How a Cammed Engine Works

A “cammed” engine is one fitted with a performance camshaft that opens the intake and exhaust valves farther and for longer than stock, shifting torque higher in the rev range and often producing a choppy, lopey idle due to increased valve overlap and reduced vacuum. In practice, the camshaft’s shape and timing dictate how the engine breathes—more aggressive profiles improve high‑rpm airflow and power but can compromise idle quality, drivability, fuel economy, and emissions unless the rest of the combination and tuning are matched.

What “Cammed” Really Means

Enthusiasts use “cammed” to describe engines with aftermarket or reprofiled camshafts. While every four-stroke engine already has a camshaft (or cam profiles in an overhead-cam design), the term implies a cam with more lift and duration than the factory piece, and often a tighter lobe separation angle, to increase cylinder filling at higher rpm.

The Camshaft’s Job in a Four-Stroke Engine

The camshaft controls valve events that coordinate with the piston’s position through the four-stroke cycle. Below is a simplified sequence of how those events influence combustion and power.

1. Intake stroke: The intake valve opens before the piston reaches top dead center (TDC) to start airflow early; a bigger cam opens it farther and keeps it open longer to pack more air-fuel mix in at higher rpm.
2. Compression stroke: Both valves close and the mixture is compressed; long duration can delay intake closing, reducing low‑rpm dynamic compression but benefitting high‑rpm flow.
3. Power stroke: Both valves remain closed during combustion; cam profile here matters less directly but influences trapping efficiency set up by prior events.
4. Exhaust stroke: The exhaust valve opens before bottom dead center (BDC) to release pressure; near TDC, overlap occurs when both valves are slightly open to help scavenge exhaust and draw in fresh charge at speed.

This sequence shows why aggressive timing increases high‑rpm breathing yet can soften low‑rpm response: the same valve events that aid flow at speed can leak mixture or reduce effective compression at idle.

The Three Big Cam Specs That Change Behavior

Cam cards list several dimensions; the following are the most influential for how a “cammed” engine feels and sounds.

• Lift: Maximum valve opening. Higher lift exposes more curtain area for flow, often adding power across the band if the heads can use it, but requires stronger springs and adequate piston-to-valve clearance.
• Duration: How long (in crank degrees) a valve stays open. Longer duration shifts the powerband up, typically hurting idle vacuum and low‑rpm torque while improving top‑end power.
• Lobe Separation Angle (LSA) and Centerlines: The angle between intake and exhaust lobes; tighter LSA (e.g., 106–110°) increases overlap and lope, while wider LSA (112–116°) smooths idle and broadens torque.

Tuning these variables is a balancing act: more lift and duration can make more power, but only when matched to the cylinder heads, compression ratio, intended rpm, and vehicle use.

Why a Cammed Engine LOPES

The distinctive “lope” or choppy idle comes from valve overlap combined with low exhaust and intake flow velocity at idle. This causes exhaust reversion into the intake and unstable combustion, which the ECU or carb compensates for with extra fuel and timing, producing the rhythmic surge.

Modern Twist: Variable Valve Timing (VVT)

Many 2000s–2020s engines use cam phasers to advance/retard cam timing on the fly. This widens the usable powerband and calms idle with milder cams, or it can help tame moderate aftermarket profiles. However, very aggressive cams may require limiting or deleting phasing to prevent piston‑to‑valve contact and to stabilize idle, especially on domestic V8s with AFM/DOD systems that are often removed during a cam swap.

Mechanical Path: From Lobes to Valves

Whether pushrod or overhead-cam, the cam lobe’s shape is translated into valve motion through specific hardware. The common components and their roles are outlined below.

• Camshaft and Lobes: The “program” that dictates timing and lift.
• Lifters/Tappets: Follow the lobe; hydraulic types self-adjust, solid types allow precise lash.
• Pushrods and Rocker Arms (pushrod engines): Convert lifter motion into valve actuation and set ratio for effective lift.
• Valve Springs and Retainers: Control valve motion and prevent float at high rpm; must match cam aggressiveness.
• Timing Chain/Belt/Gears: Synchronize cam with crank; phasers add variable timing on VVT engines.

Every link in this chain must be spec’d for the cam. Insufficient spring pressure or weak hardware can cause valve float, contact, or failure at high rpm.

What Changes When You Install a Bigger Cam

Beyond sound, a cammed engine behaves differently across the rev range. Here are the typical effects you can expect.

