The rocker arms play a more important role than ever these days in high performance valvetrains. The rockers are the teeter-totters that translate the upward motion of the lifters and pushrods to the downward motion that opens the valves. It seems like a relatively simple task, but it demands the utmost from the design of the rockers and the materials from which they are made.
Aluminum roller rockers with roller needle bearing fulcrums and roller tips have been around for decades. The main advantage with the roller rockers is that they reduce friction compared to a standard stamped steel or cast iron rocker arm.
The basic technology has not changed that much over the years. What has changed are the lift ratios that some of today’s rockers are capable of delivering, the high valve spring loads rocker arms in some high revving engines have to handle, and the strength and durability requirements that end users have come to expect from a set of high end performance rocker arms.
One of the qualities every engine builder wants in a set of performance rocker arms is stability. The more stable the rockers, the more stable the valvetrain and the better the engine performs at high rpm. Shaft-mounted rockers typically offer better stability than stud-mounted rockers. Studs can flex and wobble at high rpms, causing deflection or even misalignment between the pushrods, rockers and valves.
Pushrod deflection can be minimized by using thicker wall, larger diameter stiffer pushrods. Valve harmonics and float can be addressed by running heavier, stiffer springs, double or triple springs or conical springs. But rocker arm deflection can only be addressed by beefing up or modifying the rocker arms and mounting system.
For all-out racing applications, this often means replacing the stock rocker arms with roller rockers and installing a stud girdle to reduce stud movement, or converting stud-mounted rockers to a shaft-mounted rocker system.
The Advantages of Shaft- Mounted Rocker Arms
Shaft-mounted rocker systems are available for a wide variety of engine applications. They are the “in” setup these days for many forms of professional racing. The cost of a good shaft-mounted rocker system can range from $600 to $1,800 or more depending on the supplier, what you need and where you buy it. Advantages for shaft-mounted rockers include:
• Increased rigidity and reliability. Supporting the rockers on a rigid steel or aluminum shaft means the rockers can’t deviate from their fixed location due to stud flex or vertical motion on the rocker stud. The stiffness provided by the shaft holds all the rockers in perfect alignment and allows them to safely handle higher loads and rpms.
For extra durability, some suppliers offer steel rocker arms with their shaft-mounted systems. Steel provides extra strength and durability with minimal weight penalty to eliminate concerns over rocker arm breakage. Shaft-mounted rockers also don’t require a slot cutout on the underside of the rocker body to clear a stud, so shaft rockers are inherently stronger.
• More horsepower. Reduced valvetrain friction combined with improved valvetrain control means the engine can handle higher camshaft lift ratios and seat pressures while still maintaining accurate valve timing and control.
For engines that are running high valve spring pressures (say 800 to 1,000 lbs. of open spring pressure or more), a shaft-mounted rocker system can provide the extra degree of insurance to reduce the risk of something breaking.
• Easier installation. Most suppliers of shaft-mounted rockers work closely with aftermarket cylinder head companies to create bolt-on systems that are designed for specific cylinder heads. This eliminates or minimizes the amount of machine work that’s required to adapt a shaft-mounted rocker arm system to a particular head.
Most suppliers can custom make a shaft-mounted rocker system for almost any motor with any offset or lift ratio you require.
• Easier valve lash adjustments. Shaft-mounted rockers typically hold valve lash adjustments longer and are easier to adjust than stud-mounted rockers with a girdle overhead. The adjusters on the rockers or the shaft are easy to get at and adjust. For a weekend racer, this can be a real time-saver between rounds.
Higher Lift Ratios
The lift ratio of the rocker arms multiplies the amount of valve lift generated by the cam lobes. The maximum amount of lift that can be achieved with a given camshaft is often limited by the size of the lobes that will fit through the engine’s cam bores.
A cam grinder can achieve more valve lift by reducing the diameter of the base circle on the cam. But there’s a limit as to how much the base circle can be reduced before it creates lifter problems.
Increasing the lift ratio of the rocker arms is the easiest way to get more effective valve lift out of a given cam lobe profile. Increasing total valve lift and the velocity at which the valves open and close increases volumetric efficiency for more power, and typically boosts top end horsepower without sacrificing too much low rpm torque.
