The differences between 8620 and 5160 steel core camshafts and why it’s so important
Words Jeff Smith Photos Comp Cams, Jeff Smith
BILL JENKINS WROTE
a book in 1976 with Larry Schrieb, entitled The Chevrolet Racing Engine. This soft-cover book became the bible for thousands of enthusiasts who wanted to learn about building a high-horsepower drag race small-block Chevy. Much of the information from that book is still useful today. Among the thousands of bits of information was a reference to 8620 steel core camshafts. This was nothing new in the cam industry, but few casual enthusiasts knew about this high-performance cam core. For some, little has changed in nearly 40 years and there are many engine builders who claim that the 8620 steel core camshaft is the only way to build a race-oriented or even a hot street-performance camshaft. Lately there have been many discussions on forums and message boards about the differences between 8620 steel “gold core” cams and “black core” 5160 steel billet cams. Much of the opinions offered in these forums contain barely a sliver of actual fact. 40 Power & Performance News / Vol. 6, No. 2
This story weaves a tale that involves a little bit of metallurgy, a touch of heattreat technology, and an approach to building a quality camshaft core that will do the job without a lot of drama, and might even save you some money. In talking with COMP’s Scooter Brothers, he explained that for multiple decades, most mechanical roller cams were built on 8620 cores and worked relatively well. Cam failures that did occur were often traced to issues with cam spalling, which is damage to the surface of the lobes. Scooter says that about 30 years ago COMP commissioned an investigation to evaluate a better way to build a high-performance steel billet camshaft. The study employed metallurgists, heat-treating experts, engineers, and other sources who eventually revealed these cam problems were traced to issues with the depth of the heat-treat. The issue with making a camshaft core is to build it with a surface finish hard enough to resist wear, yet retain
ductility (the ability of the steel to bend rather than break), and also be able to be machined easily. These differing requirements are often at odds with each other. For a long time, 8620 alloy steel billet camshaft cores met these tasks most of the time. But as valvetrain inertia loads have increased as engine speeds and power levels escalate, more problems with the 8620 core have surfaced. Nearly all of these problems can be related to the heat-treat process. Another part of this investigation revealed that there was a better way to create a more consistent heat-treat. Specialty, high chromium alloy steels have become the answer for high-stress engine applications like NASCAR and sports car racing, but these camshafts are also expensive, often between $2,000 and $3,500 apiece. For Sportsman racers, these solu-