Why the Camshaft Is the Heart of AMC AMX Performance

The AMC AMX, produced from 1968 to 1970, is a genuine American muscle car icon. Its lightweight body and potent AMC V-8 engines made it a formidable competitor on both street and strip. However, even the most legendary factory engines were restricted by emission regulations and production cost constraints, leaving substantial untapped performance potential locked inside. A camshaft upgrade is often the single most effective modification for unlocking that potential.

The camshaft dictates the engine’s breathing cycle. By altering valve lift, duration, and lobe separation angle, a performance camshaft can dramatically shift the power band higher, increase peak horsepower, and improve throttle response. For AMC AMX owners, a well-chosen cam from a trusted manufacturer like Comp Cams can yield gains of 30 horsepower or more while retaining excellent street manners when paired with complementary modifications.

Understanding Camshaft Fundamentals for the AMC V-8

Before diving into specific upgrades, it’s essential to grasp how camshaft specs affect engine behavior. The AMC V-8 (304, 343, 360, 390, 401) shares a common block architecture but different stroke and bore combinations. Choosing the wrong cam can lead to poor idle, low vacuum, and disappointing power. Key parameters include:

  1. Intake Duration (degrees): Determines how long the intake valve stays open. Longer duration shifts the power band to higher RPM.
  2. Exhaust Duration (degrees): Similar for exhaust. Asymmetrical durations are used to fine-tune overlap for specific RPM ranges.
  3. Valve Lift (inches): How far the valve opens. Higher lift improves airflow but may require spring upgrades to prevent coil bind.
  4. Lobe Separation Angle (LSA): Affects overlap and idle quality. A tight LSA (108°–110°) gives a choppy idle and strong top-end; a wider LSA (112°–114°) smooths the idle and improves vacuum for accessories.
  5. Duration @ .050 inch lift: The industry standard for comparing cams, because it excludes the “slow ramps” at the top and bottom. A “212° @ .050” cam is considered mild; “242° @ .050” is very aggressive.

For the AMC AMX, aftermarket camshafts are typically designed for non-roller lifter engines (hydraulic flat tappet or solid flat tappet), though roller retrofit cams are available for maximum performance. Comp Cams offers all three types.

Why Comp Cams Dominates the AMC Camshaft Market

Comp Cams, founded in 1976, has become the gold standard for aftermarket camshaft technology. Their extensive catalog includes camshafts specifically ground for AMC V-8s, with detailed dyno data to back up claims. Key advantages of Comp Cams for AMC AMX owners:

  • Proprietary lobe designs: Controlled-milling technology creates lobes with faster opening ramps, increasing “area under the curve” for more power across the RPM range.
  • Precision manufacturing: Each cam is made from SAE 8620 steel (or chilled iron for flat tappet) with case-hardened surfaces to resist wear.
  • Vehicle-specific recommendations: Comp Cams provides part numbers, installation kits, and spring recommendations tailored to AMC engines, eliminating guesswork.
  • Support for all stages: From mild street cams to full race profiles, Comp Cams covers the spectrum. Their “Xtreme Energy,” “High Energy,” and “Magnum” series all have AMC specific grinds.

For a comprehensive look at Comp Cams’ full AMC lineup, visit their official website.

Top Comp Cams Upgrades for AMC AMX Engines

The following camshafts represent proven upgrades for the most common AMX engine displacements. Dyno results from real-world installations show gains ranging from 20 to 40 horsepower over stock, with the 30-hp improvement being a realistic benchmark for a moderate street build.

Comp Cams Xtreme Energy Camshaft (Part #CL12-216-2 for AMC V-8)

This hydraulic flat tappet cam features 212°/218° duration @ .050 inch and .444/.470 inch lift with a 112° LSA. It is ideal for 343 to 401 engines with stock or mild heads, 9.0–10.0:1 compression, and low-rise intake manifolds. The Xtreme Energy design provides a broad torque curve from 1500–5500 RPM while adding a noticeable idle lope. Many owners report a 25–30 horsepower increase when combined with a dual-plane intake and headers. It retains good manifold vacuum for power brakes and air conditioning.

