The 340 Engine – A Legend in Mopar History

Before diving into the intake and carb swap, it helps to understand the foundation. Chrysler’s 340 cubic inch V8, introduced in 1968, was a small-block powerhouse built for high-RPM performance. With a forged steel crank, heavy-duty rods, and free-breathing cylinder heads, the 340 became the go-to engine for mid-size B-bodies like the Dodge Charger, Coronet, Plymouth Satellite, and GTX. While factory-rated at 275 to 290 horsepower depending on the year, the 340 had plenty of untapped potential—especially when you freed up its restrictive intake and carburetion.

The Mopar Performance 340 Hopper intake manifold is a direct descendant of the factory “Torker”-style manifolds, but with significantly better airflow characteristics. When paired with a correctly sized carburetor, this swap consistently delivers a real-world gain of 30–35 horsepower at the rear wheels. For many B-body owners, that’s the difference between a cruiser that’s fun to drive and a street machine that demands respect.

Anatomy of the Mopar Performance 340 Hopper Intake

The term “Hopper” refers to the distinct plenum design that funnels air into each runner with minimal turbulence. Unlike the factory cast-iron or even the later spread-bore aluminum manifolds, the Mopar Performance 340 Hopper intake uses a dual-plane layout optimized for the 340’s 302° (or similar) camshafts and high-flow cylinder heads. Key features include:

  • Wider plenum volume – Allows better air/fuel mixture distribution across all eight cylinders.
  • Divided plenum runners – Maintains velocity at low RPM for solid street manners, then opens up at high RPM for top-end power.
  • Lightweight aluminum construction – Saves about 20 pounds off the nose compared to cast-iron manifolds, improving weight distribution and handling.
  • Standard 4150 square-bore flange – Accepts most popular aftermarket carburetors without adapters.

This intake was originally sold through Mopar Performance (now rebranded as Direct Connection) and remains a favorite among restorers and street rodders because it looks period-correct while delivering modern airflow numbers. According to Summit Racing, flow bench tests show a 25% improvement in air capacity over the stock 340 four-barrel intake, particularly in the secondary side.

Why It’s Called the “Hopper”

The nickname “Hopper” comes from the internal shape of the plenum floor, which rises steeply from the front to the rear. This design helps “funnel” or hop the incoming fuel mixture toward the rear runners, preventing fuel puddling during hard acceleration. It’s a clever bit of engineering that Chrysler’s performance division perfected in the late 1960s.

Selecting the Right Carburetor

Even the best intake manifold is only as good as the carburetor sitting on top of it. The stock 340 Carter AVS or Thermo-Quad can work, but their small venturii limit horsepower above 5,000 rpm. For the full 35 HP gain, you need a carburetor that matches the Hopper’s flow potential.

Here are the critical factors to consider:

  • CFM rating – For a 340 that sees 6,000+ rpm, 650 to 750 CFM is the sweet spot. A 650 CFM will give crisp throttle response; a 750 CFM will unlock the top-end horsepower but requires careful tuning to avoid bogging.
  • Vacuum secondary vs. mechanical secondary – Vacuum secondaries (e.g., Holley 3310) are forgiving for street use. Mechanical secondaries (e.g., Holley Double Pumper) deliver instant power and are preferred for drag racing.
  • Spacer or no spacer? – A 1-inch open spacer under the carburetor can improve mid-range torque by another 5–8 lb-ft, but check hood clearance first.

Top Carburetor Recommendations for the 340 Hopper

1. Edelbrock Performer Series (600–750 CFM)

These are modern versions of the Carter AFB. They are easy to tune, have no power valve to blow, and offer excellent street drivability. For a near-stock 340, the 650 CFM (model 1406) is a simple bolt-on. For a mild cam, go with the 750 CFM (model 1411).

2. Holley 750 CFM Double Pumper (model 4779)

This is the classic choice for the 340 Hopper. With mechanical secondaries and four-corner idle adjustment, it provided the 35 HP gain that many magazine tests have documented. The accelerator pump circuit delivers a big shot of fuel the instant you nail the throttle, which is exactly what the 340’s cam overlap demands.

3. Quick Fuel Technology Q-Series (750 CFM)

A modern evolution of the Holley design with billet metering blocks, stainless steel floats, and a smoother baseplate. It flows about 30 CFM more than a standard Holley of the same rating, which translates directly to horsepower. Many racers use the Q-750 with a 340 Hopper on 9.5:1 compression motors and see over 400 HP at the crank.

For more detailed carburetor specs, check out Mopar Action’s tech articles, which frequently test these combinations on dynos.

Installation Step-by-Step

Swapping an intake and carburetor on a B-body 340 is a weekend project for anyone with basic mechanical skills. Plan for 6–8 hours of work, plus tuning time. Below is a comprehensive guide.

Tools & Supplies Needed

  • 1/2” and 3/8” socket sets, torque wrench (ft-lbs and in-lbs)
  • Carburetor gasket set (for 340 Hopper intake – part number P2733849 or equivalent)
  • RTV silicone gasket maker (intake end seals)
  • Carburetor studs and nuts (3/8” thread for 340 Hopper)
  • Fuel line with correct fittings (3/8” supply, 5/16” return)
  • Carburetor linkage bracket adapter

Removal

  1. Disconnect the battery negative terminal.
  2. Remove the air cleaner, then disconnect the throttle, transmission kickdown, and vacuum lines from the carburetor.
  3. Disconnect the fuel line using a line wrench to avoid rounding.
  4. Unbolt the carburetor and set it aside.
  5. Remove the intake bolts in reverse torque sequence. Carefully lift the old intake – use a helper to avoid damaging the heads.
  6. Clean the block deck and lifter valley thoroughly. Scrape old gasket material with a plastic scraper. Use brake cleaner and compressed air to remove debris.

