While lying on an exercise mat doing sideways leg lifts, I noticed something. It takes some concentration to lower the lifted leg in a controlled manner so it doesn’t bounce a couple of times after hitting the other leg.

I am made of soft, self-repairing protein soup, but valves are made of much more rigid metal that cannot long survive hard seating impacts as they close. To prevent outright valve breakage or seat recession, valve seating is controlled by a seating ramp, ground as part of the cam lobe, limiting the final approach of the valve to its seat to roughly one foot per second.

Even so, valves in racing engines are known to bounce after seating as many as three or four times. They bounce because, like a child’s rubber ball, valves are elastic. As the seating surface of the valve head hits the seat and stops, the rest of the valve keeps moving, momentarily deflecting the valve head into a slight cup shape. The next instant the energy stored in that deflection snaps back, causing the valve to spring back off its seat—a bounce. Think of the valve head as analogous to a trampoline and the stem as the person enjoying the ride.

The goal is to achieve valve-train stability at higher engine rpm, possibly translating to races won.

Detailed information about valve-train behavior has come from Spintron studies. The Spintron is a system that drives with an electric motor an engine’s valve train while measuring valve position, velocity, and acceleration to very high accuracy using laser interferometry.

Spintrons are especially active in NASCAR racing, where large V-8 engines with complex pushrod-and-rocker valve trains must somehow be kept together at more than 9,000 rpm for 500 miles. NASCAR engineers work hard to learn everything about all the parts in their systems—how much pushrods compress and rockers bend, how valves waggle from side to side as various rocker geometries subject their stems to side forces. The goal is to achieve valve-train stability at higher engine rpm, possibly translating to races won.

V-twin homologation special
More than a decade ago, Ducati introduced the 1098R, the company’s V-twin homologation racing special. “The eye darts first to the gold-colored oversized beryllium-copper valve-seat rings,” the author wrote, “a necessity for use with titanium valves.”Ducati

Another area in which valve seating velocity is a big issue is in the development of valve-drive systems not based on cams but rather moved by such means as electrical solenoids or hydraulic or pneumatic pistons, their movements controlled by computer.

Although the opening and closing timings of cam-controlled valve drives can be altered by electric or hydraulic cam phasers that advance or retard a cam as a whole, they cannot vary valve lift or open time. Variable valve lift and duration are the hoped-for payoff from the various proposed non-cam-driven systems.

Systems now under development are able to vary lift and timing under computer control, to give an engine Harley-Davidson-like torque down at 1,200 rpm yet also display GSX-R-like cylinder filling at higher revs.

Their problems so far have been cost and reliable control of valve seating velocity. While it’s understandable in this smartphone age to expect Ted-talking technocrats to solve such problems with a snap of their fingers, cams remain on the job throughout the motor-vehicle industries of the world.

Which notional change will happen first? Will non-cam-driven valve systems revolutionize the internal-combustion engine? Or will wonderfully improved inexpensive electric vehicles force the IC engine right off the market? Mesdames et messieurs, place your bets.