One of the favorite topics of engine builders is that magical stick called the camshaft. The specs held within its shape control the action of the valves and hold the promise of more horsepower, better mileage, higher rpm, or a meaner sound. There is truth to these beliefs—you might say nothing will determine an engine’s “personality” more than the camshaft. It is also true that the right choice in selecting a camshaft can make or break an engine build. So how do we go about making the right choice?
Some guys will straight up argue that there is one “correct” grind for a given engine combination. I think there may be some truth to that if you can define the characteristics that make the selection “correct” in the first place. The most likely definition here is power output, probably over the entire usable rpm range of the engine. I guess a perfect example is the engines run in the AMSOIL Engine Masters Challenge. Here, the engines must make maximum power over the entire operating rpm range, and cam choice becomes a critical contributing factor. The adherents to the “correct” cam school of thought can identify with the idea of maximizing power at every point of the rpm range, however, I question whether that should be the end of the discussion.
According to the “correct” cam gurus, the ideal cam can be selected on the basis of plugging engine specification parameters into a computer model, and the perfect camshaft for that engine will be dutifully derived. My question with the logic here is, “Perfect for what?” I contend that cam selection is a more nuanced process, taking into account and balancing the many factors involved to meet the end objectives of the engine builder. Want an example? Take the modern Chevy LS7, an OEM engine that is unquestionably powerful as delivered, but with a simple cam change, capable of significantly increased output. Would the “correct” cam guys argue that GM clearly missed the mark when spec’ing the cam? After all, a cam swap alone will unleash plenty more power.
The fact is, the engineers at GM worked toward multiple goals when selecting that particular grind. The engine’s idle smoothness, fuel efficiency, and durability no doubt played as important a role as outright power in determining the production grind. Striking that balance to achieve the desired operating goals is ultimately what will make you happy with the engine. The fact here is that those operating goals are going to vary widely.
As the engine builder and perhaps ultimately the user of that engine, the first step in the cam selection process is to define what your goals are for the project. I received a letter from a reader recently looking for a cam recommendation, whose goal was a “crazy radical” idle in a nearly otherwise stock engine. This guy was very specific, spelling out clearly that driveability, vacuum, economy, and even peak power output were no concern. With that as the only criteria, it was pretty easy to meet his request with a long duration, slow lobe profile on tight centers with a big exhaust duration split and with low peak lift to work with the restrictions imposed by the heads.
This is not a combination I would want to run, but then I wouldn’t select a cam just on the basis of producing a “crazy radical” idle. In fact, for street performance, I tend to be on the conservative side compared to some, placing more weight on durability and reducing spring loads, efficiency, and idle quality. Sometimes that is enough to get some of my big-cam buddies to make fun of my “baby” cam specifications. Still, with right cylinder head/induction/cam combination to meet the intended rpm range of the bottom end and valvetrain, along with a matched compression ratio, you’d be surprised how much you can pull back the cam specs without giving away power. The bottom line, I guess, is when it comes to spec’ing a camshaft, one size doesn’t fit all.