Racing Cam Basics - An Introduction To Camshafts

The racer today has a multitude of better camshaft options than they have had in the past. With some planning and forward thinking, you can develop a package that may work well at a number of different tracks. Changing rocker arms is much easier than changing camshafts to gain a power curve that better suits the track you are racing on at any given time. You can also play with valve lash to further tune the engine. These are all things you can discuss with your cam grinder when you are making your camshaft selections. The point is that you have options when you make cam selections. These options offer some variability on the component selections. It may not be the optimum, but you will be able to adjust, learn, and develop a better package on any given day.

For the racer who wants a camshaft that offers lower maintenance, the hydraulic camshafts offered today have the ability to produce some good power and offer a reliable lower maintenance package. Realize that low maintenance does not mean no maintenance. Even the OEM (Original Equipment Manufactures) offer hydraulic roller cams that can develop some very impressive power numbers in a product that was intended to last several hundred thousand miles. The hydraulic roller cams that are becoming standard equipment in many high output engines offer some real performance opportunities. These cams are being used to develop engines that are producing well over 500hp in cars that were intended to be driven on the street and have very good power delivery and torque characteristics.

Be aware, to get all the potential a cam can offer, all the components of the valvetrain need to be well matched. This is especially true of the valve springs. It is very easy to get a cam that will over-tax your valve springs or cause coil bind. It is also very important to check your valve springs for the necessary seat pressure and open pressure. This is a step that is often overlooked by the novice engine builder. If you do not have a valve spring checker, find someone who does and use it, or go to the local speed shop/engine builder and explain what you are doing and they may be willing to help you. It may cost a few dollars for them to check your springs, but it will be money well spent.

The real trick is that there is no trick at all. You need to ask questions, understand your application, ask some more questions, and define the work scope you will be requiring the engine to operate within. Selecting a camshaft is not brain surgery. And keep in mind that you have a variety of very knowledgeable cam vendors on the market today. They have a vested interest in just how well you do and how happy you are with their product.

The author can be reached at Vahok.Hill@cox.net.

These Terms Are Key To Understanding The Role Of The Camshaft

ABDC - After Bottom Dead Center is the point at which the piston is at is furthest point of travel at the bottom of the stroke (BDC). The piston is at the bottom of the cylinder bore. ABDC indicates the piston is now traveling up in the bore. This position is measured in degrees of crankshaft rotation.

Asymmetrical - This is a design feature on cam lobes. This is when the opening profile on the lobe is different from the closing lobe profile. The usual difference is to open the valve very quickly and then to close the valve at a much slower rate. This is done to make the mechanical forces acting on the valvetrain a little less severe. Easing the valve back on the seat is easier on the valvetrain than slamming the valve back on to the seat and causing the ensuing shock to the whole valvetrain. Conversely, on a symmetrical cam the opening and closing profiles on the cam are the same.

ATDC - After Top Dead Center, the piston has reached top dead center (TDC) and is now traveling back down the bore. This position is measured in crankshaft degrees.

Base Circle - The concentric or round portion of the cam lobe where the valve lash adjustments are made. If you were to remove the opening and closing ramps and the nose, the circle you would be left with is the base circle.

BBDC - Before Bottom Dead Center, the piston will be traveling towards the bottom of the stroke. This is measured in degrees of crankshaft rotation.