The AMC AMX: A Muscle Car Legend Ready for Modern Power

The AMC AMX, produced from 1968 to 1970, stands as one of the most distinctive American muscle cars ever built. With its short wheelbase, lightweight unibody construction, and aggressive styling, the AMX was designed from the factory to compete with the likes of the Chevrolet Corvette and Pontiac GTO. The standard 390 cubic inch V8 produced a respectable 315 horsepower, but for serious enthusiasts, the real potential lies in what these engines can become. Achieving over 400 horsepower with a naturally aspirated AMC V8 is not only feasible but can be done with a well-planned combination of aftermarket parts from industry leaders like Edelbrock and MSD. This detailed cost breakdown will guide you through every major component needed to transform your AMX into a 400+ horsepower street machine that can hold its own against modern performance cars.

Understanding the AMC V8 Platform

Before diving into part costs, it is essential to understand what you are working with. The AMC V8 family includes the 290, 343, 360, 390, and 401 cubic inch engines. The 390 and 401 are the preferred starting points for a 400+ horsepower build because of their larger displacement and stronger bottom ends. However, even a 360 can reach this goal with the right combination of parts. The key limiting factors on the stock AMC engine are the cylinder heads, intake manifold, and ignition system. These are precisely the areas where Edelbrock and MSD excel. Upgrading these components, along with a performance camshaft and proper tuning, will unlock the power you are after. The 400 horsepower target is a sweet spot: it is aggressive enough for serious street performance and occasional track days, yet remains docile enough for street driving if the correct camshaft and compression ratio are chosen.

Engine Block and Short Block Assembly

Starting Point: Core Engine

For this build, we will assume you are starting with a rebuildable AMC 390 or 401 block. A good core engine can cost between $300 and $800 from a salvage yard or private seller. If you do not have an engine, you will need to factor this into your budget. Alternatively, you could purchase a fully rebuilt short block from a reputable engine builder, which will cost between $2,500 and $4,000. For the purposes of this cost breakdown, we will cover the parts needed to rebuild your existing block to handle 400+ horsepower.

Stroker Kit: The Foundation for Torque

The quickest way to increase displacement and torque is with a stroker kit. AMC engines respond exceptionally well to increased stroke. A popular option is a 4.00-inch stroke crank with forged 6.125-inch rods and custom pistons, which will take a 390 to around 410 cubic inches and a 401 to 430+ cubic inches. A quality stroker kit from brands like Eagle or Scat will cost between $1,200 and $2,000. This includes the crankshaft, connecting rods, pistons, rings, and bearings. This is a significant investment, but it is the single most impactful upgrade for building torque and horsepower. If your budget is tighter, you can stay with a stock stroke and focus on cylinder head and camshaft upgrades, but the power ceiling will be lower.

High-Performance Pistons, Rings, and Bearings

Even if you skip the stroker kit, you will need forged pistons to handle the increased cylinder pressure and heat. Hyperutectic cast pistons may suffice for a mild build, but forged pistons are recommended for reliability at 400+ horsepower. Expect to pay between $400 and $700 for a set of forged pistons, $100 to $150 for rings, and $80 to $120 for rod and main bearings. Do not skimp on these components; they are the difference between a reliable engine and one that fails under load.

Oil Pump and Timing Set

A high-volume oil pump is a wise investment at this power level. The stock AMC oil pump is adequate, but a Melling high-volume pump ($80 to $120) ensures consistent oil pressure at high RPM. A double-roller timing chain set is essential for accurate cam timing and durability. Expect to spend $50 to $100 on a quality timing set from Cloyes or a similar brand.

