Cost vs. Gain: Is a Mopar Performance 318 Conversion Worth It for Your A‑Body?

For Mopar enthusiasts, the A‑body platform—cars like the Plymouth Valiant, Dodge Dart, and early Barracuda—offers a lightweight foundation perfect for performance upgrades. Among the most discussed engine swaps is the Mopar Performance 318 conversion. This small‑block V‑8 is praised for its durability and tractability, but does the financial outlay justify the horsepower and torque gains? In this article we break down every cost, every performance increase, and the intangibles that determine whether a 318 build is the right move for your A‑body.

Understanding the Mopar 318 Engine

The 318 cubic‑inch V‑8 was Chrysler’s workhorse small‑block, produced in various forms from the mid‑1960s through the early 2000s. It was installed in everything from full‑size sedans to police cruisers and pickup trucks, earning a reputation for bulletproof reliability. The LA‑series version (1964–1991) is the most common donor for A‑body swaps, though the later Magnum 318 (1992–2003) offers improved cylinder head flow and a better oiling system.

Key Specifications (LA‑Series 318)

  • Displacement: 318 cubic inches (5.2 L)
  • Bore × Stroke: 3.91 in × 3.31 in
  • Block and Heads: Cast iron (some later Magnum heads were iron as well)
  • Factory Horsepower: 150–250 hp depending on compression ratio, camshaft, and induction system
  • Torque: 260–320 lb‑ft at low rpm
  • Valvetrain: Overhead valve (pushrod) with two valves per cylinder

What makes the 318 attractive for an A‑body swap is its compact external dimensions. It fits between the frame rails of early A‑bodies without major firewall modifications, and it weighs roughly 100 pounds less than a big‑block, helping maintain good front‑to‑rear weight balance.

The A‑Body Platform: Why It Matters

A‑bodies are Chrysler’s compact cars built from 1960 to 1976. They include the Dodge Dart, Plymouth Valiant, early Duster, and the first‑generation Barracuda. These cars are lighter than B‑bodies (Charger, Coronet) and E‑bodies (Challenger, ‘Cuda), making them nimble and responsive to modest power increases. A 300‑hp 318 in a 3,000‑lb Dart delivers a power‑to‑weight ratio that few cars from the era could match, yet the swap can be completed with hand tools and a weekend of work.

Complete Cost Breakdown of a Mopar Performance 318 Conversion

Every build is different, but a realistic budget for a turnkey conversion—one that starts with a stock or rebuilt 318 and includes all necessary supporting parts—falls between $4,500 and $9,000. Below is a line‑by‑line estimate based on current aftermarket pricing and average machine shop labor.

Donor Engine and Rebuild Costs

  • Used core engine (LA‑series): $200–$600
  • Rebuilt short‑block from a reputable shop: $1,500–$3,000
  • Complete rebuilt long‑block (with heads, cam, intake): $3,500–$5,000
  • Mopar Performance crate engine (318 Premium): $4,200–$5,500

Installation Labor

  • DIY (your own time): $0, but expect 20–40 hours
  • Professional shop (simple swap): $800–$1,500
  • Professional shop (full conversion including wiring and mounts): $1,500–$2,500

Supporting Parts & Performance Upgrades

  • Headers: $250–$600 (must be A‑body specific for steering shaft clearance)
  • Exhaust system (dual 2.25–2.5 in): $300–$800
  • Intake manifold (e.g., Edelbrock Performer or Air‑Gap): $200–$400
  • Carburetor (if not fuel injection): $300–$600
  • Ignition system (MSD or HEI conversion): $150–$400
  • Radiator (3‑row copper or aluminum): $200–$500
  • Engine mounts & adapter brackets: $100–$250
  • Transmission (rebuild or upgrade, if needed): $500–$1,200
  • Fuel system (electric pump, lines, regulator): $150–$400

Miscellaneous & Consumables

  • Gaskets, seals, fluids, filters: $100–$250
  • Wiring harness modifications or new engine harness: $100–$300
  • Hoses, belts, clamps: $50–$150
  • Unexpected machine work (line bore, deck resurface): $200–$500

If you choose a Mopar Performance crate engine (the 300‑hp or 340‑hp versions), you eliminate many rebuild variables but pay a premium. Given the costs above, the total can climb quickly, but careful sourcing of used parts and doing the labor yourself can keep the project under $4,500.

