When building an extreme performance small-block, each valve train component is critical to accurately transfer the engine’s breathing instructions from the camshaft to the valves. The oversized 60 mm camshaft in the 440 cubic-inch LSX that we’re building resists flex to maintain accuracy down to the degree as they’re transferred into the lifter. Large .903-inch diameter body lifters are dropped into fully bushed bores to encourage smooth and accurate timing events. Then, massive 1/2-inch pushrods are used to over-power equally massive 430-pound spring rates that allow the valves to inhale and expel air as they cycle upwards of 10,000 times per minute.
One of the most critical pieces of hardware in translations of cam instructions to valve events is the rocker arm. For our build, when it came to selecting a rocker arm that would be up to the task, we didn’t want to get it wrong, so we turned to one of the most familiar names in the industry: T&D Machine Products.
As we originally hinted in our induction piece, The Anatomy of a Full Race Radial 275 Induction System, T&D Machine Products specializes in shaft-mount rockers designed specifically for high-stress or high-endurance race applications, from drag to stock cars. Because we couldn’t get this critical piece of the engine wrong, we consulted with Phil Elliott and Sheldon Miller at T&D to help us learn how rockers are made, and what to look for when selecting the proper rocker for a given combination.
“If you look back to rocker arm design in the 1940s, Oldsmobile and Cadillac had shaft-mount rockers with adjustable tips. By the time the small-block Chevy came along, GM realized they needed the ability to produce rockers by the millions,” Elliott says.
“When you’re starting from scratch, a stud mounted rocker doesn’t make sense.” – Phil Elliott
“Stamped-steel rockers work okay and even hold up to some performance applications, but once you get a sizable cam in the engine, it’s going to cause problems and eventually rip the studs out,” Elliott noted. As a solution, many enthusiasts turned to fulcrum bearing rockers and screw-in studs, but that still came with a host of problems.
“Look at all the components you need to install an aluminum stud-mounted rocker on a small-block Chevy,” Elliott says. “You needed a screw-in stud, so you had to machine the bosses down and install the studs. Then, after you got the rockers installed, you needed a girdle to keep them somewhat supported, which made servicing take longer. After all that, you still needed special valve covers to clear everything for a solution that didn’t offer the stability provided by a shaft mount system.”
Contrary to a stud-mounted rocker, T&D’s shaft rockers mount to a shaft and then to a billet one-piece stand that distributes the forces exerted by the rocker across the head, rather than into a single stud. The result is a rocker with more fasteners that’s anchored on both sides and resists the side loading that can take place with the single stud-mount design. This is critical in high performance applications where improper geometry can lead to bad timing events, premature wear, and in some cases, engine failure.
Stamped-steel rockers work okay and even hold up to some performance applications, but once you get a sizable cam in the engine, it’s going to cause problems and eventually rip the studs out. – Phil Elliott
From late model to exotic and even class-limited head limitations, T&D has prototyped many different rocker designs that required the accommodation of varying valve layouts and cam designs.
In our case, this is a very important distinction, as the Mast Mozez head is a canted valve head with significantly altered valve placement. Contrary to a standard inline head where the valves are parallel to each other, a canted head angles the valves away from their respective cylinder wall and points them towards the center of the bore. In addition to reducing the shrouding effect, canting the valves allows the head to accommodate a large valve without running into cylinder wall interference.
The net effect is a larger, more efficient air passage to the cylinder. However, this also means that the valves are arranged in such a fashion that many of the valvetrain components need custom fitment. The flexibility in placement of a shaft-mounted rocker allows us to make less dramatic changes elsewhere in the engine. As Elliott explains, “you have this extreme LSX head where they’ve moved the valve. Sure, we could take some of our common [rocker body] extrusions, but for the most part, we have to start with the layout and design from scratch.
“We have a coordinate measuring machine (CMM) where we can pick up a bunch of points from the cylinder head and digitally draw it in CAD,” he continues. “From there, an engineer can build a rocker arm in the computer without ever touching a machine.”