Cost Summary for Short Block Components

  • Core Engine: $300 - $800 (if not already owned)
  • Stroker Kit (optional): $1,200 - $2,000
  • Forged Pistons (non-stroker): $400 - $700
  • Rings: $100 - $150
  • Bearings: $80 - $120
  • Oil Pump: $80 - $120
  • Timing Set: $50 - $100

Cylinder Heads: The Biggest Bang for Your Buck

Why Edelbrock Heads Are the Gold Standard

Stock AMC cylinder heads are the primary bottleneck for power. Their small intake and exhaust ports, combined with inefficient combustion chambers, significantly limit airflow. The most effective single upgrade for an AMC V8 is a set of aftermarket aluminum cylinder heads. Edelbrock offers two outstanding options: the Edelbrock Performer RPM AMC head (part number 60119) and the Edelbrock Victor Jr. head for dedicated race applications. For a 400+ horsepower street engine, the Performer RPM heads are the perfect choice. They flow significantly more air out of the box than ported stock heads, are 50 pounds lighter, and feature improved combustion chambers that are less prone to detonation.

Cost of Edelbrock Performer RPM Heads

A pair of Edelbrock Performer RPM cylinder heads typically ranges from $1,200 to $1,800. This price includes fully assembled heads with stainless steel valves, valve springs, retainers, and keepers. You will need to add the cost of head bolts (ARP, $40 to $60) and a set of head gaskets (Fel-Pro, $50 to $80). The total investment for the cylinder head upgrade, including gaskets and fasteners, is approximately $1,300 to $1,950. This is the single most important expenditure in your 400+ horsepower build. The flow numbers alone can take you from 300 horsepower to 380 horsepower with no other changes to the engine. When paired with the right camshaft and intake, 400 horsepower becomes easily achievable.

Alternative: Porting Stock Heads

If the cost of Edelbrock heads is prohibitive, you could have your stock 390 or 401 heads ported by a professional cylinder head shop. A good porting job, including a three-angle valve job and bowl blending, will cost between $600 and $1,000. The flow results will approach those of the Edelbrock heads, but you will still be limited by the heavier cast iron construction and smaller valve sizes. For the same or slightly less money, the Edelbrock heads are almost always the better choice when considering weight, cooling efficiency, and future resale value.

Intake Manifold and Carburetor

Edelbrock Performer RPM Intake Manifold

Matching your Edelbrock cylinder heads with a compatible intake manifold is critical for maximizing airflow. The Edelbrock Performer RPM Air-Gap intake manifold (part number 7519) is the premier choice for AMC V8s. Its dual-plane design provides excellent low-end torque while still allowing strong top-end horsepower. The "Air-Gap" design separates the intake runners from the engine heat, keeping the air/fuel mixture cool and dense for more power. The cost for this manifold is typically $350 to $500. For a more budget-conscious build, the standard Edelbrock Performer RPM intake (non-Air-Gap) can be found for $250 to $350, and it will still flow enough for 400 horsepower.

Carburetor Selection

A 400+ horsepower AMC V8 will require a carburetor capable of delivering the necessary fuel. A 750 cfm vacuum secondary carburetor is an excellent choice for a street-driven car. Edelbrock offers the Thunder Series AVS 800 cfm carburetor (part number 1911) which is a perfect match for the Performer RPM intake. This carburetor features an adjustable valve secondary for precise tuning. Expect to pay $300 to $450 for a quality Edelbrock carburetor. If you prefer a Holley, a 750 cfm or 780 cfm vacuum secondary model will also work well and costs approximately $350 to $500.

Fuel System Upgrades

At 400+ horsepower, your stock fuel pump and fuel lines may be inadequate. An Edelbrock mechanical fuel pump (part number 1721) is designed for high-flow applications and costs around $80 to $120. You should also replace the rubber fuel lines with -6 AN braided stainless steel lines and fittings. A fuel line kit from Russell or Earl's will add another $100 to $200. Do not overlook the fuel system; a lean condition caused by fuel starvation will destroy your engine quickly.

Camshaft and Valvetrain

Selecting the Right Camshaft Profile

The camshaft is the brain of the engine, dictating where power is made. For a 400+ horsepower street engine with Edelbrock heads and intake, a camshaft with duration in the 224 to 236 degree range (at 0.050-inch lift) and a lobe separation angle of 110 to 112 degrees will work beautifully. Comp Cams offers the Xtreme Energy (XE) series for AMC V8s. A cam like the XE274H (224/230 duration, .520/.530 lift) is a classic choice that will produce strong power from 2,500 to 6,000 RPM. The cost for a high-performance hydraulic flat tappet camshaft and lifter set ranges from $200 to $400. If you are building a roller cam engine (which is a significant upgrade but requires a substantial investment), expect to pay $600 to $1,200 for the cam and lifters.

