By Larry Carley
|As rockers continue to evolve, the ongoing trends toward lighter weight and stronger designs will continue. Many rocker arm manufacturers also offer custom rockers, as well as a wide range of ratios and rocker styles (stud mount, pedestal and shaft mount).|
Horsepower is in the heads. But for a cylinder head to breathe efficiently, the valvetrain must be rigid and strong to minimize flex, but also lightweight. For most performance applications, that means replacing the stock rocker arms, valve springs and pushrods with some type of aftermarket roller rocker arms, stiffer valve springs and stronger pushrods.
The way in which rocker arms are designed has changed in recent years. Many companies now use sophisticated computer software to develop new rocker arm designs. An engineer sits down in front of a computer and uses a computer-aided design (CAD) program to define the basic dimensions, size, shape, length and rocker arm ratio of the rocker arm. Then he uses a finite element analysis (FEA) software program to simulate loads on the rocker arm to see how well it holds up. The FEA program reveals where the greatest stresses are so the rocker arm can be strengthened in critical areas if necessary. The simulation software also reveals the areas of the rocker that are not under stress so additional metal can be removed to lighten the rocker. By pretesting a new rocker arm design before an actual prototype is ever built, the engineer can optimize the rocker for the best combination of weight and strength.
Once the engineer is satisfied with the design and simulated test results, the next step is to make up some prototype rockers for real world testing. The rockers are then installed on an engine and subjected to durability and dyno testing. If everything goes well, the next step would be to install the new rockers on some actual racing engines and see how well they perform and hold up. And if that goes well, the last step is to mass produce, package and market the finished product to engine builders.
|A polished finish free from pits and dimples has less stress risers that may increase the risk of cracking. Yet many customers also want rocker arms that look great, with a colored anodized finish or a polished appearance.|
Chris Douglas at Comp Cams said his company’s new Ultra Pro Magnum rocker arms, which were introduced at this year’s SEMA show in Las Vegas, is a modern arched, web-like design that delivers increased strength and rigidity with less weight. “We completely redesigned these rocker arms from scratch using the latest design technology,” said Douglas. The new rockers are made from 8650 chromemoly steel rather than aluminum, and are approximately 29 percent stronger than the previous Pro Magnum rockers. The rockers have oversized trunions, precision-sorted needle bearings, hardened roller tips, and are rebuildable. They are also guaranteed against breakage for life, and have a black oxide finish to resist corrosion. Applications include SB/BB Chevy, and Ford 289-302-351W V8s.
Crane Cams will be introducing some new shaft-mounted rocker arms at this year’s Performance Racing Industry (PRI) show, but would not reveal any details prior to the show. Roger Vinci, Crane’s manager of new products, said Crane currently manufactures five different styles of rocker arms, including Pro Series L92 rockers for the Chevy LS engines. "Our Pro Series rockers are lightweight, compact and durable, and use our Quick Lift geometry to maximize valve lift for a given camshaft profile."
Vinci said Crane uses a unique surface finishing process on their rocker arms. The Mikronite process is similar to shot peening but is done in a centrifuge with media that hits the surface of the metal with 40 to 70 G’s of force. This improves the compressive stress of the rockers but does not change their hardness. The result is a nice chrome-like polished finish that is more than cosmetic because it significantly increases the strength of the part.
Rick Simko at Elgin Industries said his company’s line of extruded aluminum rockers provides good value for the Saturday night racer. “Our approach is to offer rockers that provide the best cost effectiveness for going fast. Our rockers provide a good combination of light weight and strength, and have nitrited roller tips to improve durability.” Simko said Elgin doesn’t have any new rockers to talk about, but has expanded its valve spring line with 20 new part numbers.
Randy Becker Jr. of Harland Sharp Custom Speed Parts Mfg. Co. said his company continues to refine its Original, Heavy Duty and Diamond Series rocker arms. The Heavy Duty rockers are designed for applications with high spring pressures, while the new Diamond Series is for applications that want the lightest possible rocker. The Diamond Series are available for SB/BB Chevy and SB Ford engines, are over 100 grams lighter than Harland Sharp’s Original roller rockers and are machined at 45 degrees in low stressed areas to remove weight.
Becker said his company has new rockers for the Chevy L-Series engines including LS7 and L92, and is also doing some new rockers for diesel engine applications. “We also have new shaft mounted rockers for various aftermarket cylinder heads.”
Becker said all the rockers Harland Sharp currently produces are aluminum, but may be looking at some steel rockers for certain applications down the road.
