A cam on a car refers to the camshaft, a rotating shaft inside your engine that controls when the intake and exhaust valves open and close. It’s one of the most critical components in any internal combustion engine because it determines how air and fuel enter the cylinders and how exhaust gases leave. Without it, your engine simply wouldn’t run.
What a Camshaft Actually Does
Your engine works by burning a mixture of air and fuel inside cylinders. For that process to happen efficiently, valves at the top of each cylinder need to open and close at precisely the right moments. The camshaft is the component responsible for that timing.
The camshaft is a long metal rod with egg-shaped lobes (called “cams”) machined along its length. As the shaft rotates, each lobe pushes against a valve or a valve lifter, forcing the valve open. When the lobe rotates past, a spring pushes the valve back closed. The shape, size, and position of each lobe determine exactly how far the valve opens, how long it stays open, and when it opens relative to the piston’s position in the cylinder. This entire sequence is called valve timing, and it has a huge impact on how much power your engine makes, how smoothly it idles, and how efficiently it burns fuel.
The camshaft is connected to the crankshaft (the shaft your pistons push on) by a timing chain, timing belt, or set of gears. This connection ensures the valves always open and close in sync with the pistons. In a four-stroke engine, the camshaft spins at exactly half the speed of the crankshaft.
OHV, OHC, and DOHC Explained
Where the camshaft sits inside the engine defines the engine’s basic design, and you’ll see these abbreviations on spec sheets and in car reviews.
- OHV (Overhead Valve): The camshaft sits inside the engine block, below the cylinder head. It operates the valves through a series of pushrods and rocker arms. This is an older, simpler design still used in many V8 truck engines. It’s compact and produces strong low-end torque, but the extra moving parts limit how fast the engine can rev.
- OHC or SOHC (Single Overhead Cam): The camshaft sits in the cylinder head, directly above the valves. This eliminates pushrods and allows the engine to rev higher and respond more quickly. Many four-cylinder and V6 engines use this layout.
- DOHC (Dual Overhead Cam): Two camshafts sit in each cylinder head, one for the intake valves and one for the exhaust valves. This gives engineers the most control over valve timing and is common in modern performance and fuel-efficient engines. A DOHC V6, for example, has four camshafts total (two per bank of cylinders).
How Cam Profiles Affect Performance
The shape of those egg-shaped lobes is everything. Engineers describe a cam’s characteristics using a few key measurements. “Lift” refers to how far the valve opens. “Duration” is how long (measured in degrees of crankshaft rotation) the valve stays open. Together, these define the cam’s profile.
A cam with higher lift and longer duration lets more air and fuel into the cylinder, which generally means more horsepower at higher RPMs. This is why aftermarket “performance cams” are a popular engine modification. The tradeoff is that aggressive cam profiles typically make the engine idle roughly and produce less power at low RPMs, which can make the car less pleasant to drive in stop-and-go traffic. Stock camshafts are designed to balance power, fuel economy, smooth idling, and emissions compliance.
You might also hear about “cam overlap,” which is the brief moment when both the intake and exhaust valves are open at the same time. More overlap improves high-RPM breathing but hurts low-speed efficiency. It’s one reason race engines sound lumpy at idle.
Variable Valve Timing
Modern engines don’t have to choose between a “mild” cam for everyday driving and an “aggressive” cam for performance. Most cars built in the last 15 to 20 years use some form of variable valve timing (VVT), a system that adjusts the camshaft’s position or the valve lift while the engine is running.
Toyota’s VVT-i, Honda’s VTEC, BMW’s VANOS, and Ford’s Ti-VCT are all brand-specific names for systems that do essentially the same thing: optimize valve timing across the full RPM range. At low speeds, the system behaves like a mild cam for smooth idling and good fuel economy. At higher speeds, it shifts to behave more like an aggressive cam for increased power. This is why modern four-cylinder engines can produce power numbers that would have required a V6 or V8 a generation ago, while still returning 30-plus miles per gallon on the highway.
Signs of Camshaft Problems
Camshafts are durable, but they can wear out or fail, especially if oil changes are neglected. The lobes ride against metal surfaces thousands of times per minute, and without proper lubrication, they wear down. A worn cam lobe won’t open its valve fully, reducing that cylinder’s performance.
Common symptoms of camshaft wear or failure include a ticking or tapping noise from the top of the engine, rough idling, misfires, a noticeable loss of power, and poor fuel economy. Your check engine light will usually come on, often with codes related to camshaft position sensor readings being out of expected range. In engines with variable valve timing, a failing cam phaser (the component that adjusts cam position) can produce a rattling noise at startup that fades as oil pressure builds.
Replacing a camshaft is a significant repair because the cylinder head typically needs to come off or at least be partially disassembled. Costs vary widely depending on the engine layout, but it’s generally a job that runs into four figures for parts and labor on most modern cars. Keeping up with oil changes using the correct oil weight is the single best thing you can do to protect your camshaft and its related components.
Aftermarket Cams and Modifications
Swapping the camshaft is one of the most effective single modifications for increasing an engine’s power output. In the world of V8 performance, a “cam swap” is often the first major modification enthusiasts make after bolt-on parts like intake and exhaust upgrades. A well-chosen aftermarket cam on a V8 can add 30 to 80 horsepower depending on the engine and supporting modifications.
The characteristic “loping” idle sound of a muscle car almost always comes from an aftermarket cam with high lift and long duration. That sound is the engine struggling slightly at low RPM because the aggressive valve timing is optimized for high-RPM power, not smooth idling. For many enthusiasts, that lumpy idle is half the appeal.
If you’re considering a cam swap, keep in mind that it usually requires recalibrating the engine’s computer (a “tune”) and may require upgraded valve springs to handle the increased lift without the valves “floating” at high RPM. On newer vehicles with variable valve timing, aftermarket cam options can be more limited and complex to install.