Valve Springs, Retainers, and Pushrods

Your Edelbrock heads come with good valve springs, but if you choose a more aggressive camshaft, you may need to upgrade the springs to prevent valve float at high RPM. A set of high-performance valve springs from Crane or Comp Cams will cost $80 to $150. Chrome moly pushrods are also recommended for strength and weight reduction, typically costing $80 to $120. Do not forget the timing chain set (already covered in the short block section) and a new camshaft thrust plate ($15 to $25).

Ignition System: MSD for Reliability and Performance

MSD Ignition Box and Coil

A high-energy ignition system is mandatory for a 400+ horsepower engine. The stock points-type ignition is not capable of firing the air/fuel mixture reliably under high cylinder pressure and high RPM. MSD offers the 6AL-2 Programmable Ignition Control (part number 6425), which provides multiple spark discharge for improved combustion, built-in rev limiter, and timing curve adjustments. The cost for the MSD 6AL-2 box is approximately $300 to $380. You will also need a matching MSD Blaster 2 or Blaster 3 coil, priced around $60 to $90. For a more budget-friendly option, the MSD 6A (non-programmable) can be found for around $200 to $250, and it will still provide excellent performance for a 400 horsepower street engine.

MSD Distributor and Spark Plug Wires

The stock distributor can be used with an MSD ignition box if you install a magnetic pickup conversion kit, but a dedicated MSD billet distributor (part number 8350 for AMC V8) is a much cleaner solution. It features a sealed ball bearing assembly, a CNC-machined billet housing, and a magnetic pickup that works perfectly with the MSD box. Expect to pay $250 to $350 for the distributor. Finally, a set of MSD 8.5mm Super Conductor spark plug wires (around $70 to $100) will handle the voltage without interference and ensure a reliable spark to the plugs. Total MSD ignition system investment: approximately $680 to $920.

Exhaust System: Freeing the Flow

Header Selection

To fully realize the potential of your upgraded engine, you must address the restrictive stock exhaust manifolds. Hooker Headers offers a set of high-quality competition headers for the AMC AMX (part number 6901) that are designed to fit the chassis with power steering and power brakes. These headers typically cost between $500 and $800. If your budget is tighter, you can find generic AMC headers from brands like Pacesetter for $300 to $450. However, the fitment and quality of Hooker headers are generally superior.

Full Exhaust System

A 2.5-inch or 3-inch mandrel-bent exhaust system is required to match the flow capacity of your headers. Flowmaster offers an American Thunder exhaust kit for the AMX (part number 17150) that includes a dual exhaust system with mufflers and tailpipes. This kit typically costs $450 to $700. If you prefer to piece together your own system, expect to spend $250 to $400 on tubing and mufflers (Magnaflow or Flowmaster are excellent choices), plus $100 to $200 for exhaust clamps and hangers. A complete professional exhaust installation will add another $200 to $400 in labor. The total cost for a high-performance exhaust system (headers to tailpipes) is roughly $700 to $1,500.

Cooling System and Supporting Modifications

Radiator and Cooling Fans

400+ horsepower generates significant heat. Your stock radiator will likely struggle to keep the engine cool, especially in summer traffic. An aluminum radiator from Champion or Be Cool designed for the AMX will cost between $250 and $500. An electric fan kit with a thermostat controller adds another $100 to $200. This is a critical reliability upgrade; overheating can cause detonation and engine damage.

Fuel Pump and Pressure Regulator

As mentioned earlier, a high-flow fuel pump is essential. If you choose an electric fuel pump (often easier for street cars), a Holley Blue or Red pump costs $120 to $200, and you will need a fuel pressure regulator ($30 to $60) and return-style fuel line setup. A mechanical pump is simpler and usually sufficient for 400 horsepower. Budget an additional $100 to $250 for the fuel system components.

