that provide an upgrade in performance over stock stamped steel rockers. But for more demanding applications, upgrading to CNC extruded or forged aluminum rockers or steel rockers is often necessary.
Rocker arms obviously have to be strong to handle the loads that are placed upon them, but reducing the mass on the valve side of the rocker arm has more of a positive effect on reducing inertia than changing the mass on the pushrod side of the rocker arm. This also explains why larger or stiffer pushrods that weigh more than stock pushrods have minimal effect on valvetrain momentum. You want stiffer and stronger pushrods for reliability and valvetrain stability, especially with higher valve spring pressures in a highly modified high revving engine.
Some of today’s steel rockers are just as light if not slightly lighter than a comparable performance aluminum rocker. Steel can safely handle a lot of valve spring pressure, up to 950 pounds or higher say the people who make such rockers. Steel has better fatigue strength and stiffness than aluminum, and will stand up to the rigors of racing for a longer period of time – often 2X to 4X as long as comparable aluminum rockers.
By comparison, the typical economy diecast aluminum rockers should not be used with more than 350 to 450 pounds of open spring pressure depending on the brand of rocker. Extruded aluminum rockers can usually handle up to 700 pounds of open spring pressure, with some rated for as much as 900 pound springs. Always go by what the rocker arm manufacturer says their arms can safely handle. Don’t push the rockers beyond their rated capacity unless you want to break something.
Something else to pay close attention to when choosing rockers is the design of the rollers and needle bearings. More needle bearings in the center bearing is better because it spreads the load over a larger surface for improved durability. The rollers on the tips of many rocker arms do not have needle bearings, but some do – which helps reduce friction and valve stem wear.
The type of rocker arms that are permitted may be restricted by the rules in some racing applications. If the rules call for “stock appearing” rocker arms or stamped steel rockers, that doesn’t mean you’re stuck using the stock rockers. Many aftermarket companies offer stock appearing stamped steel rockers that are made of stronger alloys for improved reliability.
And even if rules are not a limiting factor, stamped steel rockers can usually handle engine speeds up to 6,500 rpm and valve lifts of up to .600˝ as long as the rocker slot has sufficient stud clearance to handle a high lift cam. The same goes for cast steel rockers on Ford and Chrysler engines that use some type of shaft mounted rocker setup.
For engine applications that demand a step up, replacing the stock stamped or cast steel rockers with aluminum roller rockers will typically produce a gain of 10 to 15 hp with the same lift ratio, and even more of a power gain with a higher lift ratio. The extra power comes from the reduction in friction provided by the roller rockers – which also helps keep the oil cooler, too.