What a Camshaft Does: How It Times an Engine’s Breath

A camshaft opens and closes an engine’s intake and exhaust valves in precisely timed sequences, controlling how air-fuel mixture enters and exhaust leaves the cylinders. By rotating (typically at half the crankshaft speed in a four-stroke engine), its egg-shaped lobes push on lifters, rockers, or followers to actuate valves, setting the engine’s breathing, power delivery, efficiency, emissions, and idle quality.

Core Function and Timing

In a four-stroke engine—intake, compression, power, exhaust—the camshaft synchronizes valve events with piston position. The lobe’s shape and orientation dictate when a valve begins to open, how far it lifts, how long it stays open, and when it closes.

The camshaft is mechanically linked to the crankshaft by a belt, chain, or gears. On most gasoline and many diesel engines, it turns at one-half the crankshaft speed so each cylinder sees one intake and one exhaust event per two crank revolutions. In heavy-duty diesels and older mechanical diesels, the camshaft can also drive fuel injection events via cam-actuated injectors.

Why It Matters

The camshaft’s profile and timing have wide-ranging effects on how an engine behaves in real-world driving. The points below highlight the key outcomes that flow from cam design.

• Power curve: Aggressive profiles can boost high-rpm horsepower; milder profiles favor low-end torque and drivability.
• Efficiency and emissions: Correct timing reduces pumping losses and unburned hydrocarbons, improving fuel economy and tailpipe cleanliness.
• Idle quality and noise: Overlap-heavy cams can cause loping idle; refined cams smooth idle and reduce valvetrain noise.
• Reliability and durability: Materials, lubrication, and follower type (roller vs. flat tappet) influence wear and longevity.

Tuning the camshaft—alone or with software and intake/exhaust changes—lets engineers and builders tailor engines for daily driving, towing, or racing.

Design Types and Locations

Overhead Cam (OHC: SOHC and DOHC)

Single Overhead Cam (SOHC) and Dual Overhead Cam (DOHC) layouts place the camshafts in the cylinder head above the valves. SOHC typically uses one cam per bank to operate both intake and exhaust valves; DOHC uses two, allowing finer control and often four valves per cylinder for better breathing.

Cam-in-Block (OHV/Pushrod)

Overhead Valve (OHV) designs mount the camshaft in the engine block. Pushrods and rocker arms transmit motion to the valves. This design keeps engines compact and torquey, common in many American V8s, though valve control at high rpm can be more challenging.

Two-Stroke and Exceptions

Most two-stroke engines do not use camshafts; they time intake and exhaust using ports in the cylinder wall uncovered by piston movement. Some specialty engines and motorcycles use desmodromic systems (e.g., Ducati) that mechanically open and close valves to avoid spring-related valve float.

Variable Valve Timing and Lift

Modern engines optimize valve events across a wide rpm range using variable systems. These adjust when valves open (phasing) and how far/long they open (lift and duration) to balance torque, efficiency, and emissions.

• Cam phasing: Rotates the camshaft relative to the crank (e.g., VVT, VCT, VANOS), advancing or retarding timing to suit load and speed.
• Variable lift/duration: Alters lobe effect on the fly (e.g., VTEC, i-VTEC, Valvetronic, MultiAir) for low-rpm efficiency and high-rpm power.
• Cylinder deactivation: Closes valves on select cylinders under light load to reduce pumping losses and fuel use.
• Dual independent control: Separately phases intake and exhaust cams for finer control of overlap and exhaust gas recirculation.

These technologies let a single engine behave like multiple engines: smooth and frugal at low speed, strong and responsive at high speed.

Camshaft Geometry and Performance Terms

Several specifications define how a cam behaves. Understanding these helps explain tuning choices and their trade-offs.

