Understanding the Mopar Performance 340 Intake Manifold

The Mopar Performance 340 intake manifold is a high-performance replacement designed specifically for Chrysler’s iconic 340 cubic-inch small-block V8 engine. Originally introduced in the late 1960s, the 340 became legendary for its strong power output and lightweight design. This aftermarket manifold improves airflow into the cylinders, allowing the engine to breathe more efficiently at higher RPMs, which translates into increased horsepower and torque. Whether you’re restoring a classic Dodge Dart Swinger, Plymouth Duster, or building a street/strip machine, this upgrade is a proven path to waking up the small-block’s potential. The manifold is cast from aluminum for weight savings and features a dual-plane design that balances low-end torque with top-end power, making it suitable for both street driving and occasional track use. Before diving into installation, it’s important to understand how this part integrates with your engine’s existing systems, including the fuel delivery, ignition, and cooling circuits. This guide assumes you have a basic familiarity with engine mechanics and the right workspace.

Tools and Materials Needed

Having the correct tools and materials on hand will save you time and prevent mid-job frustration. The following list covers everything you’ll need for a smooth installation:

  • Socket set (metric and SAE, with extensions and a universal joint for awkward angles)
  • Torque wrench (able to measure in foot-pounds; a 3/8-inch drive is usually sufficient)
  • Gasket scraper (plastic or brass to avoid gouging aluminum surfaces)
  • New intake manifold gasket set (OEM or Fel-Pro quality; do not reuse old gaskets)
  • Thread locker (medium-strength, e.g., Loctite 242) for bolt threads
  • Engine oil (to lightly lubricate gasket surfaces and bolt threads)
  • Rags and shop towels for cleanup
  • Safety glasses and mechanic’s gloves
  • Shop vacuum with a small nozzle (to remove debris from open intake ports)
  • Gasket sealer (optional, for water jacket ports if recommended by your gasket manufacturer)
  • Marker or labeling tape for hoses and wires

You may also need a lift or jack stands if working on a vehicle with limited engine bay access. A helper can be useful for carefully positioning the manifold.

Preparation Steps

Proper preparation is the foundation of a successful intake manifold swap. Rushing this phase often leads to leaks, stripped threads, or misaligned parts.

Engine Cooling and Safety

Ensure the engine has been off and completely cool to the touch—at least two hours after the last run. Hot engine components can cause severe burns. Disconnect the negative battery terminal to prevent any electrical sparks or accidental starter engagement while you work.

Access and Clearance

Remove any components that block access to the intake manifold. This typically includes the air cleaner assembly, throttle body or carburetor, fuel lines, distributor cap (if distributor is mounted in the intake), and any wiring harnesses routed over the manifold. For vehicles with emission control systems, you may also need to detach the EGR valve, PCV valve and hoses, and vacuum lines. Take photos or label each connection with tape and a marker before disconnecting. This will save enormous time during reassembly. Use a socket to remove the distributor hold-down bolt and gently lift the distributor, noting its rotor position—you can turn the engine over if needed, but it’s easier to mark the housing for reinstallation.

Drain Coolant (If Necessary)

Many 340 intake manifolds incorporate coolant passages below the carburetor flange. If yours has these, you will need to drain the cooling system below the level of the manifold. Place a drain pan under the radiator petcock and open it. You can also loosen the lower radiator hose to drain the block. This step prevents coolant from spilling into the valley when the manifold is removed.

Removing the Old Intake Manifold

With the engine cool and accessories cleared, it’s time to lift the old manifold. Work carefully to avoid dropping debris into the engine.

Remove Bolts and Hardware

Using a socket and ratchet, remove all intake manifold bolts. There are usually 12 to 16 bolts of varying lengths arranged around the perimeter. Keep them organized by location; a piece of cardboard with holes punched in the pattern works well. Some bolts may have a different head size or thread pitch, especially those at the front and rear. If a bolt is stubborn, apply penetrating oil and let it soak for a few minutes. Do not force it, as snapping a bolt in the block is a major setback.

Break the Gasket Seal

Once all bolts are removed, gently tap the manifold with a rubber mallet or use a pry bar at the cast-in prying bosses. Never pry against the block or cylinder head surfaces, as this can damage the mating surfaces and cause leaks. If the manifold does not lift free, recheck for hidden brackets or ground straps that may still be attached.

Lift and Inspect

Carefully lift the manifold straight up. It may be heavy (around 25–35 pounds), so support it with both hands. Place it on a clean work surface. Now inspect the old gasket and the engine’s intake ports and valley. Use a gasket scraper to remove all traces of the old gasket material from the cylinder head and block deck. Be thorough but gentle to avoid gouging the aluminum surfaces of the heads. Wipe the area with a clean rag lightly dampened with brake cleaner. Finally, use a shop vacuum with a narrow attachment to suck out any small bits of gasket or debris that may have fallen into the lifter valley or open ports.

Installing the New Mopar Performance 340 Intake Manifold

This is the heart of the project. Taking your time at this stage ensures a leak-free seal and optimal performance.

Gasket Preparation and Placement

Use a high-quality gasket set designed for the 340 small-block. Apply a thin, even coat of engine oil (or the gasket manufacturer’s recommended sealer) to both sides of the gasket where it contacts the block and manifold. Some builders also use a small dab of high-temp silicone at the four corners where the gaskets meet the china walls (the front and rear sealing surfaces). Place the gaskets carefully onto the block, aligning them with the intake ports and water passages. Do not let the gaskets shift during manifold placement.

