The ever increasing spring pressures and rpm rendered 86 materials unacceptable, especially as lobes were made more narrow to accommodate their relocation.
Not only were cam diameters growing but the materials were evolving from a surface hardened cast iron to tool steel. Once the aftermarket block manufacturers realized this was the direction serious race motors were headed, they put more material in the bearing bosses so they could be bored to fit the largest cam cores available. So, the lesson learned was that a larger diameter cam core with more lobe lift and less rocker ratio was smoother and easier to rotate than a smaller cam core with higher rocker ratio. In a NHRA Pro Stock motor that runs 1350psi open spring pressure that would amount to 432-pound static force reduction – on one valve! Multiply that by 16 valves and 10,000rpm and you get a better picture of the gains in durability and force (hp) required to rotate that high rocker ratio valvetrain. A 2.00 ratio rocker places approximately 33% more load on the lifter, pushrod and camshaft than a 1.50 ratio rocker. When you look at the numbers, it is easy to see Dan’s logic. However, that required a larger diameter camshaft core with larger bearing diameters. Dan’s idea was to take the ratio and load off the rocker and put the lift back on the cam lobe. The traditional high rocker ratio technology would allow racers to flirt with the 10,000rpm range, but above that valvetrains had a way of self-destructing. At the time Dan was working on a program to stabilize a NASCAR Xfinity engine valvetrain above 11,000rpm.
While this was going on, Dan Jesel was running in the opposite direction – he was looking for ways to reduce rocker ratio to take load off of the valvetrain. Engine builders and racers were “pushing the envelope” with rocker ratios over 2:1 and as a result, valvetrain stability and durability were going downhill fast. Unfortunately, cam lobe lift had been maxed out for a number of years and the only way to achieve more lift was with higher rocker ratios. As aftermarket cylinder heads evolved with much larger ports and bigger flow numbers, it became apparent that increasing valve lift would result in more power.
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