Comp Cams High Energy Camshaft (Part #CL12-210-4)

A milder option, the High Energy cam offers 204°/214° duration @ .050 with .430/.444 lift on a 112° LSA. This is the perfect upgrade for a stock 304 or 360 AMX that sees daily driving duty. It boosts torque from idle to 4500 RPM with minimal loss of low-end vacuum. Gains of 15–20 horsepower are typical. The High Energy cam is also compatible with factory valve springs (up to .460 inch lift) and does not require aftermarket pushrods, making it a budget-friendly entry into cam upgrades.

Comp Cams Magnum Camshaft (Part #CL12-222-2)

For enthusiasts seeking maximum power, the Magnum series delivers a 224°/230° duration at .050, with .477/.488 inch lift on a 110° LSA. This is a hydraulic flat tappet design best suited for 390 and 401 engines with aftermarket aluminum heads, high-compression pistons (10.5:1 or more), and a single-plane intake. Expect a choppy idle at 800–900 RPM and a power band from 2500–6500 RPM. Gains of 35–40 horsepower are achievable, but the cam requires upgraded valve springs, retainers, and pushrods to prevent valvetrain instability above 6,000 RPM.

For those considering a roller conversion, Comp Cams offers retrofit hydraulic roller camshafts (e.g., part #CL12-225-5) that provide even faster ramp accelerations and reduced friction. However, these require conversion lifters, a special timing set, and often head modifications. Roller cams can add another 10–15 horsepower over an equivalent flat tappet grind.

Supporting Modifications Needed for 30+ Horsepower Gains

Installing a new camshaft in an AMC AMX without addressing the rest of the engine’s airflow is like putting a high-flow carburetor on a clogged air cleaner. To realize the full 30-horsepower improvement, these supporting mods are strongly recommended:

  • Upgraded valve springs: Comp Cams recommends a specific spring kit for each cam. Stock springs are typically too weak above .450 inch lift and will cause valve float.
  • High-performance pushrods: Stock pushrods may flex or fail under aggressive ramps. Chrome-moly pushrods (5/16 inch diameter) are a worthwhile upgrade.
  • Double-roller timing chain: The stock nylon-tooth chain is a weak point on AMCs. A Cloyes or Comp Cams double-roller set adds reliability and allows accurate cam timing.
  • Intake manifold upgrade: A dual-plane intake (Edelbrock Performer or Weiand Stealth) complements the Xtreme Energy cam. For the Magnum cam, a single-plane (Edelbrock RPM Air-Gap) is preferred.
  • Carburetor or fuel injection tuning: An aftermarket carburetor (Holley 750 cfm or 800 cfm) with adjustable air bleeds and a vacuum-secondary design works well. If running fuel injection, the mass airflow sensor and injector pulse width will need recalibration.
  • Headers: Long-tube headers (1¾ inch or 1⅝ inch primary) reduce exhaust restriction and let the cam deliver its full potential. For AMCs, header choices are limited but companies like Hooker and Flowtech offer AMX-specific units.

The combination of a Comp Cams Xtreme Energy cam, Edelbrock Performer intake, 750 cfm carb, and headers consistently produces 300–330 horsepower on a 360 AMX, a solid 30–50 hp over the factory rating. For detailed dyno charts, consult the AMC Performance resource site.

Installation Guide: Setting Up Your AMC AMX Camshaft Correctly

A camshaft swap is an intermediate-level job requiring patience and precision. Below is a step-by-step approach specific to the AMC V-8. Always refer to the factory service manual for torque specs and special tools.

Preparation and Parts Needed

  • Complete Comp Cams camshaft with recommended lifter set (flat tappet or hydraulic roller).
  • New timing set (double-roller) with multi-keyed crank sprocket for degreeing.
  • Valve spring compressor and new seals.
  • Engine assembly lube (for cam lobes and lifter faces).
  • Degree wheel and dial indicator (for verifying cam timing).
  • New gaskets (timing cover, water pump, intake manifold).

Step 1: Remove Front Engine Components

Drain the coolant and remove the radiator, fan, alternator, and belts. Take off the harmonic balancer (use a puller) and the timing chain cover. Note the position of the camshaft thrust plate screws.

Step 2: Remove Old Cam and Lifters

Remove the intake manifold, valley pan, and rocker arms. Identify each lifter and lift them out intact to avoid mixing with the cam lobes (flat tappet lifters need to be kept in order). Withdraw the camshaft carefully through the front of the block—ensure the cam bearings are in good condition. Replace timing chain and gears. If the cam lock plate is worn, install a new one.