Lower the Manifold

Before placing the manifold, apply a thin layer of engine oil to the bolt threads to ensure accurate torque readings and prevent galling. Lift the new Mopar Performance manifold and lower it straight down, aligning the dowel pins or alignment sleeves if present. The manifold should sit flush on the gaskets without rocking. Do not slide it sideways after contact, as this can disturb the gasket.

Install Bolts and Torque Sequence

Insert all bolts finger-tight. The factory torque sequence typically starts from the center and works outward in a cross pattern. Refer to the service manual for your specific engine, but a common specification for small-block Chrysler intake manifolds is 30–35 ft-lbs for 3/8-inch bolts, and 20–25 ft-lbs for smaller bolts. Always use a torque wrench; overtightening can crack the manifold or distort the gasket. Tighten in three steps: first to 15 ft-lbs in sequence, then to 25 ft-lbs, and finally to the full specification. After the final torque pass, recheck each bolt one more time in sequence.

Reconnecting Components

With the manifold securely in place, you can reassemble all the parts you removed earlier. Pay close attention to routing and sealing.

Ignition and Fuel System

If a distributor was removed, reinstall it with the rotor pointing toward the same #1 terminal mark you observed during disassembly. You may need to rotate the oil pump drive shaft with a long flathead screwdriver to seat the distributor fully. Reattach the distributor cap and spark plug wires in the correct firing order (1-8-4-3-6-5-7-2 for most 340 engines). Connect the fuel line to the carburetor or throttle body using new O-rings if applicable. For carbureted setups, replace the fuel filter at this time.

Cooling, Vacuum, and Electrical

Reconnect all coolant hoses, making sure the heater hose ports on the manifold align. Fill the cooling system with the appropriate mixture of antifreeze and water. Attach vacuum lines to the correct ports—you can use a vacuum diagram from a service manual or your labeled photos. Secure the throttle linkage or accelerator cable, and reconnect any wiring harness retainers. Before moving on, double-check that no tools or rags are left in the engine bay.

Final Steps

Now comes the critical verification phase. Rushing these checks can undo all your careful work.

Battery and Initial Start

Reconnect the negative battery terminal. Prime the engine by cranking it with the ignition disabled (pull the coil wire or disable the fuel pump) for about 10 seconds to build oil pressure. Then allow the fuel pump to fill the carburetor or prime the injection system. Start the engine and let it idle. Immediately listen for any vacuum leaks (a hissing sound) and inspect the manifold gasket edges for signs of fuel or coolant leaking. If you see a leak, shut down the engine and retorque the bolts at that area (if safe), or replace the gasket if necessary.

Temperature Cycle and Retorque

Allow the engine to reach normal operating temperature (typically 190°F–210°F). Then shut it off and let it cool completely. During this first heat cycle, the gaskets compress and the bolts may relax. After the engine is cool, perform a final retorque of the intake manifold bolts to the same specification, following the sequence again. This step is often overlooked but crucial for long-term sealing. Check coolant level and top off as needed.

Test Drive and Fine-Tuning

Take the vehicle for a test drive of at least 15–20 minutes, including a mix of low-speed and moderate acceleration. Listen for any unusual noises and watch the temperature gauge. After returning home, inspect the manifold area again for any seepage. If all is well, you can button up any remaining trim or heat shields. It’s also a good time to set your ignition timing and adjust the carburetor air/fuel mixture if necessary, as the improved airflow may require slight tuning.

Common Mistakes to Avoid

Even experienced mechanics can fall into these traps. Being aware of them will save you frustration:

  • Using excessive gasket sealer – Too much RTV can squeeze out into oil passages or coolant ports, causing clogs. A thin bead at the china walls is sufficient; let gaskets do the work.
  • Cross-threading bolts – Always start bolts by hand. If resistance is felt immediately, remove and check alignment.
  • Ignoring the torque sequence – Tightening in random order can warp the manifold or create a gap.
  • Skipping the retorque – Gaskets compress after heat cycles, so the retorque is essential.
  • Not labeling components – Trust us, you won’t remember which vacuum line went where three days later.

Performance Tuning After Installation

The Mopar Performance 340 intake manifold is designed to work best with a matching camshaft, headers, and a free-flowing exhaust. If your engine is otherwise stock, you will still see a moderate gain, but to fully realize its potential, consider upgrading the following:

  • Carburetor or throttle body – A 750 cfm Holley or Edelbrock carburetor is a popular match.
  • Ignition system – An MSD electronic distributor and coil will provide a hotter spark.
  • Exhaust system – Long-tube headers and a low-restriction exhaust system help the engine breathe out.

After any such changes, a professional dyno tuning session is the best way to dial in the air/fuel ratios and ignition timing for maximum safe power.

Additional Resources

For more technical specifications and genuine parts, visit the official Mopar Performance website. Community forums such as For A Bodies Only provide real-world installation tips and troubleshooting advice from owners who have completed this exact swap. For detailed torque specs and engine diagrams, consult the Factory Chrysler Parts catalog or the 340 engine service manual. Finally, if you need a high-quality replacement gasket set, brands like Fel-Pro offer specific kits for the 340 intake manifold that are trusted by professionals.

Conclusion

Installing the Mopar Performance 340 intake manifold is one of the most rewarding upgrades you can perform on your classic Chrysler small-block. It delivers a noticeable improvement in throttle response and upper-RPM power while remaining streetable. By following this expanded guide, paying close attention to cleanliness, torque procedures, and component labeling, you’ll achieve a leak-free installation that performs reliably for thousands of miles. Whether you’re building a show car, a weekend cruiser, or a bracket racer, this manifold lays the foundation for serious horsepower. Take your time, use the right tools, and enjoy the transformation.