Aftermarket rocker arms are available in a wide range of lift ratios, some as high as 2.25 to 1 or more! But the higher the lift ratio of the rocker arms, the more additional modifications you may have to make to prevent coil bind in the valve springs or interference problems between the tops of the valve guides and the valve spring retainers.
Durability can also be a concern when running extremely high valve spring pressures and lift ratios. Lightweight rocker arms are obviously a plus for high rpm applications, but strength is also essential to prevent breakage. So for high lift, high rpm, high valve spring pressure applications, steel roller tip rockers have become popular for serious racers.
Steel has better fatigue strength and stiffness than aluminum and it can absorb more abuse than aluminum over time. Aluminum rockers that used to last a season of hard racing before they need to be rebuilt or replaced can be swapped for steel rockers that can often last several racing seasons.
Friction reduction is also essential with high performance rocker arms. The needle bearing fulcrums and roller tips do a good job of providing the required friction reduction but do require a steady supply of lubrication.
Roller tip rockers are a must with high lift ratios because of the increased arc of travel the tip of the rocker follows as it opens and closes the valve. The roller tip reduces the sideways thrust and scrubbing on the tip of the valve stem.
Inexpensive die cast aluminum rockers are a good upgrade for street performance use or racing applications where high pressure springs are not required. Extruded aluminum rockers are a step up from die cast aluminum rockers and provide increased strength and durability for more demanding applications.
Extruded rockers are made from 6061 T6 billet aluminum so there is no porosity in the metal as can be the case with die cast rockers. Extruded rockers are usually CNC machined and often hand finished to specifications. Extruded aluminum rockers are typically recommended for higher lift ratios.
As mentioned earlier, steel rockers may be the best choice for severe duty applications that require extra strength and durability (engines with very stiff valve springs, high lift ratios and/or heavy valvetrain components).
The steel is usually a high grade stainless alloy with a micropolished finish and can handle spring pressures up to 950 pounds or higher (versus maybe 750 to 800 pounds for many extruded aluminum rockers, though some aluminum rockers can handle up to 1,000 pounds in a BB Chevy engine).
However, expect to pay more for a set of steel rockers because they are more expensive to manufacture and more difficult to machine.
Some rocker arm suppliers say most racers probably don’t really need steel rockers as long as they are using a high quality aluminum rocker arm system. They can save the money that a set of steel rockers would cost and put it toward other engine upgrades.
Others disagree and say the extra reliability and durability provided by steel rockers is well worth the extra cost, and that steel rockers will pay for themselves by outlasting aluminum rockers.
Comp Cams will be adding LS1, LS2, LS3 and LS6 rocker applications to its Ultra-Gold Arc Series of rocker arms in early 2013. Like the other rockers in this series, they are made in the USA and were designed using modern CAD and FEA software to improve the strength while minimizing weight.
Comp Cams says these new rockers are much stronger than any of the competing extruded aluminum rockers and can be installed on a stock unmodified head. They come with their own steel pedestals and have upgraded trunions and bearings compared to the stock rockers. Available lift ratios are 1.7 and 1.8 with either bolt down or bolt down adjustable configurations.
Also new from Comp Cams are stronger half inch diameter studs for screw-in stud mounted rockers. The thicker studs reduce stud flex to reduce the risk of stud breakage in high revving engines.
Crane Cams recently unveiled its new Chevy LS V8 family of rocker arms for endurance racing applications. Testing is still in progress but the new rocker arms should be available in early 2013. These will be bolt-on rockers that require no modifications. Crane has also been upgrading its entire product line of performance rockers with stronger high temperature materials, and tightening its manufacturing tolerances with new CNC machining equipment.
Crower has a variety of new billet rockers that include oil ports for lubricating the valve springs. Getting oil to the springs quickly following a cold start is critical for maintaining spring longevity. Crower also has more new steel rockers applications including custom shaft rockers for BB Chevy.
Elgin Industries has recently rolled out its “Rolling Thunder” Pro-Stock Stainless Steel Rockers. These rockers feature all stainless-steel construction with extra large, full needle trunions and larger roller tips to help eliminate wear.