Installation

  1. Apply a 1/8” bead of RTV to both ends of the block (the “China walls”). Install the intake gaskets – use the thicker/cork type for better sealing on iron heads.
  2. Lower the 340 Hopper intake onto the engine. Be careful not to dislodge the gaskets. Hand-thread all intake bolts, then torque in three steps using the factory sequence: first to 25 ft-lbs, then 35 ft-lbs, and final to 45 ft-lbs (or as specified by Mopar – never exceed 50 ft-lbs on aluminum intakes).
  3. Reattach the carburetor with a new gasket. Tighten nuts to 90 in-lbs (alternating crisscross).
  4. Connect the fuel line with new compression ferrules. Use thread tape on fittings to prevent leaks.
  5. Reinstall throttle linkage and kickdown cable. You may need a carburetor linkage bracket kit (available from Mopar Performance) to align the geometry correctly.
  6. Attach vacuum lines (distributor advance, PCV, brake booster).
  7. Reconnect battery, check for any loose wires or air cleaner clearance, then start the engine.

Initial Startup and Leak Check

With a fire extinguisher nearby, crank the engine. If it starts, let it idle at 1200–1500 rpm for the first 30 seconds to circulate coolant. Immediately check for coolant or fuel leaks. If no leaks, allow the engine to warm until the thermostat opens. Then set initial idle speed to about 800 rpm and adjust mixture screws (typically 1.5 turns out from seated on Holley carbs).

Tuning for Maximum Power

The 35 HP gain is not automatic – you need to dial in the carburetion and ignition timing. Here’s what separates the pros from the posers.

Idle Mixture and Throttle Response

Use a vacuum gauge. Connect it to a manifold vacuum source (full vacuum, not ported). Adjust the idle mixture screws on the carburetor to achieve the highest steady vacuum reading. For a 340 Hopper with a moderate cam (duration 270–280°), expect idle vacuum between 10–15 inHg. If it’s below 8 inHg, your carburetor may be too large or your cam too wild.

Fuel Pressure Requirements

Most Holley and Quick Fuel carburetors need 5.5–7.0 psi. If you still have the stock mechanical pump, pressure may drop at high rpm. Consider an electric pump (e.g., Holley Blue) for sustained high-speed runs. A fuel pressure regulator set to 6.0 psi is a cheap insurance.

Ignition Timing Advance

The extra airflow from the Hopper intake requires more timing. Start with 12–14° initial timing, and set total timing to 34–36° all in by 2,800–3,000 rpm. Use a vacuum advance canister that provides full advance at cruise (about 12–15° additional). This will improve part-throttle performance and gas mileage.

Measured Horsepower Gains – The Evidence

The original article claimed 35 HP, and that number comes from multiple dyno tests. For example, Popular Hot Rodding tested a 340 with the Mopar Performance Hopper intake and a Holley 750 DP on a 1971 Dodge Demon (A-body, but same engine). Result: 278 rear-wheel HP stock vs. 314 rear-wheel HP after the swap – a 36 HP gain. On a heavier B-body, the drivetrain loss is similar, so you can expect roughly the same improvement at the wheels.

If you also add headers (like TTI or Hooker Super Comp) and a free-flowing exhaust, that 35 HP can jump to 50–60 HP. The intake and carburetor alone, however, are a solid foundation for any performance 340 build.

Complementary Modifications to Maximize the 340 Hopper

While the intake and carb swap is a huge step, consider these supporting mods to get the most out of your B-body:

  • Free-flowing cylinder heads – Even stock 340 heads respond well to a port cleanup; next step is a set of Edelbrock Performer RPM heads.
  • Camshaft upgrade – A hydraulic flat-tappet cam with 224–230° duration at 0.050” will match the Hopper’s flow range perfectly. The Mopar Performance 340 cam (P4452783) is an excellent choice.
  • Ignition system – Replace points with an electronic conversion (Mopar Electronic Ignition or MSD 6AL). The hotter spark helps burn the larger volume of fuel added by the 750 CFM carb.
  • Headers and dual exhaust – A 2.5” mandrel-bent exhaust system with free-flowing mufflers (like Flowmaster 40 series) will drop back-pressure and add another 10–15 HP.

For more ideas, browse the tech library at Classic Industries, which supplies many restoration and performance parts for B-bodies.

Frequently Asked Questions

Will the 340 Hopper intake clear a B-body hood?

In most B-body models (Charger, Coronet, Road Runner, GTX), the factory air cleaner fits without issues. However, if you’re using a tall carburetor spacer or a scoop, check hood clearance. The Hopper is about 1/2” taller than the stock iron intake, so a drop-base air cleaner may be necessary.

Do I need to upgrade the fuel pump?

If your stock mechanical pump is in good condition, it will deliver adequate fuel for street driving with a 650–750 CFM carb. For sustained 6,000+ rpm runs or drag racing, upgrade to a high-volume mechanical or electric pump.

The Mopar Performance 340 Hopper intake is an aftermarket performance part. While it is not CARB-approved, most states with emissions testing only check for a catalytic converter (if originally equipped) and OBD-II systems. Since 340 B-bodies are pre-1975, they are exempt from smog testing in many areas. Always check local laws.

Conclusion

The Mopar Performance 340 Hopper intake and carb swap is one of the most cost-effective horsepower upgrades for any 340-powered B-body. At around $400–500 for a used intake and new carburetor, you can add an honest 35 HP to the rear wheels. The installation is straightforward for anyone comfortable with wrenches, and the wail of a 340 breathing through an open plenum is worth every minute of work.

Whether you’re restoring a numbers-matching ‘69 Road Runner or building a street-driven Charger, this combination delivers the classic Mopar muscle experience: strong low-end torque, a screaming top end, and the satisfaction of doing the work yourself.