Choosing The Right Camshaft: A Comp Cam Selection Guide | JEGS (2024)

Choosing a camshaft is one of the most important decisions to make when building or upgrading your engine. The camshaft is often referred to as the "heart" of an engine, determining how far and how long the valves are open. Many other components such as cylinder heads, valve springs, and the torque converter are selected based on the camshaft specifications. Careful research and planning around the camshaft will produce the best engine performance. Before purchasing a camshaft, it is important to understand how it works and how changes in its design affects performance. Below are terms and explanations that will help you in your search for the best camshaft.

Camshaft Lift

It's important to be aware of a few ways camshaft lift is talked about. Cam lobe lift, also called Gross Lift, is the distance a cam moves a lifter/tappet. Because a rocker arm multiplies the movement of the tappet, valve lift is not the same as cam lobe lift. For example: A cam with a lobe lift of .4 inches will move a valve .6 inches with a 1.5:1 rocker arm ratio (1.5 x .4). A different ratio rocker arm will change the valve lift, but not the lobe lift of a cam. You can therefore increase valve lift by using an increased rocker arm ratio. More cam lift means the valve will open further. Increasing cam lift will allow more air or exhaust to move through an engine. If you plan on upgrading your cam to increase lift, you must be sure your valve springs are capable of handling a cam with increased lift. Piston to valve clearance can also become an issue. Verify that you will have enough clearance before you buy a new cam.

Camshaft Duration

Camshaft Duration is the measurement of the time one valve begins to open until it finishes closing. Duration is measured in degrees of crankshaft rotation, not camshaft rotation. You'll see duration specifications at .050 inches. Cam manufacturers agreed on a standard to measure duration so all cams are measured the same way. The idea is to measure duration starting at .050 inches of tappet (lifter) movement. As the lobe lifts the tappet up, when the tappet moves .050 inches, the duration is measured from that point.

Intake Duration at .050 inch Lift - The number of degrees the crankshaft moves while the intake valve is open. Cam manufacturers agreed to measure and give camshaft duration based on the lifter moving .050 inches. This made duration numbers easier to compare between different cam manufacturers.

Exhaust Duration at .050 inch Lift - The number of degrees the crankshaft moves while the exhaust valve is open. Cam manufacturers agreed to measure and give camshaft duration based on the lifter moving .050 inches. This made duration numbers easier to compare between the different cam manufacturers.

Camshaft Lobe Separation (In Degrees)

Camshaft lobes on standard V8's, like the small block Chevy, are arranged in pairs: One intake lobe, one exhaust lobe. Those pairs of lobes are phased to each other. Cam lobe separation is the angle in degrees between maximum lift of a pair of cam lobes. To picture cam lobe separation a little better, look at the end of a traditional V8 camshaft. Draw a line through the center of the cam out through the point of maximum lift on each cam lobe on a pair of lobes. You'll usually find the measurement between 104 and 115 degrees. It's important to note that Lobe Separation describes how the intake valve reacts in relation to the exhaust valve in the same cylinder. Where cam lift and duration describe the effect of each lobe on a valve. Cam Lobe Separation is an important performance characteristic because it times the intake and exhaust valves. If the Lobe Separation angle was 0 degrees, both intake and exhaust valves would be opened and closed at the same time. That obviously won't work, but it may help us understand what happens as the separation angle decreases or increases on a cam.

If the Lobe Separation Angle is narrower: As a cam turns, one valve opens. As the cam continues to turn, that valve starts to close. Since the angle is narrower, the 2nd valve in the pair is beginning to open before the first one is closed. How far the first valve is open when the 2nd valve begins to open depends on the Cam Lobe Separation. (The shape of the cam lobe also affects this.) A narrow angle will increase cylinder pressure, make an engine idle worse and reduce idle vacuum. Cylinder pressure increases because after the exhaust stroke, the piston is pulling air into the cylinder. If the intake valve opens earlier, more air can be sucked into the cylinder.

If the Lobe Separation is Wider: As a cam turns, one valve opens. As the cam continues to turn, that valve starts to close. With a wider angle, the 2nd valve in the pair is starting to open later. With the right angle, you could time the first valve to be closed before the second one opens. With a wider separation angle, cylinder pressure is reduced, idle is smoother and idle vacuum is better.

Which Camshaft is best for me?

