Overview of the Mopar 340 Engine

Introduced in 1968, the Mopar 340 is one of Chrysler’s most iconic small-block engines. It was designed as a high-performance powerplant for the muscle car era, finding its way into classics like the Plymouth Barracuda, Dodge Challenger, and Dodge Charger. With a 4.04-inch bore and 3.31-inch stroke, the 340 displaced 340 cubic inches and came with a factory rating of 275 to 340 horsepower depending on the year and configuration. Today, the 340 remains a favorite among enthusiasts because of its excellent power-to-weight ratio, durable bottom end, and broad aftermarket support. Building a Mopar 340 with forged pistons, a performance camshaft, and a free-flowing exhaust system can push output well beyond 400 horsepower while keeping the engine reliable. This article provides a detailed cost breakdown for each major component, helping you plan a build that fits your budget and performance goals.

Performance Pistons – The Foundation for Compression and Durability

The piston assembly directly affects compression ratio, strength, and thermal management. Factory 340 pistons were cast units with low compression (8.5:1 to 10.5:1 depending on year). For a performance build, upgrading to forged or hypereutectic pistons is a must if you plan to use forced induction, nitrous, or high-rpm operation.

Types of Performance Pistons for the Mopar 340

  • Forged Pistons: Strongest option, ideal for boosted or high-rpm applications. Brands include Mahle, CP-Carrillo, JE, and Diamond. A set of four (8 pistons for a V8) typically runs $600–$1,200.
  • Hypereutectic Pistons: Cast with high silicon content, offering better heat resistance than standard cast. Good for street builds with moderate power goals. Cost: $400–$700 a set.
  • Standard Cast Pistons: Suitable for low-cost rebuilds with near-stock power. Often <$400 a set, but not recommended for 450+ hp.
  • Piston Rings: Must match the cylinder wall finish and ring groove. Forged pistons often require moly or stainless steel rings. Set cost: $80–$200.
  • Wrist Pins & Retainers: Often included with pistons, but if not, budget $30–$80.
  • Balancing: Aftermarket pistons often require reciprocating assembly balancing. Machine shop charge: $150–$350.

Example build choice: For a 400-hp street motor with occasional strip use, a set of Icon forged pistons (around $700) plus Total Seal rings ($120) offers excellent value. For a 500+ hp blown application, spend $1,100 on a set of CP-Carrillo pistons and $160 on custom rings. Browse current piston options for the 340 at Summit Racing.

Camshaft – Shaping the Power Curve

The camshaft controls valve timing, lift, and duration, which determine where the engine makes peak power and torque. The 340 responds well to aftermarket cams, with hydraulic flat tappet and roller designs being the most common. A cam swap is one of the best ways to wake up a 340 without spending a fortune.

Camshaft Types for the Mopar 340

  • Hydraulic Flat Tappet: Budget-friendly, well-suited for mild street builds (250–400 hp). Cam alone: $200–$400. Requires break-in procedure with dedicated oil. Brands: Comp Cams, Lunati, Mopar Performance.
  • Hydraulic Roller: Lower friction, more aggressive profiles, better stability at higher rpm. Cam alone: $500–$1,000. Requires roller lifters (extra $300–$500) and sometimes a different timing chain set. Great for 400–550 hp builds.
  • Solid Flat Tappet / Solid Roller: For race-only applications; solid lifters require periodic lash adjustment. Solid roller cams can exceed $1,200 with lifters.

Included in a Cam Kit

Most camshafts require a matched kit: cam, lifters, timing chain set, and sometimes valve springs. A complete hydraulic roller kit (cam + lifters + chain) runs $700–$1,400. Budget an extra $200–$400 for upgrade valve springs and retainers if the cam lift exceeds 0.500.

Picking the Right Profile

  • Street/strip 300–350 hp: 212°–224° duration at 0.050, 0.450–0.480 lift, LSA around 110–112.
  • Stout 400–450 hp: 230°–240° duration, 0.500–0.540 lift, LSA 108–110.
  • Race 500+ hp: 250°+ duration, 0.600+ lift, solid roller setup.

Cost-saving tip: If you’re on a tight budget, a single-pattern hydraulic flat tappet cam from Mopar Performance (PN P4452039) costs about $220 and works well with stock heads and intake. Hughes Engines offers custom cam grinding and kits for Mopar 340s.

Exhaust System – Freeing the Flow

The 340’s stock exhaust manifolds are restrictive. Upgrading to headers and a larger-diameter exhaust system can unlock 20–40 hp on a mild build and even more on high-output setups. The exhaust cost depends on material (mild steel vs. stainless), header style (shorty vs. full-length), and the rest of the system (X-pipe, mufflers, tips).