Rob Remesi of Jesel said his company is introducing shaft-mounted rocker arms for the new 5.7 and 6.1L Chrysler Hemi engines. The new Hemi is finding its way into many racing applications, but the stock valvetrain can’t handle high lift cams and stiffer valve springs. Jesel’s solution is a new CNC-machined out of 7000 series shot peened aluminum. The new rockers will easily clear springs up to 1.450" in diameter, and can handle open spring pressures as high as 600 lbs.
To reduce friction, .250" wide needle nose rollers are used on valve end of the rocker arms. Available rocker ratios include 1.50, 1.60 and 1.70. Cylinder head machining is necessary to install Jesel’s new shaft rocker system. The block must also be converted to roller lifters with conventional pushrod type oiling, and the multi-displacment system must be eliminated.
Luke Whalen at Scorpion Performance said his company is introducing a new Platinum Series of aluminum rocker arms. The rockers have been computer-designed to minimize weight and maximize strength.
“The new Platinum Series rockers have a raised spine to improve stiffness, yet are 20 grams lighter on the roller side and 14 grams lighter on the pushrod end to minimize weight,” Whalen said. “The rockers are designed to handle up to .950" lift, open spring pressures up to 950 lbs., and springs up to 1.625" in diameter. The new rockers are available in a wide range of ratios.”
Whalen said the Scorpion Platinum Series rockers are manufactured by automated machinery, then hand polished, anodized, clear coated and laser etched to give them their unique appearance.” The rockers also have a lifetime warranty. Whalen said Scorpion currently is not doing any steel rocker arms, but has a line of titanium rockers for extreme racing applications.
Phil Elliot of T&D Machine Products said 75 percent of his company’s rocker arms are custom-made for performance engine builders. “Last year we introduced a new line of lightweight steel rockers for exhaust valves. We now have steel intake and exhaust rockers for almost every application we do, from stock ratios up to 2.0 and higher. We’re making steel rockers for NASCAR teams, LS3, LS9 and L92 Chevy engines, even Edelbrock’s new 409 cylinder head. We still do aluminum rockers, but in most cases our steel rockers are actually lighter than our aluminum rockers.”
Elliot said racers like steel rockers because they provide better fatigue strength than aluminum, and they can absorb more abuse. “Most Cup teams used to replace their rockers after every race. With our steel rockers, many teams are using the same rockers for three or four races.
“Something else we do is route oil from the pushrod cup in the rocker to the valve spring. Oiling the spring helps it run 60 to 70 degrees cooler so the springs will last longer.”
As for new products, T&D introduced a new “eccentric” rocker set at last year’s PRI show that uses an eccentric on the rocker shaft to set valve lash rather than an adjustment screw on the rocker. Getting rid of the adjustment screw reduces the weight of the rocker.
In recent years, there has been a flood of no-name, low priced aluminum rocker arms coming into this country from elsewhere in the world. As with all of the other engine parts, some of these are quality products that provide good value for the budget-conscious engine builder. Some are, in fact, brand name products that are manufactured to domestic specifications overseas. But some are not very good quality. Problems include failure of the needle bearings and rollers as well as cracking and breakage. Worse yet, some of these low-quality rockers are outright copycat counterfeits of name brand products.
One brand name rocker manufacturer said many of these fake rockers have been sent back to them under warranty. “They are not our rockers. We did not manufacture them, nor did we sell them. But people who bought them don’t know that, and they want us to reimburse them for the failed rocker arms. We’ve had a couple hundred of these claims, and it is hurting our reputation.”
The best advice we can give our readers is to buy brand name rockers either directly from the manufacturer or through a reputable distributor. If somebody tries to sell you a set of no-name rockers with no warranty, or a set of “brand name” rockers at an unbelievably low price, watch out. The rockers may be fakes!
As rockers continue to evolve, the ongoing trends toward lighter weight and stronger designs will continue. Many rocker arm manufacturers also offer custom rockers, as well as a wide range of ratios and rocker styles (stud mount, pedestal and shaft mount).
Higher quality finishes on rocker arms has also become the norm rather than the exception. A polished finish free from pits and dimples has less stress risers that may increase the risk of cracking. Yet many customers also want rocker arms that look great, with a colored anodized finish or a polished appearance. You can’t see the rockers when the valve covers are installed. But when the covers come off, the rockers really stand out.
