How “camming” an engine works—and what really changes when you swap or tune a camshaft

Camming an engine means changing how and when the valves open by swapping the camshaft or adjusting its phasing; this reshapes the powerband, often trading low‑RPM smoothness and vacuum for more high‑RPM horsepower. In practice, the cam’s lift, duration, and lobe separation angle determine airflow timing, and the right combination—matched with proper springs, tuning, and supporting parts—can deliver substantial gains with acceptable drivability and reliability.

What enthusiasts mean by “camming”

In enthusiast slang, “camming” usually refers to installing a performance camshaft with different lobe profiles. On many modern engines, it also includes recalibrating variable valve timing (VVT) to advance or retard the cam(s) relative to the crankshaft. Either way, you’re changing valve events to improve cylinder filling and scavenging in a chosen RPM range.

The camshaft’s job

The camshaft has egg‑shaped lobes that convert rotation into the precise lift and timing that open and close intake and exhaust valves. In pushrod engines (OHV), lobes act on lifters, pushrods, and rocker arms. In overhead‑cam (SOHC/DOHC) engines, lobes act directly on followers or lifters over the valves. Correct timing is synchronized by the timing belt/chain/gears relative to crankshaft rotation.

The key cam specs—and what they do

The main camshaft specifications determine how the engine breathes and where it makes power. Understanding these helps explain how camming changes performance.

• Valve lift: How far the valve opens. More lift can increase airflow, especially with good cylinder heads, but needs stronger springs and adequate retainer/seal clearance.
• Duration (advertised and at 0.050″): How long the valve stays open. More duration typically shifts power higher in the RPM range and reduces low‑end torque and vacuum.
• Lobe Separation Angle (LSA): Angle between intake and exhaust lobe centers. Tighter LSA (e.g., 106–110°) increases overlap for stronger mid/high‑RPM torque and “lope,” but hurts idle and emissions; wider LSA smooths idle and broadens torque.
• Intake/Exhaust Centerlines and phasing: Where peak lobe lift occurs relative to Top Dead Center. Advancing intake timing boosts low‑end; retarding favors top‑end.
• Overlap: The period both valves are open. Helps scavenging at high RPM but can cause reversion and rough idle at low RPM.
• Ramp rate/acceleration: How quickly a lobe lifts the valve. Aggressive ramps add area under the curve but stress valvetrain components.
• Lash/preload specification: Required clearance (solid cams) or preload (hydraulic lifters) for correct operation and durability.

Together, these parameters set the engine’s airflow “window.” A cam that’s ideal for 6,800 RPM road racing will feel soggy around town; a mild street cam emphasizes idle stability and midrange over peak power.

What changes when you install a performance cam?

Swapping to a hotter cam alters pressure waves and airflow timing, which changes the torque curve and drivability characteristics. Expect tradeoffs you should plan around.

• Powerband shift: Longer duration and tighter LSA move torque and horsepower higher, increasing top‑end at the expense of low‑RPM torque.
• Idle quality and vacuum: More overlap typically produces a choppier idle and lower manifold vacuum, affecting brakes, HVAC controls, and PCV function.
• Tuning needs: Fuel, spark, idle airflow, and cam phasing (if VVT) must be recalibrated. Untuned, cams can run lean/rough and trigger misfire or emissions codes.
• Dynamic compression: Longer duration/overlap bleed off low‑RPM cylinder pressure; higher static compression or advanced intake centerline may be needed to regain response.
• Valvetrain stress: Higher lift and faster ramps demand better springs, precise geometry, and adequate oiling to avoid float and wear.
• Emissions and inspections: Increased overlap raises hydrocarbons and can jeopardize OBD readiness; street legality varies by jurisdiction.
• Driveline matching: Big cams may want a higher‑stall torque converter (autos), shorter gearing, and a freer‑flowing exhaust and intake.
• Boosted engines: Turbo/supercharged setups often prefer wider LSA and moderate duration to control overlap and keep boost in the cylinder.

The right cam is part of a package: cylinder heads, compression ratio, intake/exhaust, and calibration must complement the lobe design to realize gains without sacrificing reliability.

Variable valve timing and “cam tuning” on modern engines

Many late‑model engines (e.g., GM VVT, Ford Ti‑VCT, Toyota VVT‑i, BMW VANOS) can advance/retard intake and/or exhaust cams on the fly. Tuning VVT changes overlap and the timing of valve events across RPM and load, improving torque spread and efficiency. Unlike a hardware cam swap, phasing can’t change maximum lift or duration—only when those events occur—so it fine‑tunes the curve rather than redefining it. Some builds use phaser limiters or lockouts to control excessive advance/retard with big aftermarket cams.

Supporting parts and prep: what you typically need

A cam swap often requires upgraded valvetrain components and attention to clearances to keep the engine reliable at higher lift and RPM.

• Valve springs matched to lift and ramp rates (and often new retainers/locks); check coil bind and installed height.
• Valve stem seals with adequate retainer clearance for high lift.
• Lifters (hydraulic or solid; roller or flat‑tappet) compatible with the cam; consider new pushrods for correct length and stiffness.
• Trunnion/rocker upgrades on some OHV platforms (e.g., LS) to handle higher loads.
• Timing set, phaser limiter/lockout (if VVT), and fresh cam bearings where applicable.
• Head gaskets/bolts or studs if heads must come off; new front cover and crank seals.
• Higher‑flow intake/exhaust and, where appropriate, higher stall converter or shorter gearing.
• ECU tuning capability and wideband O2 for calibration.

Skimping on springs, geometry, or calibration is the fastest way to wipe lobes, float valves, or lose the gains you’re chasing.

