I’m embarrassed. As many years as I’ve been sitting in this chair, everything I really know about cams could fit in a few paragraphs. When I say “really know,” I’m not counting time-honored myths or threadbare anecdotes—just the cold, hard, dyno-proven facts. Some stuff I’ve learned along the way: a roller beats a flat lifter every time, bigger isn’t always better, beehive springs work, great cylinder heads fix everything, and there’s big power lurking in narrower-than-catalog lobe separation angles. That’s not a lot to show for 19 years behind an editor’s desk, but compared to what our grandparents knew about cams, it’s indistinguishable from magic.
Years ago, I had the pleasure of taking a tour of the Henry Ford Museum in Dearborn, Michigan. If you’ve never been there, you need to make the pilgrimage. Among the many fascinating things there were examples of early internal combustion engines. In the beginning, there were no preconceptions about how engines should be designed—everything was approached with a blank sheet of paper. At the turn of the 20th century, any idea was game, and things we take for granted today, such as spark ignition, cam-actuated valves, and throttle plates, were far from the norm. Take compression ratios, for example. Did you know that the idea of compressing the air/fuel mixture was not even firmly established? Some early two-stroke engines leaked fuel into a combustion chamber at atmospheric pressure.
Another kind of engine called the hit-and-miss was very popular until the 1930s, and didn’t have a throttle body at all. Engine speed was controlled through a governor that kept the exhaust valve open until the engine speed fell below a predetermined level. They sounded like “whoosh, whoosh, whoosh, pop!” These days, we use a simple throttle plate to control engine speed. Nevertheless, diesel engines still eschew the throttle plate, instead choosing to take advantage of the efficiency that comes from reduced pumping losses.
One of the more interesting engines I remembered seeing had a camshaft only for the exhaust valve. The intake poppet valve was continuously held closed with a lightweight spring, only opening when the vacuum in the cylinder was sufficient enough to suck it open! Cam timing and lift on the intake side were literally determined by valvespring pressure. Go ahead and laugh, but at the time it was considered a very elegant solution. You had half the number of moving parts in the valvetrain, making it simpler to build, cheaper to buy, and easier to maintain.
Before the 1950s, compression ratios were considered low by today’s standards, and rarely exceeded 7:1. That’s significant because until CRs rose, performance camshafts—at least for the masses—couldn’t exist. Indeed, it was a half century into the IC engine’s development before pioneers like Ed Winfield, Ed Iskendarian, and Harvey Crane could begin to take advantage of the power hidden within the camshaft. Once real compression happened, we all fell in love with cams.
Most Internet experts think they’ve got a pretty good handle on camshaft theory, just ask them—they’ll confirm it. While the camshaft is not the most complicated thing going on inside a hot rod, it’s probably the most glamorous, and that’s why it’s so near and dear to us. Reality is, the “experts” focus too much on the cam spec numbers, and not the actual event timing or the concept of expansion ratio—the two most important ideas. Having seen the light—and subsequently having been blinded by it—I realize I don’t know that much about cams.
My simple solution on picking a cam is to ask someone who’s built a bunch of really successful engines similar to the one I’m building. This gets me in the ballpark, albeit without really knowing why it works. Nevertheless, I’m drawn irresistibly to the inner workings of camshafts. Why is the intake valve closing event so crucial? How come the power curve changes so dramatically with a tightening of the lobe centerline angle? What the hell is jerk? After all these years, camshafts are still a black art for most gearheads, even to “experts.”
Fact: The gasoline engine is only about 20 percent mechanically efficient—and that’s after over a century of work. This means there’s lots of room for improvement, and the camshaft (or perhaps the lack of one!) will have a big part to play. When those breakthroughs happen, we’ll be there to report them. In the meantime, kick back and enjoy our camshaft-packed issue!