Total Cost Breakdown Summary

Here is a consolidated estimate of all the major components required to upgrade your AMC AMX to 400+ horsepower using Edelbrock and MSD parts. These are street prices from major retailers like Summit Racing, JEGS, and Edelbrock's own site and do not include labor unless noted.

  • Short Block (Core, Pistons, Rings, Bearings, Oil Pump, Timing Set): $1,080 - $3,990
  • Cylinder Heads (Edelbrock Performer RPM, gaskets, bolts): $1,300 - $1,950
  • Intake Manifold (Edelbrock Performer RPM Air-Gap): $350 - $500
  • Carburetor (Edelbrock 800 cfm AVS): $300 - $450
  • Camshaft and Lifters: $200 - $400
  • Valvetrain (pushrods, springs, retainers): $100 - $270
  • Ignition System (MSD 6AL-2, coil, distributor, wires): $680 - $920
  • Exhaust System (headers, pipes, mufflers): $700 - $1,500
  • Cooling System (aluminum radiator, electric fan): $350 - $700
  • Fuel System (pump, lines, filter, regulator): $200 - $400
  • Gaskets, Seals, Fasteners, Miscellaneous: $150 - $300

Total Estimated Cost: $5,110 to $11,880

This range reflects the significant differences in component choices (e.g., stroker kit vs. stock stroke, Edelbrock heads vs. ported stock heads, programmable MSD vs. basic MSD). A well-planned build targeting 400 horsepower can be achieved in the $7,000 to $9,000 range, including a quality rebuild of the bottom end and the best Edelbrock and MSD parts. If you are starting from a complete, running AMX that only needs a top-end refresh, you could accomplish the goal for as little as $5,500.

Where to Save Money Without Sacrificing Quality

Achieving 400 horsepower does not require the absolute highest-end parts. You can save money by:

  • Using a stock 401 short block: If you have a good 401 with healthy cylinder walls, a basic rebuild with new rings, bearings, and a high-volume oil pump is often sufficient. Skip the stroker kit entirely. This can save $1,000 or more.
  • Choosing a dual-plane intake over an Air-Gap: The standard Edelbrock Performer RPM intake is $100 cheaper and only gives up a few horsepower at the top end.
  • Opting for a non-programmable MSD 6A: The MSD 6A provides excellent spark without the programmable features. It costs about $100 less than the 6AL-2.
  • Installing everything yourself: Professional engine building and installation can add $2,000 to $4,000 in labor. If you have mechanical skills and a decent tool set, this is the single biggest cost savings.
  • Buying components during holiday sales: Summit Racing and JEGS often run sales during Memorial Day, July 4th, and Black Friday. You can save 10-20% on Edelbrock and MSD parts during these events.

Tuning and Professional Engine Balancing

Once all parts are installed, proper tuning is essential. You will need to set the initial timing, adjust the carburetor air/fuel mixture, and dial in the mechanical advance curve in the distributor. An MSD ignition system with adjustable timing curves makes this process easier. If you are not confident in your tuning skills, budget $300 to $600 for a professional dyno tuning session. This will ensure your engine runs optimally, maximizing horsepower and reliability. Additionally, having the rotating assembly (crank, rods, pistons) balanced by a machine shop will cost approximately $200 to $350 and is highly recommended for engine longevity at high RPM.

External Resources for Your Build

Final Thoughts: The Reward Is Worth the Investment

Upgrading your AMC AMX to 400+ horsepower with Edelbrock and MSD parts is a well-defined path that yields tangible results. The transformation from a stock cruiser to a legitimate muscle car that can compete with modern performance is incredibly satisfying. The combination of an Edelbrock top end (heads and intake) with MSD ignition provides a proven foundation that has supported thousands of AMC builds over the years. While the total investment of $5,000 to $12,000 might seem significant, it is important to remember the value of a well-built, reliable 400-horsepower AMX. These cars are appreciating assets, and a properly modified example will always command a premium over a stock, tired original. More importantly, the driving experience—the sound, the torque, the acceleration—will bring a smile to your face every time you get behind the wheel. Plan your build carefully, source your parts from reputable dealers, and do not rush the assembly. Your 400+ horsepower AMX is not just a project; it is a legacy.