• Powerband Shift: Torque peak moves higher; top‑end power rises if heads and intake support flow.
• Idle Quality and Vacuum: Idle becomes rougher; vacuum drops, affecting brakes, PCV, and HVAC controls.
• Fueling and Timing Needs: Requires ECU recalibration or carb re-jetting to stabilize idle and part‑throttle.
• Emissions and Economy: Generally worse at idle/low load; overlap can raise hydrocarbons and hurt fuel economy.
• Drivetrain Matching: May need a looser torque converter (automatics), shorter gearing, and stronger valvetrain.

These changes are not drawbacks if the combination is planned; they are tradeoffs that align the engine’s character with its purpose, from street performance to track use.

Supporting Mods That Make a Cammed Build Work

A cam alone rarely delivers its full potential. The following upgrades often accompany a successful cam install.

• Valve Springs, Seats, and Seals: Correct seat pressure and travel to prevent coil bind and float.
• Pushrods and Rockers: Proper length and ratio, trunnion upgrades for stability in high‑rpm V8s.
• Cylinder Heads and Intake: Port flow and manifold tuning that match cam duration and target rpm.
• Exhaust: Long‑tube headers and low‑restriction exhaust to exploit added overlap and scavenging.
• ECU/Carb Tuning: Idle airflow, fuel maps, ignition timing, and sometimes cam phaser tables.
• Drivetrain: Higher-stall converter, clutch with appropriate torque capacity, and gear ratio changes.
• Fuel System: Pump/injector capacity to support new airflow, especially with power adders.

When these parts are matched to the cam’s profile and the vehicle’s mission, the package drives better and makes more reliable power.

Tuning: The Critical Final Step

After installation, calibration determines how livable the setup is day to day. The key adjustments are outlined here.

• Idle Control: Raise idle speed, adjust throttle body airflow, and tune proportional–integral control for stability.
• Fuel Maps: Enrich idle and low‑rpm cells to compensate for overlap-induced dilution; refine transient fueling.
• Ignition Timing: More advance at idle can smooth lope; optimize spark at WOT for knock-safe power.
• VVT Limits (if equipped): Set safe phaser limits to avoid valve contact and refine torque curve.
• Diagnostics/Readiness: Ensure O2, catalyst, and misfire monitors complete if street-legal operation is required.

Good tuning can turn a temperamental build into a street-friendly performer while unlocking much of the cam’s promised power.

Compression, Fuel, and Power Adders

Cam duration changes dynamic compression. Longer intake duration often benefits from slightly higher static compression to restore low‑rpm response. Forced induction pairs well with wider LSA, moderate duration, robust springs, and careful heat management to avoid reversion and detonation.

Reliability and Risks

Cammed engines can be daily-drivable and reliable when built correctly. The risks—valve float, coil bind, piston‑to‑valve contact, wiped lobes, and oiling issues—are largely avoided with correct parts, break‑in procedures (especially on flat-tappet cams with proper zinc/phosphorus oil), and conservative rev limits.

Legal and Emissions Considerations

In many regions, aggressive cams can cause emissions test failures due to higher hydrocarbons and altered OBD readiness. CARB‑certified parts are limited, and U.S. enforcement on tampering has tightened in recent years. If street legality matters, consult local regulations, keep factory emissions equipment intact, and choose milder profiles or certified packages.

Common Myths, Clarified

There are frequent misconceptions about cams. The points below separate myth from reality.

• “Lope equals power.” Not necessarily—lope reflects overlap. Power comes from overall airflow and combustion efficiency.
• “Big cams kill street manners.” Only if mismatched; careful spec’ing and tuning can retain good drivability.
• “You can drop in a cam without other changes.” Possible with mild profiles, but springs and tuning are almost always required.
• “VVT makes big cams obsolete.” VVT broadens torque, but profile choice still governs the ceiling of airflow and power.

Understanding these nuances helps set realistic expectations and guides better component choices for your goals.

Summary

A cammed engine uses a performance camshaft to alter when and how far valves open, trading idle smoothness and low‑rpm manners for stronger high‑rpm breathing and power. The core variables—lift, duration, and lobe separation—reshape the torque curve by changing valve overlap and timing through the four-stroke cycle. Success comes from matching the cam to the heads, compression, exhaust, gearing, and intended use, then finishing with careful tuning and, where applicable, VVT management. Done right, a cammed setup delivers the sound and surge enthusiasts want with reliability that suits the street, strip, or track.