If you have read this whole article, by now your head might be spinning and rightfully so. Camshafts are very complex mechanisms that entail a myriad of numbers, and there are literally millions of grinds out there. Luckily, most camshaft manufacturers have made it a much easier for the hobbyist to select a camshaft than ever before.
Cam Rule #1: If you are having your engine assembled by a professional engine builder, involve their opinions and knowledge in the selection. Nothing beats experience.
Cam Rule #2: The most common mistake in a cam selection is to select a cam that is too big, thus hurting performance. If you are deciding between two camshafts, typically the smaller grind is the wise choice.
If your knowledge is limited and you are set on selecting a cam yourself, pay the closest attention to two elements that are advertised by all camshaft manufacturers. First is the RPM band. This RPM or power band will denote the efficiency range that the camshaft was designed for and is typically displayed as "1500-6500RPM" for example. Match this RPM band closely with the intended use of the engine. Street cars will tend to spend more time at low RPM than High RPM, so an idle-5,500 or 1,500-6,500 would be best. Likewise, a high RPM race car that spends most of its time in the upper ranges will typically like cams that state 2,500-7,000 RPM or 3,500-8,000 RPM as two examples. The second element is the description or characteristics explanation of the camshaft. Most cam manufacturers put together a two or three sentence description of what the camshaft is best used for and/or it performance characteristics. These descriptions are like cliff notes for cam selection instead of having to read and understand the whole novel. Pick the one that describes best what you want and your intentions for the engine and you will typically make a wise choice. At JEGS we offer excellent Camshaft Manufactures such as Comp Cams, Crane Cams, Edelbrock, Ford Racing, Chevrolet Performance, Mopar Performance, Lunati, Crower, and Speed Pro. We also have our own JEGS line of Camshafts that we are proud of as well. If you would like to contact us for our advice feel free to call our tech line. Do not hesitate to utilize our JEGS Ask A Tech option and submit your questions to one of our experienced team members who will be excited to help you with any of your High Performance needs.

Frequently Ask Questions About Camshafts

The camshaft is the "heartbeat" of the engine. It controls the valve opening and all engine parts ideally should match it to maximize engine performance. There are many options available when selecting a camshaft. Below are the answers to the most common questions about camshafts:

What Do Camshafts Do?

An engine camshaft controls the opening and closing of the intake and exhaust valves. It is driven by the crankshaft through a timing set. It controls the valves by moving the lifters and push rods vertically into the underside of the rocker arms, which pivot and then push down on the valves. The lobes on the camshaft are ramped to allow smooth transition of vertical up and down movement as the camshaft rotates. The height of the lobes produces the "lift", which is how far the valves open. The amount of time the camshaft holds the valve open is the "duration". The longer the valves are open, the more air and fuel that can enter and exit the engine. Longer duration improves top end power at the cost of low-end torque and vice versa. Lobe separation angle is the amount of time that both the intake and exhaust valve are open at the same time in a cylinder. The lower the lobe separation angle, the rougher the idle and the more midrange power it will have. There are different types of camshafts to choose from when choosing the correct camshaft. The first choice is the lifter type: hydraulic or a mechanical lifter version. They hydraulic is best for daily drivers and vehicles putting a lot of time and miles on the engine as lash adjustment is not needed periodically. A solid (or mechanical) lifter is best for applications over 6500 rpms and produces more horsepower than a hydraulic lifter, but requires frequent valve lash adjustments. The choice for camshafts also involves the lifters: flat-tappet and roller. Flat tappets have a flat bottom on the lifter that contacts the camshaft lobe as the cam rotates. Roller lifters have a roller wheel that contacts the camshaft lobe, providing more power than flat tappet lifters due to the large decrease in friction. However, the cost is a lot more due to the bearings and rollers required for assembly of the lifter. An important rule to follow is that lifters have to match the types of camshafts they are designed for. A solid flat tappet cam is only compatible with solid flat tappet lifters; a hydraulic roller camshaft only works with hydraulic roller lifters. If you need help picking the right camshaft, a JEGS expert is ready to answer your questions and help you with how to choose a camshaft that you require for your specific application.

What Are Camshafts Made Of?

Most camshafts are made from either cast iron or billet steel. Billet steel is stronger than cast iron and is ideal when using stiffer valve springs and with high horsepower engines due to the increased strength and wear resistance. However, they are more expensive than their cast iron counter parts. JEGS offers a large selection of camshafts to choose from that will meet your needs.

How to Install Camshafts

Installation of a camshaft can be an easy process with the proper planning and tools. To install the cam, the engine short block needs to be complete with the crankshaft installed so that the timing set can be added. If you are replacing a camshaft, the old camshaft, lifters, and pushrods need to be removed. The camshaft bearings need to then be inspected for wear or damage and replaced if necessary (or added if using a new block). The new camshaft needs lubricated with camshaft assembly lube. Installation of a cam can be helped with a camshaft installation tool, which aids in holding it straight as it is carefully installed into the block. Care must be taken to ensure the cam does not damage the bearings as it passes through the block during installation. Once installed, the timing set needs to be added, making sure that the camshaft and crankshaft are properly clocked. Once the timing set is installed, the lifters and pushrods can be added. Next, adjust the rocker arms to the proper valve lash, depending on the type of camshaft and according to the proper order and procedure. Finally, degree the cam. This is important to prevent piston to valve contact, confirm correct assembly, and to provide maximum performance.

Can't Find The Camshaft You Are Looking For?

A JEGS expert is ready to answer your questions and help you find the camshaft that you require for your specific application.