How-to Guides

How To: Camshaft Basics 101

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Engines destined to power modern cars and trucks have almost nothing in common with antique engines, except for one component: the camshaft. As you probably know, each cylinder in your engine has intake and exhaust valves to allow fresh air and fuel in, and then to evacuate the burned exhaust. The valves resemble the stem of a martini glass, with their circular bases sealing the top of each cylinder. Here is a close up of both valves which make up the top end of the engine.

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Each valve must open and close multiple times for each engine revolution, and the part that makes them open is called a cam. Cams have been around for decades, and they are basically a rod with one or more bumps, known as lobes, along its length. If you spin the rod, the lobes also spin and are used to open and close each valve.

Because cylinders fire in a specific order, each lobe on the cam is timed for a specific cylinder’s intake or exhaust valve. If you were to remove the cam covers on your car while the engine is running, you would see the heads of the valves being pummeled like a high speed whack-a-mole. You would also be sprayed with hot engine oil, so don’t do it.

Everything that happens inside your engine is dependent on the cam. It is the mechanical brain of the system. The shape and size of the lobes on the cam determine how fast and how long the valve will stay open, so if you change your cam it will make a major difference in how much air is allowed in and out of your engine. Your car will be much louder, even at idle.

(Source: © Interlink Media)
(Source: © Interlink Media)

Let’s look at the variables in selecting the best cam for your application. Most new cars have two or four cams, and the timing belts connecting them can be very complex. Multiple cams translates into more expensive parts and many more hours of work. Unless you have a complete set of tools for your car, a weekend off and friends to help you, swapping cams yourself can be a nightmare. For those unsure of their ability to undertake this endeavour, find a local shop specializing in your car and let them do it.

The main deciding factors in cam selection are lift and duration. Lift is how far the valve opens. Duration is how long the valve stays open, and this is measured in degrees of rotation. Higher lift allows more air in and out of the engine, but it brings the valve much closer to the piston. If they ever make contact you will need a new motor.

Think about your driving style. Do you want more torque at a lower rpm? Cams designed for bottom end power usually sacrifice top end performance. Conversely, if you want all your power on the upper end, your high rpm cam will make city driving very uncomfortable.  A midrange cam won’t confuse your computer and keep the pollution police at bay. Read every review you can, and ask owners what variables went into their selection process.

On the exhaust stroke of your engine, the piston moves upwards while the exhaust valve is open in order to force the exhaust downstream to the muffler. Once the exhaust valve closes, the intake valve opens to suck in fresh air and fuel, and the piston moves back down to fill the cylinder. Before the piston starts this intake stroke, the exhaust valve closes and the intake valve opens a split second later. If the intake and exhaust valves are open simultaneously, you have a condition known as overlap. Federal clean air laws mandate that overlap had to be eliminated because it allows unburned fuel down the exhaust. Overlap adds a ton of power as long as you have a free flowing exhaust to support it. If you know the durations of the intake & exhaust lobes, overlap can be calculated with tools online. Most cam companies publish their overlap to give customers a better idea of how radical it will be.

(Source: © Interlink Media)
(Source: © Interlink Media)

With the proliferation of computer numerical control (CNC) machines, many amateurs have tried to enter the market. A cheap cam might have very steep lobes that cause the valve to slam closed into its seat. If a valve slams shut too fast, it hammers the valve seat and sends destructive vibrations through the engine. Other amateurs try to “re-grind” or cut down the lobes of used cams to make them steeper and create more power. Regrinds are a prelude for disaster. Small timers don’t have the final machining abilities to harden and polish the steel, so stay away from any cams that have been reground. Do your research.

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Traditional cam manufacturers are still in business, and for a few hundred bucks they will custom grind anything you may need. They will ask for your goals, current and future upgrades, driving habits and even tire size in order to make the most power. A new cam will breathe new life into your car or truck. Take the road less traveled and find cams that match you or your car’s personality. Life is too short to drive a boring car.


(Photo credits: Source Interlink Media and Classic Industries)