Headers

  • Shorty headers: Easier installation, fit most A- and E-body chassis, good for 300–380 hp. Cost: $300–$600 (mild steel coated).
  • Full-length long-tube headers: Best for power over 4,000 rpm, clearance may be tight. Cost: $500–$900 (painted or ceramic coated). Brands: Hooker, TTI, Doug’s Headers.
  • Stainless steel headers: Corrosion resistant, ideal for street cars driven in all weather. Cost: $800–$1,400.

Cat-Back Exhaust System

  • 2.5-inch mandrel-bent system: Good for up to 400 hp. Cost: $400–$700.
  • 3.0-inch system: Needed for 450+ hp builds. Cost: $600–$1,200.
  • Aluminized vs. stainless: Aluminized costs 30–50% less but will rust over time. Stainless is permanent.

Mufflers and Hardware

  • Performance mufflers (e.g., Flowmaster, MagnaFlow): $100–$200 each (two required).
  • H-pipe or X-pipe crossover: $100–$250 (often included in full exhaust kits).
  • Exhaust tips, clamps, hangers: $100–$300.

Real-world example: A TTI long-tube header set for a 1970 Challenger costs about $850, and a MagnaFlow 2.5-inch cat-back system adds $650. That’s $1,500 for the full exhaust, not including installation. Consider TTI headers for exact fitment on Mopar chassis.

Additional Costs – The Details That Add Up

Beyond pistons, cam, and exhaust, overlooked expenses can blow your budget. Here’s a comprehensive list:

  • Machine Work: Cylinder boring/honing ($200–$500), resurfacing heads and block ($150–$300), line honing main bearings ($200–$400), balancing rotating assembly ($150–$350). Total: $700–$1,500.
  • Gaskets and Seals: Complete gasket set (Fel-Pro or Victor Reinz) $150–$300. Head gaskets alone $50–$120 for performance versions.
  • Timing Set: Roller timing chain set with camshaft: $80–$200.
  • Oil Pump: Melling high-volume oil pump: $80–$150. Pickup tube and screen: $30–$60.
  • Valve Train: If you change cam, often you need new pushrods ($60–$120), rocker arms (optional upgrade to roller rockers: $300–$600), valve springs ($100–$200).
  • Carburetor & Intake Manifold: For a street 340, an Edelbrock Performer RPM intake ($250–$400) and a 650–750 cfm carburetor ($300–$600) are common upgrades. Not included in this article’s scope but often done simultaneously.
  • Labor (if not DIY): Full assembly by a competent shop: $1,500–$3,000. Short-block assembly: $800–$1,500. Head rebuild: $400–$800.
  • Miscellaneous: Bolts, thread sealant, fluids, plugs, wires, coolant – budget $200–$400.

Total Estimated Build Cost – Three Tiers

Based on the components discussed, here are realistic total costs for a Mopar 340 build with forged pistons, performance cam, and upgraded exhaust. These figures assume you do the assembly yourself except for machine work.

Build Tier Projected Power Component + Machine Cost Total (incl. cam & exhaust)
Budget Street 320–340 hp Cast pistons ($300) + hydraulic flat tappet cam ($220) + shorty headers & 2.5" exhaust ($700) + machine work ($800) + misc ($300) = $2,320 $2,500–$3,000
Solid Street/Strip 380–430 hp Forged pistons ($700) + hydraulic roller cam kit ($800) + long-tube headers & 3" exhaust ($1,200) + machine work ($1,200) + misc ($500) = $4,400 $4,000–$5,500
High-Performance / Race 480–550 hp Custom forged pistons ($1,100) + solid roller cam kit ($1,400) + stainless headers & 3" exhaust ($1,600) + machine work & balancing ($2,000) + misc ($700) = $6,800 $6,500–$9,000+

Note: These totals do not include the cost of a new intake, carburetor, ignition system, or forced induction. If you need a complete build from long-block to running engine, add $1,500–$3,000 for those subsystems.

Making Sense of the Numbers

When budgeting your 340 build, prioritize components that give the best bang for the buck. The camshaft and exhaust usually offer the largest horsepower per dollar spent. Pistons are a necessary upgrade if you want to raise compression or handle boost, but you can reuse factory rods and crank if they pass inspection. Machine work quality cannot be skimped – a poorly honed cylinder or imbalanced assembly will destroy the engine quickly. Shop around for quotes from reputable engine builders. Mancini Racing is a solid source for Mopar-specific internal engine parts and machine services.

Conclusion

Building a Mopar 340 with forged pistons, a performance cam, and a free-flowing exhaust is a proven recipe for reliable, exciting power. Depending on your goals and willingness to turn wrenches, you can spend anywhere from $2,500 to $10,000. The key is to choose components that match your intended use – a daily-driven street machine benefits from a mild cam and 3-inch exhaust, while a weekend bracket racer needs the strongest reciprocating assembly you can afford. With the cost breakdown above, you can now plan a build that keeps your budget on track while delivering the legendary Mopar performance that makes the 340 a favorite worldwide.