Camshaft Tech Guide

An engine’s camshaft is one of the most crucial parts of the engine. Without it, the rest of the engine would be rendered useless and unable to produce power, due to the fact that the air, fuel, and spark would not even reach it. The camshaft is such an important part of the engine, that merely changing how it operates can have a big impact on engine performance. Swapping the camshaft used to be a common upgrade in muscle cars, when more power was desired from the engine. In more recent years, even the car manufacturers have utilized the potential of the camshaft in power production. Technological advancements such as overhead camshafts and variable timing have made the Mustang camshaft operation much more important component than ever before.

There are three common types of camshaft configurations seen today, and the Mustang has seen all three of them used in its engines in the last couple of decades.

The Overhead Valve (OHV) configuration is becoming less common. In this configuration, the camshaft is placed in the engine block, and pushrods transfer the motion of the camshaft to rocker arms that open and close the valves in the head. The camshaft is in the engine block, below the valves, and the valves are in the engine head above the camshaft, hence the term, "Overhead Valve". As the camshaft rotates, lifters ride on the camshaft lobes, which raise the pushrods that rest on them. As the pushrods rise, they push one end of the rocker arm which, in turn, pushes the valve down and opens it.

Due to the number of components used in this type of camshaft approach, failure of the valvetrain can be a higher possibility than with the other options. While the quality of the components used will play a factor in this, the fact remains that using fewer components has a distinct advantage. In addition, the overhead valve configuration is the least efficient of the three types due to the friction and mass of all the components. The last overhead valve V8 Mustang was the 5.0, used up to 1995.

SOHC stands for Single Overhead Camshaft. It differs from the previous camshaft configuration by placing the camshaft at the top of the engine head. The camshaft is directly under the valve cover, and above the valves, giving it the Overhead Camshaft designation. The “Single” designation comes from the fact there is one camshaft mounted in each engine head.

The overhead configuration has a couple of distinct advantages. The first of these is the reduction of parts necessary for the camshaft to open and close the valves. The need for pushrods and lifters is eliminated, as the camshaft opens the valves by operating the rockers directly as it spins. This reduction of parts increases reliability, and makes the engine’s valvetrain much more efficient. The 4.6 Liter V8 found in the Mustang GT uses a Single Overhead Camshaft, in both the 2 Valve versions found from 1996 to 2004 as well as the 3 Valve versions found in the 2005 and later Mustang.

The Dual Overhead Camshaft (DOHC) is essentially the same configuration as the Single Overhead Camshaft, the difference being that there are two camshafts in each head, as opposed to one. For engines that use four valves per cylinder, Dual Overhead Camshafts are the preferred method of valvetrain operation, as the sheer number of valves it is necessary to operate really makes it a requirement. An example of this configuration is the 32 Valve engines used in the Mustang Cobra and Mustang Shelby GT500.

Camshaft timing refers to how the camshaft operates in relation to the crankshaft. This is referred to in degrees advanced or retarded, which essentially means before or after crankshaft rotation. Both the crankshaft and camshaft rotate a full 360°. Performance characteristics can be altered, however, by advancing or retarding the camshafts position relative to the crankshaft. This can be a complex procedure, and an incorrect setting can cause the engine’s pistons to strike the valves.

With fixed camshaft timing, the camshaft’s position is set when the camshaft is installed. While the overall engine timing can be altered, the camshaft’s relation to the crankshaft’s rotation will not change. This has a distinct disadvantage, in that the camshaft’s profile is going to be optimized for a somewhat narrow RPM range.

With variable camshaft timing, you will still have the positioning set when the camshaft is installed. As the engine’s RPM changes, however, the camshaft’s rotation in relation to the crankshaft can change. This makes the camshaft’s profile effective at a much greater RPM range, as the camshaft’s timing can advance and retard as needed. In the 2005 and later Mustangs, variable camshaft timing is controlled by oil pressure in conjunction with oil control solenoids and camshaft phasers. Due to the wide variation in camshaft timing allowed by the factory setup, some aftermarket camshafts require the variable timing to be limited, or eliminated altogether.

When looking at a camshaft, there are some terms that are often thrown around, and defining these terms may prove useful when shopping for a camshaft. Although basic understanding of these aspects help to tell you how the camshaft will operate, it’s always a good idea to consult the manufacturer or speed shop to get assistance in determining the best camshaft for your particular application.

• Centerline: Where the lobe hits its peak lift, after opening the valve.
• Duration: The degrees the valve is held open.
• Lift: How far the lobe opens the valve
• Lobe Separation Angle: The degrees between the centerline of the exhaust and intake lobes.
• Overlap: The degrees that both the intake and exhaust valves are open.

While a comprehensive breakdown of camshaft variables and theory would take hours, one factor is very important for those going down a forced induction path. That is: exhaust duration. Since forced induction is one of the most popular and best ways to get power from an engine, we’ll cover it briefly. Keep in mind, however, that even a naturally aspirated motor can benefit from a proper camshaft swap.

Whether you are supercharging or using nitrous, you are forcing air into the engine and the intake duration becomes much less important than the exhaust. The exhaust overlap is crucial, however, as you still need to get the larger-than-normal amount of spent gas out of the combustion chamber and out of the cylinder. The longer overlap means that the intake and exhaust valves are open together longer, which increases the scavenging of fresh air into the cylinder. This scavenging pushes the spent gases out better than a camshaft with a shorter exhaust overlap. This is the reason you’ll often see camshaft manufacturers offer blower or nitrous cams.

If you’re exploring the potential of a camshaft, examine your options carefully, and definitely make use of the manufacturers and retailers knowledge. Most of the time, they’ll know their camshaft lines much better than you will. There are plenty of options available, and some present a more complicated install than others. They can also help you determine whether the install is possible to do yourself, or whether you’ll want to have someone do it for you. Regardless, the proper camshaft for your application can ultimately reward you with some very noticeable extra horsepower.