What Do Camshafts Control?

Camshafts control the opening, closing, lift, and duration of intake and exhaust valves in an internal combustion engine, thereby governing airflow, combustion efficiency, power delivery, fuel economy, and emissions. In modern engines, variable systems allow the camshaft’s effect to change with speed and load for better performance and efficiency.

The core function: managing valve events

At the heart of a four-stroke engine, camshafts convert rotational motion into precisely timed linear motion that operates the valves. Each cam lobe’s shape determines how quickly a valve opens, how far it lifts, how long it stays open, and when it closes relative to crankshaft position. By synchronizing these events via a belt, chain, or gears, the camshaft controls how effectively the engine breathes across the rev range.

How it works mechanically

The camshaft’s lobes press on lifters (tappets), pushrods, and rocker arms—or act directly on the valves in overhead-cam designs—to open valves against spring pressure. The valve springs then close the valves as the lobes rotate away. The camshaft is timed to the crankshaft so that valves open and close at the correct points in the intake, compression, power, and exhaust strokes.

SOHC, DOHC, and cam-in-block layouts

Engines may use a single overhead camshaft (SOHC) to operate both intake and exhaust valves, dual overhead camshafts (DOHC) with separate cams for intake and exhaust for finer control, or a cam-in-block (pushrod) design where a single camshaft in the engine block operates valves through lifters and pushrods. These layouts influence how precisely valve events can be tuned and how high an engine can safely rev.

What camshafts directly control

The following points summarize the specific aspects of valve operation and engine behavior that camshafts control through lobe shape and timing.

• Valve timing: the crankshaft angles at which intake and exhaust valves begin to open and finish closing.
• Valve duration: how long (in crankshaft degrees) each valve remains open.
• Valve lift: how far a valve opens, affecting peak airflow into and out of the cylinder.
• Valve overlap: the period when intake and exhaust valves are open together, aiding scavenging and influencing emissions and idle quality.
• Breathing characteristics: the volumetric efficiency curve that shapes torque at low rpm and power at high rpm.
• Combustion quality and efficiency: by controlling the fresh charge and residual gases, camshafts influence knock resistance, fuel economy, and emissions.

Together, these variables determine an engine’s character—whether it idles smoothly and sips fuel or surges at high rpm with maximum output. Changing cam profiles or phasing shifts these trade-offs.

Modern control technologies on camshafts

Contemporary engines enhance or vary camshaft effects dynamically to widen the usable powerband and improve efficiency and emissions under real-world driving.

• Variable valve timing (VVT): hydraulic or electric cam phasers advance or retard cam timing relative to the crank, optimizing torque, power, and emissions across different speeds and loads.
• Variable valve lift/duration: mechanisms (e.g., Honda VTEC, BMW Valvetronic, Fiat MultiAir) alter lift and/or duration, improving part‑load efficiency and high‑rpm breathing.
• Dual independent cam phasing (on DOHC engines): allows separate intake and exhaust cam adjustments, fine‑tuning overlap for better scavenging and catalytic converter performance.
• Cylinder deactivation lifters: on some cam-in-block engines, special lifters collapse to keep selected valves closed, reducing pumping losses under light load.
• Camless/actuator-driven systems (emerging): replace cams with electro-hydraulic or electromagnetic actuators for fully flexible valve control; still rare in mass-market cars.

These technologies let one engine behave like many—efficient at cruise, responsive in the midrange, and powerful at higher rpm—without sacrificing drivability or emissions compliance.

What camshafts do not primarily control

While central to valve operation, camshafts do not directly set ignition timing or fuel injection timing in modern engines; those are handled by electronic control units using sensors (including cam and crank position sensors). In some designs, the camshaft mechanically drives ancillary components (e.g., a mechanical fuel pump, distributor on older engines, or a vacuum pump), but its primary control remains the valve events.

Context beyond four-strokes

Most two-stroke gasoline engines use ports in the cylinder walls rather than camshafts for gas exchange. However, many large two-stroke and four-stroke diesel engines still use camshafts to operate valves and, in some cases, to actuate unit injectors. Regardless of application, the camshaft’s essential role is timing motion precisely.

Summary

Camshafts control when and how far intake and exhaust valves open and close, determining airflow, overlap, and the engine’s torque, power, efficiency, and emissions. With modern variable systems, camshafts can adjust their influence on the fly, delivering broader performance and cleaner operation while retaining their fundamental role as the engine’s valve-timing orchestrator.

What happens when a camshaft goes bad?