Everybody seems to want lighter rockers, too, though lighter isn’t necessarily better if the application requires extreme strength. A slightly heavier steel rocker may actually be better. Reducing the weight of a rocker arm reduces its inertia, allowing the engine to rev quicker and higher. This can be done by making the rocker arm thinner or by using a lighter metal such as aluminum or titanium. But the rocker arm must also be strong enough to withstand the loads imposed upon it by higher rpms and open spring pressures. So engine builders have to consider all the variables when choosing a rocker arm.
For a low budget Saturday night stock car engine, price is probably more important than weight or strength. A budget-priced rocker arm that provides better performance and less friction than a stock rocker arm would be a good upgrade. But for a ProStock drag car, a premium rocker (steel, aluminum or titanium) that offers ultimate strength and durability would be the best choice.
Another consideration is how the rockers are mounted in the cylinder head. At higher spring pressures, stud mounted rockers may break the studs. Installing a stud girdle over the rockers can extra support and rigidity. But a girdle gets in the way, and also requires taller valve covers.
Shaft mounted rockers, by comparison, don’t need a girdle because the shaft provides rigid support. The shaft also holds the rockers in perfect alignment, eliminating the need for a pushrod guide plate. Shaft-mounted rockers reduce flex in the valvetrain at high rpm for better valve control. The shaft can also supply oil pressure to the rockers to improve lubrication, and reduce friction by lowering the pivot point of the rockers slightly with respect to the valves and pushrods.
Rocker arm ratio is another variable that needs to be considered. Why go with a stock ratio if you can get more lift and performance with a higher ratio rocker? A higher ratio rocker gets more valve lift out of a given cam profile. A higher ratio rocker lifts the valve off its seat at a faster rate to increase airflow without changing duration. For a street performance engine, high ratio rockers can add horsepower with little or no loss in low rpm torque, idle quality or vacuum. In a high rpm racing engine, high lift rockers also reduce the amount of lifter travel needed to open the valves. This reduces internal engine friction and the inertia of the lifters and pushrods. It also makes it easier for the valve spring to close the valve and overcome the weight on the pushrod and lifter side of the rocker arm because of the leverage effect. But really high lift ratios require a very strong rocker arm design.
One thing to keep in mind with higher ratio rockers and stiffer springs is the load on the pushrod. Most stock pushrods can’t handle open spring loads over a couple hundred pounds. Install a set of double springs with open seat pressures over 600 lbs., and you’ll bend pushrods unless they are replaced with thicker wall and/or larger diameter pushrods to rigidity. On many engines, the size of the pushrods is restricted by the guide plates on the cylinder head, so the only option is to go with thicker wall pushrods.
Last year, Schumann Sales & Service introduced its new “bimetal” aluminum/steel pushrods. These pushrods are a .065" thick chromemoly steel pushrod with an inner aluminum tube that adds stiffness without adding much weight. Vern Schumann says his bimetal pushrods are three times stronger than a standard chromemoly pushrod, and 30 to 40 percent lighter than a comparable thickwall pushrod. He also says the inner liner in the pushrod also speeds oil flow to the rocker arms for better lubrication at high speed.
This year, Schumann is introducing a thickwall pushrod with one-piece forged ends that is an affordable alternative for budget racers who want to upgrade their pushrods but can’t afford premium pushrods. The new pushrods are a .065" thick chromemoly rod that can handle spring pressures to 650 lbs.
Stiffer valve springs are needed for higher rpms, but the design of the spring is just as important as the pressure it exerts. Spring harmonics can cause weird things to happen in the valvetrain at various rpms, so a spring should be designed to minimize harmonics as much as possible.
In recent years, “beehive” springs have caused quite a buzz. Chevy LS1/LS7 series engines use a factory beehive spring, as do Ford modular 4.6L V8s. The springs are tapered in toward the top. This allows the use of a smaller and lighter spring retainer, and it also improves the harmonics of the spring. The smaller coils at the top of the spring create a variable spring rate, which is different from the linear spring rate of a conventional valve spring.
The only drawback to the beehive design is that you can’t fit one spring inside another for a double spring setup. Many racers don’t like this because it increases the risk of engine damage if a spring breaks. With a double spring, the second spring will help prevent the valve from dropping into the cylinder if the other spring breaks.
Some manufacturers are using more “ovate” wire in their springs instead of round wire. The oval shape of the wire is more durable and less vulnerable to cracking and failure.
Some manufacturers also use various surface treatments to improve spring durability. This includes shot peening, applying various types of surface coatings to manage heat, and cryogenic treatments. Freezing springs to several hundred degrees below zero changes the molecular structure of the spring, and helps relieve stresses that may cause the spring to weaken or crack. The result is longer spring life and more consistent pressure for the life of the spring.