Step 3: Degree the New Camshaft

Install the new Comp Cams cam with a new timing set. Do not rely on the dots stamped on the sprockets alone—use a degree wheel to confirm intake and exhaust lobe centerlines. This step is critical; a misaligned cam may cause valve-to-piston clearance issues. Set the camshaft to the recommended (106°–110° intake centerline) with the multi-keyway crank sprocket.

Step 4: Install Lifters and Pushrods

Coat each lifter foot with assembly lube and install them in their original positions. For new lifters on a new cam, you must prime the oil galleries by rotating the engine with a drill motor on the oil pump shaft before starting. Install pushrods, rocker arms, and adjust preload according to Comp Cams specs (usually ½ to ¾ turn past zero lash for hydraulic lifters).

Step 5: Upgrade Valve Springs and Install Intake

Remove old valve springs (cylinder head can be on or off the engine) and install new Comp Cams springs matched to the cam profile. Check installed height and shim if needed. Reassemble the intake manifold with proper sealant, then install the timing cover, balancer, and accessories.

Break-In Procedure

Prime the oil system by cranking with the distributor out until oil flows at the pushrods. Start the engine and run it at 2000–2500 RPM for 20 minutes, varying the RPM slightly but never idling. Flat tappet cams are especially sensitive to break-in; a failure here can ruin the cam lobes instantly. After break-in, change the oil and filter, and inspect the oil for metal particles. Verify valve lash again once the engine is cold.

Performance Testing and Tuning After the Cam Swap

Once the cam is in and broken in, driving the AMC AMX reveals the transformation. The engine will feel stronger from 2500 RPM onward, with an aggressive exhaust note. To quantify the 30-horsepower gain, consider these testing methods:

  • Chassis dyno measurement: A Dynojet or Mustang dyno provides rear-wheel horsepower and torque curves. A stock 360 AMX typically puts down 200–210 rwhp; after a cam upgrade with supporting mods, expect 230–250 rwhp. That is a genuine 30+ horsepower gain at the wheels, which translates to 40+ at the flywheel after drivetrain losses.
  • Quarter-mile trap speed: Pre-cam, an average 360 AMX runs high 14s at 95 mph. Post-cam, many owners report low 14s at 100 mph, confirming the power increase.
  • Throttle response and drivability assessment: Pay attention to idle quality, off-idle tip-in, and part-throttle surge. A properly tuned Xtreme Energy cam should idle at 750–800 RPM in gear with a steady 10–12 inches of vacuum.

For a real-world example, refer to online forums such as the AMC Forum, where AMX owners have documented their cam swap experiences with Comp Cams products. Many report satisfaction with the Xtreme Energy series for daily-driven street cars and the Magnum series for weekend track events.

Potential Pitfalls and How to Avoid Them

Even with a quality cam from Comp Cams, several issues can compromise the upgrade:

  • Valve-to-piston interference: With high-lift cams (above .500 inch lift), especially in 343 and 304 engines with small combustion chambers, check clearance using clay. Fly-cutting pistons may be needed.
  • Oil pan clearance: Some AMC blocks have a windage tray that may contact the rod bolts if deep-sump pan isn’t used. Not an issue with stock pans, but tall cams requiring high spring pressures may stress the valvetrain.
  • Distributor gear wear: Aftermarket steel camshafts can wear bronze distributor gears in AMCs. Use a hardened gear (MSD or Comp Cams) to avoid failure.
  • Lifter bleed-down: Flat tappet lifters must be properly primed; if not, they can collapse and cause valvetrain noise. Use Comp Cams recommended lifter bleed-down procedure.

For a comprehensive list of AMC V-8 camshaft specifications and compatibility, the American Motors Owners Association maintains a technical library.

Conclusion: Unlock the True Potential of Your AMC AMX

The AMC AMX deserves a powerplant that matches its legendary styling. A Comp Cams camshaft upgrade is one of the most rewarding modifications you can make—it transforms the engine’s character from a mild-mannered cruiser to a snarling performance machine. With careful selection among the Xtreme Energy, High Energy, or Magnum series, and proper installation and tuning, you can reliably achieve a 30-horsepower boost or more. Whether you’re restoring an original 1969 AMX or building a modern pro-touring interpretation, the right camshaft from Comp Cams will bring your AMC V-8 to life again.