Performance Gains: What the 318 Actually Delivers

A stock 1960s 318 with a two‑barrel carburetor and restrictive exhaust might grind out 175 hp at the flywheel. After a conversion using a Mopar Performance cam, four‑barrel intake, headers, and a mild cylinder head port job, the same engine can produce 285–325 hp and 340–380 lb‑ft of torque. That’s a jump of 100–150 hp, transforming an A‑body from a lethargic cruiser into a street‑light dominator.

Real‑World Dyno Results

A popular spec for a budget 318 build is: 9.2:1 compression, a Hughes Engines HE1120 cam (214/224 at 0.050), an Edelbrock Performer intake, a 650‑cfm Holley, and 1-5/8 in headers. On a chassis dyno, A‑bodies with this combination have posted 250–270 rear‑wheel horsepower, equating to roughly 300–320 at the crankshaft. Torque peaks at about 3,200 rpm, giving the car strong mid‑range pull without needing to rev to the moon.

Torque Characteristics

Unlike a high‑winding 340 or 360, the 318’s longer stroke (relative to bore) favors low‑end torque. That makes it ideal for daily driving and stop‑and‑go traffic. With a manual transmission, you can launch hard on street tires without spinning excessively. The engine also tolerates mild rear gears (3.23:1 or 3.55:1) well, letting the engine rev efficiently on the highway.

Compare: 318 vs. 340 vs. 360 as Potential Swaps

Many A‑body builders wonder if the extra cubes of a 340 or 360 are worth the added expense. Here’s how they stack up in a conversion context:

Engine Displacement Cost (rebuilt long‑block) Peak HP (mild build) Weight Difference Fitment Ease
318 LA 318 ci $3,000–$4,500 300–325 hp Baseline Easiest – minimal firewall mods
340 340 ci $4,500–$7,000 350–400 hp ~15 lbs more Good – same block dimensions
360 360 ci $3,500–$5,500 350–380 hp ~20 lbs more Requires checks (steering, headers)

The 318’s key advantage is cost and ease of fit. The 360 can be had cheaply (many truck versions), but its taller deck height may need special headers or minor firewall adjustment in early A‑bodies. The 340 is the rarest and most expensive, often costing more per horsepower than a 318 with aftermarket aluminum heads. For a street‑driven A‑body that seldom sees 6,000 rpm, the 318 provides the best balance of dollars and drivability.

Installation Considerations and Common Pitfalls

Engine Mounts and K‑Member

Early A‑bodies (1960‑1966) use a different K‑member than later models. If your car originally came with a slant‑six, you will need V‑8 K‑member or adapter mounts. Aftermarket conversion mounts from firms like Schumacher Creative Services or MA Performance simplify the swap. For 1967‑1976 A‑bodies, factory V‑8 K‑members accept the 318 directly, but verify that your engine mount brackets are the correct width.

Transmission Compatibility

The 318 bolts to any Chrysler small‑block bellhousing pattern. Common pairings include the three‑speed A833 manual or the 904/727 TorqueFlite. If your donor 318 came from a truck, it may have a different flexplate or flywheel balancing (external vs. internal). Always check the crankshaft flange style and balance. Most aftermarket converters and clutches require a zero‑balance or neutral‑balance damper.

Wiring and Electronics

Swapping from a slant‑six: you must adapt the charging system and starter wiring. The 318 uses a different starter mounting and may need a mini‑starter to clear headers. The factory ammeter wiring should be upgraded to handle the increased load from a higher‑output alternator (recommend 70‑100 amp). Use a dedicated engine harness from Painless Performance or Ron Francis Wiring to avoid gremlins.