• Lift: Maximum valve opening height; more lift usually increases airflow but stresses springs and followers.
• Duration: Crankshaft degrees a valve stays open; longer duration favors high-rpm power but can hurt idle and low-end torque.
• Lobe Separation Angle (LSA): Angle between intake and exhaust lobe centers; tighter LSA increases overlap and responsiveness but roughens idle.
• Overlap: Period when intake and exhaust valves are open together; helps scavenging at high rpm but can dilute mixture at idle.
• Ramp rate: How quickly lift changes; steeper ramps improve flow yet risk wear and valve train noise if not engineered carefully.

Cam specs are a balancing act: small changes can shift the engine’s character, so choices depend on intended use and supporting hardware.

Drive, Materials, and Lubrication

Camshafts are driven by timing belts (quiet, periodic replacement), chains (durable, tensioner-dependent), or gears (robust, used in racing/heavy-duty). They are typically made from chilled cast iron or billet steel. Roller followers reduce friction and wear; flat-tappet designs require strict break-in and zinc-rich oil. Adequate lubrication is vital, as lobes and followers experience high contact stresses.

Sensors and Engine Control

A camshaft position sensor reports cam phase to the engine control unit, enabling sequential fuel injection, coil-on-plug ignition timing, and closed-loop control of variable valve timing. Working alongside the crankshaft sensor, it ensures accurate start-up, smooth idle, and compliance with emissions diagnostics.

Maintenance and Common Issues

Keeping the camshaft and its drive healthy prevents costly failures and performance loss. The following points outline what owners and technicians watch for.

• Timing belt intervals: Replace belts, tensioners, and water pumps as specified to avoid catastrophic valve-to-piston contact.
• Chain stretch and guide wear: Causes timing drift, noise, and check-engine lights; timely service averts larger damage.
• Lobe/follower wear: More common on flat-tappet setups or with poor lubrication; shows as misfires, ticking, or power loss.
• Valve lash/clearance: Periodic adjustment on mechanical lifters prevents burnt valves and noise; hydraulic lifters self-adjust but can fail.
• Cam sensor faults: Trigger hard starts, rough running, and diagnostic trouble codes; often fixed with sensor replacement or wiring repair.

Recognizing early signs—rattles on cold start, rough idle, or reduced performance—can save an engine from major repairs.

The Future: Toward Camless?

Electrohydraulic and electromagnetic systems aim to remove camshafts entirely, giving per-valve, per-cycle control (e.g., Koenigsegg’s Freevalve concept). While promising for efficiency and flexibility, these systems are rare in mass-market cars due to cost, complexity, and durability hurdles. Hybrid powertrains and advanced variable systems continue to narrow the gap meanwhile.

Summary

The camshaft choreographs valve motion in sync with the pistons, governing how an engine breathes. Its design, drive system, and control strategies shape power, efficiency, emissions, and reliability. From classic pushrods to sophisticated variable timing and lift, cam technology remains central to how internal combustion engines perform today—and a key area of innovation for tomorrow.

What happens when the camshaft goes bad?

A faulty camshaft can cause misfires by disrupting the timing of the valves. If the camshaft lobes are worn or damaged, they may not open the valves correctly, leading to incomplete combustion in the cylinders. This improper combustion results in misfires and can cause further damage to your engine.

Do camshafts increase horsepower?

Now an aftermarket cam shaft manipulates lift and duration. Which subsequently manipulates how much air and fuel is being drawn into the combustion. Chamber more air obviously equals more horsepower.

Is it worth replacing a camshaft?

• Increased Power: Upgrading camshafts can improve the engine’s power output by allowing for more air and fuel to enter the combustion chamber.
• Tuning: If you’re looking to optimize your engine for specific RPM ranges, upgraded camshafts can enhance performance in those areas.

What is the purpose of a camshaft?

Camshafts are integral components of internal combustion engines, responsible for controlling the opening and closing of the engine’s intake and exhaust valves. As the camshaft rotates, its lobes push against the valves, allowing the intake of air and fuel and the expulsion of exhaust gases.