Applications include 1.5 and 1.6 rocker ratios for SB Chevy (with long slots), 1.72 rockers for BB Chevy, and 1.6 rockers for 3/8? and 7/16? stud diameter Ford applications.
Rick Simko of Elgin says that all-stainless rocker arms like these eliminate deflection at maximum RPMs and construction designs offer increased power and durability.
“The extra-large, full-needle trunions provide increased horsepower and faster response, and the large roller tip design helps eliminate wear,” says Simko.
Harland Sharp’s “D-Force” line of 2024 billet aluminum roller rockers provides an upgrade for 12V and 24V Cummins diesel engines, 6.0L and 7.3L Ford Powerstroke diesel engines, 6.5L and 6.6L General Motors Duramax diesel engines and International Harvester and Yanmar 3 cylinder diesel engines. The diesel rockers are designed for off-road applications and sled pulling but are NOT recommended for daily street use. Increased lift ratios are available.
Howards Cams has a line of billet aluminum rockers that can handle up to 800 psi open valve spring pressure and up to .800 inch of valve lift for SB/BB Chevy and LS engines. The rockers also come with a unique limited lifetime warranty, something which nobody else offers, according to company spokespeople.
Randy Becker Jr. of Harland Sharp said his company is currently developing some new bolt-on pedestal rockers for GM 3.1, 3.4 and 4.3L V6 engines. The new rockers should be available sometime in 2013.
Jesel continues to add new rockers for recently released cylinder heads including some new steel rockers applications. Bob McDonald of Jesel says engine builders today want steel rockers for more and more applications, and especially for the exhaust valves where high cylinder pressures create greater resistance to the valve opening. Heat can also be an issue on the exhaust side. Higher lift ratios and stiffer springs are also requiring a change to steel rockers.
Manton makes a variety of steel rockers for Chrysler Hemi Top Alcohol and Pro Fuel engine applications. The latest offering is a new Roller Tip I-Beam rocker arm for exhaust valves. The rocker can handle engine speeds in excess of 10,500 rpm and withstand the high loading created by extreme exhaust pressures in these engines. The rockers are made from billet 4340 steel and heat treated to 305,000 psi. The rockers also feature oversized roller bearings and pins, and oiling is provided to the rocker adjuster screw.
PRW introduced its LS Series of pedestal/shaft mount aluminum rocker arm systems in 2011 as an upgrade over the stock GM rockers. The number of LS applications since then has grown as have the rocker applications available from PRW. These rockers are not a simple “drop-in” replacement for the stock LS parts, but the PRW rocker systems do include all the specialty tools and parts that are needed for an easy installation. The rockers do require extra clearance under the rocker arms, which can be easily solved with valve cover risers from PRW or by replacing the stock valve covers with PRW’s valve covers.
The LS Series rockers are made of 6061 T6 billet aluminum with full complement needle bearings and nose roller. The rockers are fully adjustable for use with solid or hydraulic lifters and up to 750 pounds of open valve spring pressure. The CNC machined steel pedestal replaces the OEM die cast aluminum design. All mounting bolts and adjusters are SCM-4135 custom alloy with rolled threads. Pushrod length checkers are included to determine the exact pushrod length required.
Scorpion has been a long time supplier of stud mounted aluminum rockers, but will now be offering their first shaft mounted aluminum rocker arm system for 23 degree SB Chevy heads. Next will come shaft rockers for 18 degree SB Chevy heads, followed by shaft rockers for BB Chevy, SB Ford and Chevy LS applications. The new shaft mounted rockers will be called “Endurance Series” and will be competitively priced with other shaft rocker systems.
T&D Machine is currently working on developing some new LS rockers to add to their existing line of aluminum and steel LS rockers, which include LS1, LS2, LS3, LS6, LS7 and L92 engines. Standard rocker ratios include 1.7 and 1.8 with other lift ratios available on request. “If an engine has pushrods, we make rockers to fit it,” said Phil Elliott. “We currently are not doing any overhead cam applications except for the OHC followers on 4.6L V8 Fords (2, 3 and 4-valve versions) and the older 427 OHC engines.”