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How To Increase Engine RPM - How It WorksModern race engines turn 9,500-plus rpm with ease, and here’s how they do it From the November, 2011 issue of Chevy High Performance By Stephen Kim
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It’s all about rpm, baby. In just about every racing class in existence that limits maximum displacement, the quest to turn more rpm than the next guy rules the day. In classes where power adders are prohibited, it’s quite easy to understand why this is the case. Once an engine builder has squeezed every last cfm out of a cylinder head, and torque output plateaus, the only way to increase horsepower is to turn more rpm. For proof, you needn’t look farther than an 11,000-rpm NHRA Pro Stock motor, or the 9,500-rpm mills in NASCAR Sprint Cup. The most extreme example of the importance of rpm is in Formula 1. Not long after the sanctioning body cut down max displacement to 2.4 liters in 2006, engines started spinning up to 20,000 rpm. Consequently, now in F1 there’s a cap on both displacement and maximum rpm. As impressive as those lofty revs may be, the use of pneumatic valvesprings in F1 motors makes them difficult to relate to for 99.9 percent of hot rodders. In some respects, it’s much more difficult to turn half as many rpm with mechanical springs. To learn the intricacies of building an ultrahigh-rpm valvetrain, we contacted some of the best in the business. Our panel of experts includes Judson Massingill of the School of Automotive Machinists, Darin Morgan of Reher-Morrison, Phil Elliot of T&D Machine, and COMP Cams. Follow along as we show you how to give your tach a beat-down. Judson Massingill: Valvetrain technology has gradually progressed over the years, addressing one weak link after the next. In the late ’80s, we had the ramp technology built into the cam lobes that would have enabled the level of rpm engines are turning today, but we didn’t have the valvesprings to control them. Then by the early ’90s, the valvesprings were much improved, but the lifters started breaking due to all the additional spring pressure. Typically, the axles for the roller wheels or the axle supports were the first area to fail. To address this issue, the aftermarket came out with true race lifters that moved the limit of rpm back to the springs. At this time, the valvespring and lifter technology were adequate for the rpm motors were turning, but racers being racers, they always tried to wring a couple of hundred extra rpm out of their motor. If a company like COMP Cams tested a valvetrain to 9,000 rpm on a Spintron, sure enough, racers would spin their motors to 9,200 rpm. At this point, the weak link became the rocker arms. The stud-mounted rockers of the day just weren’t able to handle the spring loads and rpm that race motors demanded. Once again, the aftermarket responded by developing shaft-mounted rocker arms. Shaft-mount rockers were around long before this time, but they weren’t really necessary because we didn’t have the spring and lifter technology to take advantage of them. With the rocker issue solved, that put the rpm limitation back on the valvesprings. As you can see, it’s not a single component that’s responsible for what has enabled modern race engines to turn more rpm than anyone could have imagined just 5 to 10 years ago. It’s a tapestry of elements that had to come together to make it happen.
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