What Putting a Cam in an Engine Does

Installing a different camshaft changes when and how far the intake and exhaust valves open, reshaping the engine’s airflow and shifting the torque/power curve—often adding high‑rpm horsepower while sacrificing low‑rpm smoothness, vacuum, fuel economy, and emissions unless paired with proper tuning and supporting parts. In practice, “putting a cam in” is a strategic way to retarget an engine’s character for street, track, or towing.

What the Camshaft Actually Does

The camshaft uses egg-shaped lobes to open and close intake and exhaust valves in sync with crankshaft rotation. By altering valve timing (when valves open/close), lift (how far they open), and overlap (how long intake and exhaust are open together), a cam controls cylinder filling and scavenging. Those valve events determine volumetric efficiency across the rev range, which is why a cam profile can move the engine’s sweet spot up or down the rpm band.

How a Performance Cam Changes Engine Behavior

Swapping to a performance cam typically emphasizes airflow at certain engine speeds. A “bigger” cam (more duration and often more lift) increases high‑rpm breathing, while a “smaller” cam favors low‑rpm torque and drivability. The change is rarely neutral: gains in one area usually trade off against another.

The following points outline the most common, real-world outcomes when you install a performance cam.

• Powerband shift: Longer duration and overlap move peak torque and power to higher rpm, improving top-end pull but softening low-end response.
• Idle quality: Increased overlap causes the characteristic “lope” at idle and reduces manifold vacuum, which can affect brakes, HVAC controls, and automatic transmissions.
• Fuel economy and emissions: More overlap tends to waste some mixture at low rpm, typically lowering mpg and worsening emissions without careful calibration.
• Sound: Aggressive cams are louder and choppier at idle, which some owners want, but sound is not a guarantee of speed.
• Tuning requirement: ECU/PCM recalibration is often mandatory to correct fueling, spark, idle, and cam phasing (if VVT), and to keep OBD monitors functional.
• Component stress: Higher lift and rpm increase valvetrain loads, demanding stronger springs, pushrods, retainers, and sometimes rocker arms.

Taken together, a cam swap customizes the engine’s personality; the best results come from matching the cam to how the vehicle is driven and from supporting the change with appropriate hardware and tuning.

Key Camshaft Specs That Matter

Several specifications describe a cam’s behavior. Understanding them helps predict how the engine will respond and whether the rest of the build should change to suit.

• Lift: Maximum valve opening. More lift can increase airflow if the cylinder head can use it; too much lift without upgraded springs risks coil bind or valve float.
• Duration (advertised and at 0.050″): How long a valve stays open. Higher duration generally raises the rpm where the engine breathes best.
• Lobe Separation Angle (LSA): Degrees between intake and exhaust lobe centers. Narrow LSA (e.g., 106–110) increases overlap and sharpens mid/top response with rougher idle; wide LSA (e.g., 112–116) broadens torque and improves idle/vacuum.
• Intake Centerline/Cam Advance: Installing the cam advanced or retarded shifts the torque curve; advancing usually helps low/midrange, retarding can favor top-end.
• Overlap: The period both valves are open. More overlap aids scavenging at high rpm but hurts idle quality and emissions.
• Valve Events: The specific open/close points relative to crank degrees dictate dynamic compression and detonation tendency.

No single spec tells the whole story; consider lift, duration, LSA, and installed centerline together, and confirm that head flow, piston design, and spring capability align with the chosen profile.

Match the Cam to the Combination

The “right” cam depends on the whole package: engine size, compression, heads, intake and exhaust, converter/gearing, weight, and intended use. Picking a cam in isolation is a common cause of disappointment.

• Compression ratio: Bigger cams bleed off low-rpm cylinder pressure; higher static compression often helps recover torque and throttle response.
• Cylinder head flow: Heads must support the lift and airflow the cam demands; otherwise, extra lift/duration adds noise without power.
• Intake/exhaust: Free-flowing manifolds and headers complement longer duration; restrictive systems mute gains.
• Converter and gears (automatics): Higher-stall converters and shorter axle gears help keep the engine in the new, higher powerband.
• Vehicle mass and use: Heavy daily drivers favor mild profiles; light cars or track builds can tolerate aggressive timing.
• Valvetrain stability: Springs matched to the cam’s lift and ramp rates prevent float and protect the engine at elevated rpm.
• Forced induction: Turbo/supercharged setups often prefer wider LSA and moderate overlap to keep boost in the cylinders.
• Variable Valve Timing (VVT): Many modern engines can move cam timing on the fly; aftermarket cams must be VVT-compatible and tuned accordingly.

