Racing Cam Basics - An Introduction To Camshafts

It seems like no other part of the modern racing engine elicits as many questions or as much mystery as the camshaft.

From a physical perspective, the camshaft is a fairly simple part. There are millions, maybe billions, of them operating in internal combustion engines the world over. Every four stroke gasoline and diesel engine has at least one camshaft.

In the racing world we have many choices. The selection process can be as simple as selecting a camshaft from a catalog and installing it in the engine. Or it can be as complex as working with a cam grinder to develop custom profiles that you think will best suit your application. Or you can take the time to match all of the components that make up the valvetrain so you can optimize the potential of the cam and the power it can generate.

In a direct comparison, it is easy to see how the LS series camshaft has a much larger base circle than the conventional small block Chevrolet. The LS type cam is on the bottom. The larger core offers several benefits. The larger base circle means the cam is stiffer than the conventional small block cam and offers some other design and strength options that were previously only available on specialty aftermarket racing blocks or specially machined OEM blocks.

I favor the latter of those options. The differentiator is the amount of resources-i.e. the time and money-that you are willing to apply to this engine part. Done correctly, you need to integrate the camshaft design to match the other components of the engine to match the intended use of the engine.

From a simplistic perspective, the camshaft is responsible for opening and closing the intake and exhaust valves through the valvetrain. The cam actuates the lifter which actuates the pushrod which actuates the rocker arm which pushes the valve open. The valve springs are responsible not only to close the valve as the camshaft travels from full lift to the full closed position, but they help control the whole system by keeping tension on the valvetrain. In the overhead valve engines we use in circle track racing today, this is a pretty concise description. There are some differences depending on whether you have an overhead cam engine-specifically, some parts of the valvetrain will be different-but in principle the function is the same: The cam is responsible for opening and closing the valves.

It is clear that to fully understand the operation of the cam within the parameters of the engine, we need some common vocabulary. The cam and valvetrain have some very specific terminology that is critical to any meaningful dialog about camshafts.

Beginning The Process

We need to understand how to select a cam that will suit our needs. First, we need to ask some questions.

This roller lifter looks like it has seen some service. It has been in use for three seasons in a circle track application. Good maintenance habits have prevented any premature wear or failure. Performance does not have to cost a fortune.

- Are the rules in my racing association specific about cam types?
* Are roller cams legal?
* Do I have to use a hydraulic cam?
* Are there any rules even governing camshafts?

The point here is you need to ask some questions and read the rules that govern the class you are planning to race in.

What are the other engine parameters that we have to work with? Does it make a difference?

After talking with David McCarver at Comp Cams, the more specifics you can define the easier it will be to make a cam selection to suit your needs.

"You need to integrate the cam into the whole engine package-displacement, compression ratio, heads, intake manifold, headers and fuel system, carburetor or fuel injection," says McCarver. "You also need to project the kinds of rpm levels that will be the peak and the average. Once you have all that data, you need to talk about the type of track or tracks you will be racing. Dirt or asphalt is just the first level of discrimination you need to define. Are the corners tight and the straights short, or is the track banked with very fast corners and long straights?"

These characteristics of the track will, according to McCarver, affect the decisions you make about the camshaft that you select.

"The biggest mistake that racers make is that they tend to want to put more cam in the engine than it needs or can handle," he says.

This cutaway LS series Chevrolet engine shows how the cam is driven off of the crankshaft by a single row chain and sprocket. But it's not the usual high performance dual row chain setup we are used to seeing in small block Chevrolets, Fords and Dodges.

This is a high-lift long-duration roller cam as evidenced by steep ramps and the wide nose on the lobe. This cam is destined for high horsepower applications.

This is a Jesel belt-drive cam drive. This option has some advantages over a chain. The biggest advantage is the ability to advance or retard the camshaft with a minimum of teardown required. The drive is isolated from engine oil and the cover is easily disassembled to allow access to the cam sprocket, allowing the tuner to adjust the cam.