In addition to new designs for mass production, T&D also works with teams to produce limited runs of one-off parts. For this process, they utilize a 3D printer in conjunction with their CMM software. Together, the package allows them to draw, print, and then test-fit parts through one or more iterations before spending resources on tooling and material on parts that need a custom fit. The process also saves the company time in development, as the process of printing a part, testing fitment, and then moving some lines in AutoCAD and reprinting it is much quicker and cheaper than tooling up a CNC.
In our case, we were able to print custom stands to check fit before milling them from expensive steel. Through the use of technology, T&D is able to bypass some of the initial tasks that prove to be tedious and get a headstart on custom fitment. After digital mockup, new designs go to an in-house machinist that focuses on taking the virtual designs, converting them to real hardware, and then modifying the rocker in the real world to verify proper fitment before a new design can be loaded into the CNC machine and go into production. “It’s very necessary. A computer doesn’t care what line you draw … a tool is going to follow it,” Elliott says.
We ended up with a really trick set of steel roller-tip shaft rockers that were made from the ground-up specifically for Mast’s Mozez head. We were fortunate that shops like Pro Line Racing had already worked with T&D on rockers for this cylinder head in combinations like Keith Berry’s 4.0-second Pro Drag Radial Corvette, which has been in the three-second zone with its twin-turbo LSX combination.
What about the specs? We went with 1.85 intake and 1.80 exhaust ratios that translate the respective .515 and .510 lobe lifts to almost a full inch at the valve. Specifically, the math put us at .953 lift on the intake and .918 on the exhaust. “We put the 3D printer to use and reworked the stands for increased lifter and pushrod clearance. When completed, the finished steel rocker body is not much heavier than its aluminum counterpart, but comes with a substantial strength increase,” says Elliott.
“Our aluminum is proprietary and so is our steel,” he continues.
These rockers will be under tremendous amounts of pressure as they transmit cam movement across the valvetrain and through the spring. In addition, the 1.85 and 1.80 ratios mean rockers will add lift to the cam profile by multiplying cam movement from as little as one and a half to as much as two times the lobe lift. With the multiplied lift and the countering spring pressure, race engine rockers are under a lot of stress and sometimes fail.
To prevent premature failures, T&D worked with suppliers to source better raw materials for their rockers. “Aluminum has a memory which causes wear and limits the life of the rocker. Fifteen years ago it was discovered that the available alloys were not up to the task, so we worked with our supplier and blended our own proprietary alloy for greater longevity and elasticity,” Elliott says.
But they didn’t stop at the materials. As a favorite among NASCAR Sprint Cup racers, T&D was able to utilize Spintron data to strike a balance between weight and strength. Simply explained, if a rocker meant to run 500 miles could last 1,500 miles, it can be lightened. Equally, if a rocker meant to last 500 miles only lasts 400 to 600 miles, it needs more strength and likely more weight. It’s when the roller hits the valve stem that you really know how a rocker is going to perform. With this data, they’re able to provide improved and predictable rocker performance before there are failures on the track.
“A rocker is a pry bar. If you have a piece of aluminum running through a million cycles and then hundreds of heat cycles, you will eventually have problems. It’s not if, but when, and we have a way to check that,” Elliott states.
A rocker is a pry bar. If you have a piece of aluminum running through a million cycles and then hundreds of heat cycles, you will eventually have problems. – Phil Elliott
T&D recommends that customers send in their rockers every one to two seasons for inspection and maintenance, depending of course on the number of runs or laps the rockers have gone through.
From 200-plus mph blasts down the 1/4-mile to 500 laps races around the oval, T&D has or can build a rocker that will fit your application. In our case, they were able to set us up with a stylish but functional rocker system that’s strong as steel, as light as aluminum, and won’t leave us at the announcer’s booth looking for a replacement between rounds.