When all the supporting pieces are aligned, a cam swap transforms the engine predictably; when they are mismatched, drivability and reliability suffer and the expected power fails to materialize.

Engine Types and Installation Notes

How you “put a cam in” depends on engine architecture. Pushrod (OHV) engines usually have a single cam in the block and use lifters and pushrods, while OHC/DOHC engines have one or two cams in the head and often include variable cam timing.

• Pushrod/OHV: Common in American V8s. Roller cams are widely used; flat-tappet cams require careful break-in and high-zinc oil. Degreeing the cam is strongly recommended.
• OHC/DOHC: Cam(s) live in the head; belt/chain service is more involved and demands precise timing tools. Many are interference engines—verify piston-to-valve clearance.
• VVT-equipped engines: Cam phasers can add or subtract timing dynamically; aftermarket cams may need limiter/lockout kits and specific tuning to avoid errors and interference.

Regardless of layout, accurate installation, proper spring pressures, and confirmed clearances are essential to prevent failure and to achieve the cam’s intended performance.

Risks, Requirements, and Legality

A cam swap is as much a calibration and systems job as a mechanical one. Skipping the supporting steps can mean worse performance than stock—and possible engine damage.

• ECU calibration: Required for idle control, fueling, spark, rev limits, and—on VVT engines—phaser control and diagnostics.
• Valve springs and hardware: Match to lift and ramp rates; inspect for coil bind and set correct installed height and seat/open pressures.
• Degreeing the cam: Verifies the cam’s actual position; manufacturing tolerances and timing set variations make this step critical.
• Piston-to-valve clearance: Check with clay or dial indicators, especially with high lift, tight LSA, milled heads, or thinner gaskets.
• Idle vacuum: Low vacuum may require an auxiliary vacuum pump or hydroboost for power brakes, and reconfiguration of PCV systems.
• Fuel and detonation: Changes in dynamic compression and heat may require higher octane and careful spark mapping.
• Noise and longevity: Aggressive lobes increase wear and valvetrain noise; quality parts and correct lash/preload are vital.
• Break-in: Flat-tappet cams demand break-in with high-ZDDP oil and specific procedures; roller cams still need careful first start.
• Emissions and compliance: In many regions, non-certified cams constitute emissions tampering and can fail inspections or void warranties.

Addressing these items up front prevents surprises and helps the engine deliver the gains you’re paying for while staying safe and compliant where required.

Examples: What You Can Expect

Power gains vary widely by engine, support parts, and tune. These illustrative scenarios show typical trade-offs for naturally aspirated V8s of similar displacement; results differ for smaller engines and forced induction.

• Mild street cam (e.g., 210–218° @0.050″, ~0.500″ lift, 112–114 LSA): Strong low-mid torque, near-stock idle, modest top-end gain; minimal converter change; good daily drivability.
• Hot street/strip cam (e.g., 226–236° @0.050″, ~0.550–0.600″ lift, 110–112 LSA): Noticeable lope, reduced vacuum, clear mid/high-rpm gains; needs springs, tune, headers, higher-stall converter, and gears.
• Turbo-friendly cam (e.g., moderate duration, 114–118 LSA): Smoother idle, controlled overlap to keep boost in-cylinder; strong area under the curve once on boost; pairs well with efficient intercooling and careful timing.

Choosing among these profiles comes down to how you drive, where you want the engine to feel strongest, and what supporting parts you’re willing to add.

Summary

Putting a cam in an engine alters valve timing and lift to redirect airflow and shift the torque curve. A well-matched, well-tuned cam can unlock meaningful power and responsiveness in the desired rpm range, while a mismatched or untuned setup can hurt drivability, economy, emissions, and reliability. Select the cam with the whole combination in mind, verify clearances, upgrade the valvetrain as needed, and calibrate the ECU to realize the gains safely.