Cooling System

A V‑8 generates more heat than a six. Upgrade to a three‑row copper radiator or an aluminum cross‑flow unit. A 180‑degree thermostat and a seven‑blade fan clutch combo keep temperatures stable even in summer traffic. Avoid using an electric fan unless you have a high‑output alternator and a proper shroud.

Header Clearance

318 engines sit lower in the chassis than a big block, but header clearance on the driver’s side can be tight with power steering. Shorty headers (like those from Hooker or Hedman) often clear the steering box; full‑length headers may require a steering box modification or manual steering conversion. Test fit before final installation.

Factors to Consider Before You Decide

Your Budget – The Hidden Costs

Many builders focus on the engine cost and forget about ancillary items: new motor mounts, transmission rebuild, driveshaft shortening, cooling system, exhaust, and gauges. Set aside a 15% contingency fund for unexpected machining or parts. If you cannot stomach a $9,000 project, a mild 318 build with a used engine and minimal upgrades can be done for $4,000–$5,000, but you’ll compromise on peak power.

Intended Use – Daily Driver vs. Weekend Warrior

A 318 with a mild cam and iron intake makes excellent low‑end torque and cruises quietly with dual exhaust. It’s perfect for a daily driver. For track days or autocross, a 340 or 360 with aluminum heads might offer more headroom, but the 318 can still be built to 400 hp with a stroker kit (using a 360 crank). Be honest about how you’ll use the car: the 318 conversion is rarely disappointing for street use.

Future Modifications – Building a Foundation

If you plan to add a supercharger or nitrous later, start with a 318 block that has four‑bolt main caps (rare but available from later Magnum engines) or install a main cap stud girdle. The LA block’s webbing is strong enough for 500–550 hp with proper fasteners. Also consider that future upgrades like aftermarket heads (Edelbrock E‑Streets or ProMaxx) can be added later to a 318 to push power past 400 hp without swapping blocks.

Resale Value – How the Market Sees a 318 Swap

Among Mopar purists, a 340‑ or 360‑powered A‑body typically commands a higher price than a 318 car, but the difference may be smaller than the cost of the swap. If you are building the car for yourself and plan to keep it long term, resale value is less important. For a flipper, a documented 318 crate engine swap can still attract buyers who value reliability and low‑cost motoring.

Real‑World Cost vs. Gain Analysis

Let’s put numbers to paper. A budget‑minded swap using a used 318 core ($400), a basic rebuild kit ($350), a mild cam ($150), a used four‑barrel intake ($100), used headers ($200), and a rebuilt carb ($200) adds up to about $1,400 in parts, plus your own labor. That 1,400‑pound investment yields a 100–120 hp gain over the stock slant‑six. That’s about $12–$14 per horsepower—an outstanding value in the performance world.

On the other end, a full turnkey build with a Mopar Performance crate 318, professional installation, and premium components can top $9,000 for 320 hp, or about $28 per horsepower. That’s still competitive with modern crate engine packages, and you retain the original “numbers matching” vibe if you keep the original engine aside.

By comparison, a 340 swap often costs $7,000–$10,000 for a comparable 350‑hp build (higher core cost, rare parts). The 318 gives you 80–90% of the performance at 60–70% of the cost.

Conclusion

The Mopar Performance 318 conversion is one of the most cost‑effective ways to wake up a sleepy Mopar A‑body. It offers a substantial power increase, excellent durability, and a massive aftermarket support network. The engine fits with minimal modifications, parts are still inexpensive, and the torque curve is tailor‑made for street driving. Whether you are building a driver, a weekend cruiser, or a bracket‑racing sleeper, the 318 swap delivers real results without breaking the bank.

If you are on the fence, start by sourcing a solid LA‑series or Magnum 318 core. Spend your money on a quality cam, a good cylinder head port job (or aftermarket heads), and a well‑matched carburetor. Skip cosmetic frills. The result will be an A‑body that not only performs better but also rewards you with that unmistakable small‑block Mopar sound.

For further reading and parts sourcing, consult community resources like For A Bodies Only, Mopar Action, and the technical articles at Allpar. These sites offer dyno tested builds and feedback from thousands of A‑body owners who have already made the 318 leap.