Installation highlights and best practices

Cam swaps range from straightforward (OHV V8 in‑chassis) to complex (transverse DOHC timing). Precision matters: measure, mock up, and verify before final assembly.

1. Define goals and select the cam for your heads, compression, gearing, and use case; get spring and phaser guidance from the cam grinder.
2. Disassemble methodically; lock the crank at TDC, mark timing references, and maintain cleanliness to protect bearings.
3. Degree the cam using a wheel and dial indicator to confirm intake centerline and verify lobe events match the card.
4. Check piston‑to‑valve and retainer‑to‑seal clearance through the full RPM range; typical P‑V minima are ~0.080″ intake/0.100″ exhaust on performance builds.
5. Set lifter preload (hydraulic) or lash (solid) per spec; verify rocker geometry and pushrod length with pattern checks.
6. Install the timing set/phasers; apply proper torque and, where required, perform phaser relearn procedures after startup.
7. Reassemble with fresh gaskets/seals; prime the oiling system before first fire.
8. Load a safe base tune; stabilize idle, fueling, and spark, then complete fine tuning under controlled conditions.
9. Break in if required (see below), monitor for leaks/noise, and datalog knock, trims, and misfire counts.

Careful degreeing and clearance checks prevent catastrophic interference, especially in high‑lift or tight‑LSA applications and on interference engines.

Flat‑tappet vs. roller, hydraulic vs. solid: important differences

Cam and lifter types change break‑in needs, maintenance, and limits on ramp rates and lift.

• Flat‑tappet cams require proper break‑in: use assembly lube and high‑zinc/phosphorus (ZDDP) oil, run 20–30 minutes at 2,000–2,500 RPM immediately on first start, and avoid long idles early on.
• Roller cams don’t need the same lobe break‑in, but new lifters and springs still benefit from careful initial operation and oil quality.
• Hydraulic lifters self‑adjust (quieter, lower maintenance) but can pump up at very high RPM; solids support higher RPM with set lash but need periodic adjustment.
• Aggressive lobes demand higher spring rates; balance control with friction and wear for longevity.

Choosing the lifter style affects not just power potential but also noise, maintenance, and how forgiving the setup is to small tuning or geometry errors.

Common myths and realities

Cam choices are full of folklore; here’s what holds up.

• Bigger isn’t always better: too much duration kills street drivability and can reduce average power in the usable range.
• “Lopey” idle doesn’t equal fast: overlap makes sound, not guaranteed speed—head flow, compression, and tuning make the combo work.
• Heads and exhaust matter: a cam can’t fix restrictive ports or a choking exhaust; the system must flow.
• No‑tune cam swaps are risky: even “drop‑in” cams benefit from calibration for idle airflow, spark, fueling, and VVT.
• Boost needs different lobes: forced‑induction cams typically reduce overlap to keep charge in the cylinder and manage turbine/compressor efficiency.

Evaluate average torque in your target RPM band rather than peak numbers alone; the fastest car isn’t always the one with the lumpiest idle.

Risks, legality, and reliability considerations

Large cam changes can push engines past OEM margins. Ensure sufficient valve‑to‑piston clearance, spring control to redline, oil quality, and cooling capacity. For street cars, check emissions rules: some regions require CARB‑certified parts and OBD readiness; excessive overlap can prevent monitors from setting. Warranty coverage may be affected by non‑OEM cams and tunes.

Cost and time: what to expect

Parts costs vary widely. A typical pushrod V8 cam kit (cam, springs, seals, pushrods, gaskets) often runs $800–$1,800; roller lifters add more. DOHC kits can exceed $2,000 due to multiple cams and timing components. Professional labor ranges from 6–12 hours for many OHV platforms and 12–20+ hours for tight DOHC applications. Dyno tuning commonly adds $400–$1,000. Budget for fluids, seals, and potential head removal on interference engines.

Bottom line: how camming makes power

Camming works by optimizing valve events so the engine breathes better in the RPM range you care about. Lift increases potential flow, duration and overlap tailor where that flow helps most, and phasing fine‑tunes torque and emissions. The best results come from a matched package—cam profile, springs, heads, compression, intake/exhaust, and ECU tuning—built for a clearly defined use.

Summary

Changing or tuning a camshaft alters valve lift, duration, and timing to reshape airflow and pressure waves, trading low‑RPM civility for higher‑RPM power when desired. Choose specs around your heads, compression, gearing, and intended use; upgrade springs and supporting parts; degree and measure everything; and calibrate the ECU (and VVT if equipped). Done correctly, camming delivers meaningful, reliable gains; done haphazardly, it harms drivability, emissions, and longevity.

What is the point of camming an engine?

“Camming”, or replacement of the engine’s camshaft(s), helps the engine make more power by altering valve lift, timing, and duration. Certain camshaft profiles help the engine breathe better at certain RPM ranges, usually up high in the case of a performance cam.

Does camming an engine add horsepower?

Yes. Adjusting the camshafts so the cams are slightly ahead or behind will alter the engine’s performance. Advancing the timing will cause the fuel intakes to open and close earlier, which improves low-end torque. Conversely, retarding the cam will improve high-end horsepower at the expense of low-end torque.

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. 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. 2. Lobes: The camshaft has precisely shaped lobes (protrusions) that rotate with it. 
3. 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. 4. Valve Closing: Valve springs then close the valves once the cam lobe passes and no longer presses down on the follower. 
5. 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. 

What are the cons of camming a car?

In our own demo car we picked up 100 wheel horsepower going to a large cam but what that results in is a loss of fuel economy, and a loss of power and torque below around about 3000 RPM and you’re also going to get the car pushing a little bit when it’s in gear because the idle speed needs to be higher so there is a …