Does camming an engine make it faster?

With that said, aftermarket cams are designed for high-end performance, so you can typically expect to experience faster speeds after camming a truck. Are Bigger Cams More Powerful? Yes. A bigger cam will open the intake valve wider, allowing more fuel and air into the cylinder.

How does camming an engine work?

The camshaft consists of a cylindrical rod running the length of the cylinder bank with a number of cams (discs with protruding cam lobes) along its length, one for each valve. As the cam rotates, the lobe presses on the valve (or an intermediate mechanism), thus pushing it open.

What’s the point of camming a car?

“Camming” a car involves upgrading its camshaft to increase engine power and performance, often resulting in a distinct, aggressive engine sound, especially at idle. A performance camshaft is designed with different lobe lift and duration, allowing more air and fuel into the cylinders at higher RPMs for increased horsepower, though it can also cause a choppy idle and may reduce efficiency at low RPMs.
 
This video explains what a camshaft is and how it works in an engine: 57sCarlyle’s PicksYouTube · Feb 18, 2014
How Camming Works

• Engine Breathing: The camshaft is a rotating shaft with lobes (egg-shaped protrusions) that push open the intake and exhaust valves in the engine’s cylinders. 
• Altering Valve Events: A cam swap changes the camshaft’s profile to alter the timing, duration (how long valves stay open), and lift (how far they open) of the valves. 
• Increased Airflow: A performance camshaft typically increases valve lift and duration, allowing more air to enter the cylinders during the intake stroke and more exhaust gases to exit. 

Benefits of Camming

• More Power: By allowing more air and fuel into the engine, a cam upgrade increases horsepower and improves the engine’s power band, particularly at high RPMs. 
• Distinct Sound: The increased valve overlap, where intake and exhaust valves are open simultaneously, creates a characteristic “chop” or “rumble” sound at idle, a popular feature for many enthusiasts. 
• Improved Throttle Response: A cam can significantly improve throttle response, making the engine feel more powerful when you press the accelerator. 

Tradeoffs and Considerations

• Choppy Idle: Performance cams often result in a rougher, “choppy” idle compared to a stock engine, which may be a con for daily drivers. 
• Low-End Power: Some aggressive cams may reduce engine efficiency and power at lower RPMs, as the engine’s ability to breathe efficiently is compromised. 
• Complete System: For maximum benefit, a cam upgrade should often be paired with other supporting modifications, such as a performance tune, and potentially stronger engine components to handle the increased power and demands. 

What does a Cammed engine do?

A cam (camshaft) controls an engine’s intake and exhaust valves, precisely opening and closing them in sync with the crankshaft’s rotation to allow fuel and air in and exhaust gases out of the cylinders at the correct times in the four-stroke cycle. The specific timing, duration, and lift of the valves, determined by the camshaft’s profile and timing, dictate the engine’s power, idle quality, and overall performance characteristics.
 
How it works

1. Rotation: The camshaft is driven by the crankshaft via a timing belt or chain, ensuring it rotates at exactly half the speed of the crankshaft in a four-stroke engine. 
2. Lobes: The camshaft has precisely shaped lobes (protrusions) that rotate with it. 
3. Valve Actuation: As the cam lobes rotate, they press down on valve followers or rocker arms, which in turn push the valves open. 
4. Valve Closing: Valve springs then close the valves once the cam lobe passes and no longer presses down on the follower. 
5. Synchronization: This controlled opening and closing ensures the four-stroke combustion cycle proceeds efficiently: 
   • Intake Stroke: The intake valve opens, allowing the air-fuel mixture into the cylinder. 
   • Compression Stroke: Both valves are closed, and the piston moves up to compress the mixture. 
   • Power Stroke: The spark plug ignites the mixture, forcing the piston down. 
   • Exhaust Stroke: The exhaust valve opens, allowing the burnt gases to exit the cylinder. 

Impact on engine performance

• Mild Cams: Opens in new tabHave gentle lobe profiles, leading to smooth idling, good fuel economy, and easy starts, but less peak power. 
• Performance Cams: Opens in new tabHave more aggressive lobes that open valves wider and for longer durations, allowing more air and fuel into the cylinders for increased power and higher RPM capability. However, this can result in a rougher idle and decreased low-speed performance. 
• Variable Valve Timing (VVT): Opens in new tabModern systems allow the camshaft’s timing to be adjusted on the fly, improving both power and fuel efficiency by optimizing valve operation for different engine conditions.