The rocker arm is one of the...
The rocker arm is one of the most important components in the linkage between the camshaft and the valves. In a race motor, the geometric and component design can offer gains in efficiency and horsepower.
To call the Crane Cams shaft-mounted "Quick-Lift" design rocker arms new would not be entirely accurate. To say they have burst onto the scene and have created a lot of excitement among high-performance engine builders would be more true.
This concept has been contemplated and fiddled with for a long time, beginning with Smokey Yunick and his accomplished assistant, Ralph Johnson. Let's face it. Smokey fiddled with every component on the engines, but he thought there was really something to be gained with the geometry of the rocker arms. Ralph now works in the secretive R&D division of Crane Cams and has been instrumental in the development of this design from the very beginning.
The reason this particular design was so late in coming is the technology of materials and the design equipment needed to build and test these new rocker arms had not yet been invented. A lot of engineering, research, and development went into the current design. It didn't just pop out of the CNC machine and go to market-not by a long shot.
Ralph Johnson worked with...
Ralph Johnson worked with Smokey Yunick to develop better geometry for the common rocker arm. That early work has paid off and can now be utilized by all racers due to advances in materials and machinery.
The new design has several cutting-edge features that are attractive for high-performance applications. The first feature we will talk about is the material itself. The rocker is made from a special alloy of aluminum that is stronger in the heat range in which it must perform.
A New Material Years ago, major aluminum companies developed high-strength aluminum products for the aerospace industry. The operating temperatures that an aircraft encountered, for design purposes, were from 100 degrees F all the way down to subzero temperatures. This heat range was at the opposite end of the spectrum from that experienced in racing applications. Modern racing engines operate in the range of 250-300 degrees F.
When Crane design engineers first asked for data on aluminum's strength at higher temperatures, the companies that produced high-strength aluminum did not have any information to share. Subsequently, the top suppliers of special alloy aluminum tested and developed compounds that were actually stronger in the higher heat ranges than at ambient temperatures. Crane now utilizes those aluminum compounds in the manufacture of their rocker arms.
The new rocker body is made from an extruded billet of a new alloy variation of 2024 grade aluminum that has only recently become available. According to the company's claims, it is "approximately 30-percent stronger at 300 degrees F than other comparable alloys.
The Spintron test machine...
The Spintron test machine has allowed Crane Cams to efficiently develop new valvetrain components. Here, the new Quick-Lift rocker arms get a workout through simulation runs for Dragsters, Sprint Cars, and Stock Cars. The unit's "Laser Valve Tracking System" was ideal for testing the rockers.
Advanced Geometric Design The installed ratio, or what I will call the "net rocker ratio," or NRR, is determined by measuring the travel of the valve divided by the travel of the valve lifter as the cam cycles through its motion. When we know this ratio, we truly know what the rocker is doing throughout the cam rotational cycle. The measurement of the distance from the centerline of the rocker shaft to the tip of the pushrod and then to the end of the valve stem does not represent the true picture of rocker ratio.
The measured effective rocker ratio (measured at the rocker), or ERR, must take into account the angle of the valve stem and pushrod-to-rocker arm alignment. If these angles become more or less than 90 degrees throughout the cam cycle, and that is exactly what happens, then the ratio is necessarily changing.
In order to determine the true rocker ratio, you must measure, in increments of degrees of camshaft rotation, the travel distance of the valve divided by the travel distance of the lifter. This ratio can and does change in most applications.
Depending on the design and construction of the rocker arm, the ratio can start out less than the "advertised," or stated ratio and then reach the stated ratio at mid-cycle. On the back side of the cycle, as the valve is closing, the ratio decreases until the valve is closed. This type of design offers less flow of air/fuel mixture during the whole event.
Another design might have the true rocker ratio start and end, through the whole cycle, at the stated ratio for the rocker. This represents an improvement in rocker arm design, but the Quick-Lift design has been shown to be even better than that.
 The new alloy of aluminum...  The new alloy of aluminum that the rockers are made of has demonstrated increased strength at higher temperatures (between 250 and 300 degrees). This is an improvement over previous grades of aluminum that were designed for much lower subzero temperatures. |  The valve tip and the pushrod...  The valve tip and the pushrod tip of the rocker follow arcs as the cam lobe goes through its cycle. This effectively changes the NRR, as measured in the movement of the lifter versus the valve |  The geometry design of the...  The geometry design of the Crane Cams Quick-Lift rocker arm increases the net rocker ratio (NRR) at both ends of the valve opening cycle. This is done by carefully measuring and designing the relationship of the contact angles to the pushrod and valve at each phase of the cycle. |