When a camshaft goes bad, you might notice symptoms like a rough idle, engine misfires, lack of power, a lit check engine light, a loud ticking or tapping noise from the engine, increased fuel consumption, and difficulty starting the vehicle. These issues arise because a faulty camshaft fails to correctly open and close the engine’s intake and exhaust valves, disrupting the engine’s combustion and timing. 
This video explains the common symptoms of a bad camshaft, including engine misfires and noises: 53sKamsiparts Automotive YouTube · Sep 14, 2023
Common Symptoms of a Bad Camshaft

• Rough Idle and Misfires: The camshaft’s timing is crucial for proper combustion. A worn or damaged camshaft can lead to inconsistent valve operation, causing the engine to run roughly and misfire. 
• Engine Performance Issues: You may experience a noticeable loss of power, hesitation during acceleration, and a general lack of responsiveness from the engine. 
• Check Engine Light: A malfunctioning camshaft can trigger sensors, causing the “Check Engine” light to illuminate on your dashboard. 
• Abnormal Noises: A worn camshaft or damaged camshaft bearings can create loud tapping or ticking sounds, especially from the upper part of the engine. 
• Increased Fuel Consumption: Inefficient combustion due to poor valve timing can lead to a drop in your vehicle’s fuel efficiency. 
• Stalling and Starting Problems: Severe camshaft issues can disrupt the engine’s operation, leading to stalling, particularly at low speeds, or difficulty getting the engine to start. 
• Backfiring: Incorrect valve timing can allow unburnt fuel to ignite outside the combustion chamber, resulting in loud pops or bangs from the exhaust or intake. 
• Metal Shavings in Oil: As the camshaft lobes wear down, they can shed metal particles into the engine oil, which can be seen when draining the oil. 

Why It Matters
A bad camshaft is a serious issue that can lead to extensive and expensive engine damage if not addressed promptly. Early replacement can help restore engine performance, improve fuel efficiency, and prevent further harm to related engine components. 
This video explains the importance of a camshaft position sensor and how it relates to engine timing: 57sCar Care CluesYouTube · Nov 6, 2024

What does the camshaft control?

A camshaft controls the precise timing of a vehicle’s engine valves, ensuring they open and close at the exact moments needed for the engine’s four-stroke cycle to occur. It regulates how much the valves open (lift), how long they stay open (duration), and when they open and close, allowing the engine to intake fuel and air and expel exhaust. This critical function enables the engine to run efficiently and smoothly.
 
How the Camshaft Works

• Driven by the Crankshaft: The camshaft is connected to the crankshaft via a timing belt or chain. 
• Asymmetrical Lobes: The camshaft has asymmetrical lobes, or bumps, that are precisely shaped. 
• Valve Actuation: As the camshaft rotates, these lobes push against other engine components, such as rocker arms or lifters, which in turn open and close the engine’s intake and exhaust valves. 

Why It’s Important

• Engine Breathing: Opens in new tabThe camshaft allows the engine to “breathe” by controlling the flow of the air-fuel mixture into the combustion chamber (intake) and the expulsion of burned gases (exhaust). 
• Engine Performance: Opens in new tabBy controlling the timing and amount of valve lift and duration, the camshaft directly influences the engine’s power output, fuel efficiency, and overall smoothness. 
• Engine Damage Prevention: Opens in new tabThe camshaft’s timing is synchronized with the pistons’ movement; if a timing belt breaks, the pistons can strike the valves, causing severe engine damage. 

What are the four main functions of a camshaft?

Advantages of Camshafts

• Precisely controls valve timing for optimal engine performance.
• Enhances fuel efficiency and power output.
• Enables smooth and efficient intake and exhaust processes.
• Supports variable valve timing for improved engine flexibility.

Does a camshaft increase horsepower?

Yes, a performance camshaft can increase horsepower by optimizing airflow into and out of the engine’s cylinders, usually by increasing valve lift or duration to allow more air and fuel to enter the combustion chamber. However, this increase in high-RPM power often comes at the cost of lower-end torque and potentially a rougher idle, so the choice of camshaft should align with the specific needs and intended use of the engine. 
How a Camshaft Increases Horsepower

• Increased Airflow: A performance camshaft is designed with lobes that are “bigger or longer” than stock, which increases valve lift (how far the valves open). This allows a greater volume of the air-fuel mixture to enter the cylinders, leading to more power. 
• Increased Duration: The camshaft also controls valve timing, or duration, which is the amount of time the valves remain open. Longer duration allows more time for the engine to “breathe” and fill the cylinders, boosting high-end power, notes Quora. 
• Engine Breathing: By changing the valve lift and duration, a performance camshaft directly affects how the engine “breathes,” improving the flow of air and exhaust. 

Considerations and Trade-offs

• Power Band: Opens in new tabThere’s a trade-off between low-RPM torque and high-RPM horsepower. A cam optimized for peak horsepower will likely sacrifice some low-end performance. 
• Engine Characteristics: Opens in new tabThe stock camshaft is a compromise designed for a specific balance of performance and drivability. An aftermarket cam changes this balance to suit different goals. 
• Other Modifications: Opens in new tabA camshaft upgrade often works best in conjunction with other engine modifications, such as improved exhaust and intake systems, to fully realize its potential.