The Chrysler B‑body—think Road Runner, Charger, Super Bee, and Coronet R/T—represents the golden era of Mopar muscle. With a factory 440‑ or 383‑based build, many of these cars came from the assembly line with roughly 400 horsepower (gross) on tap, but that was just the starting point. Today’s enthusiasts know that a well‑planned set of upgrades can push that 400 hp foundation comfortably past the 500‑horsepower mark, transforming a weekend cruiser into a street‑legal predator. This guide covers the ten most effective classic Mopar performance upgrades for your B‑body, each chosen for real‑world gains, reliability, and respect for the car’s original character. Whether you’re building a torque‑monster street machine or a track‑day contender, these modifications deliver measurable results without requiring a complete chassis teardown.

1. Upgraded Carburetor

A stock Carter AFB or Holley 750 CFM carburetor served the 400‑horse era well, but modern aftermarket carbs offer far better fuel atomization, vacuum secondary calibration, and ease of tuning. Replacing the original unit with a 850‑or 950‑CFM four‑barrel can increase airflow by nearly 25%, directly improving volumetric efficiency. Look for carburetors designed with annular boosters and billet metering blocks, which provide crisper throttle response and consistent air‑fuel ratios across the rev range.

For B‑body street use, a double pumper style (mechanical secondaries) can deliver instant punch, while a vacuum secondary model offers better driveability for daily driving. Brands like Holley, Quick Fuel, and Edelbrock offer direct‑fit options for the Mopar spread‑bore bolt pattern. Don’t overlook the importance of a proper linkage kit and return spring—these small details prevent hesitation and dangerous sticking.

Key considerations:

  • Match CFM to engine displacement and intended rpm range (850–950 CFM for 440‑based builds)
  • Annular boosters improve low‑speed velocity and driveability
  • Mechanical secondaries are favored for drag racing; vacuum for street

2. High‑Performance Intake Manifold

The stock cast‑iron intake manifold on most B‑body 440s and 383s is heavy and restrictive, especially in the plenum area. Swapping to an aluminum performance intake instantly sheds about 25–35 pounds and opens up the flow path. A dual‑plane design like the Edelbrock Performer RPM provides excellent low‑ and mid‑range torque, while a single‑plane model (e.g., Holley Strip Dominator) shifts power upward for all‑out top‑end runs.

For a 400‑to‑500 hp transition, a dual‑plane intake is the smarter choice—it preserves street manners while still supporting peak numbers well above 500 hp. Cylinder head port matching and careful gasket selection are critical; even a tiny mismatch can cost 10–15 horsepower. Consider a phenolic spacer to reduce heat soak, which improves intake charge density on hot summer days.

Pro tip: If you already have aftermarket heads, verify the intake bolt angle and port height. Many Mopar intakes are designed for factory head dimensions and may require minor grinding to match larger runners.

3. Performance Camshaft

Upgrading the camshaft is arguably the single biggest power multiplier for a naturally aspirated Mopar big‑block. A stock 440 cam usually lifts around 0.485 in. with 268° duration; swapping to a hydraulic roller or flat‑taper cam with 0.550 in. lift and 280°–290° advertised duration can unlock an additional 60–80 horsepower. The lobe separation angle (LSA) should be chosen based on desired idle quality and rpm peak—108–110° LSA for a choppy race idle, 112–114° for street civility.

Don’t forget matched valvetrain components: performance pushrods, hardened rocker arms, and double‑valve springs are mandatory to avoid float at high rpm. For B‑body builds targeting 500+ hp, a cam with around 240° duration @ 0.050 in. is a reliable starting point. Use a cam degreeing kit to verify installation accuracy—even a 2° error can shift the power band significantly.

Cam comparison for 440 B‑body:

  • Street Performance: 0.530 in. lift, 278° duration, 114° LSA – good idle, broad torque
  • Race/Strip: 0.590 in. lift, 290° duration, 108° LSA – rough idle, peaky power
  • Compromise: 0.560 in. lift, 284° duration, 110° LSA – aggressive sound, strong mid‑range

4. Headers and Exhaust System

Stock B‑body manifolds are notoriously restrictive, especially the heat‑crossover design that plugs the exhaust flow path. Switching to long‑tube headers (1⅞ in. primary, 3 in. collector) can pick up 25–40 horsepower by reducing back pressure and allowing the cylinders to scavenge efficiently. Look for 304 stainless steel headers for corrosion resistance, or ceramic‑coated mild steel for heat management.

A full dual exhaust with 2½ in. or 3 in. mandrel‑bent tubing, an H‑pipe or X‑pipe crossover, and free‑flowing mufflers (such as Flowmaster 40s or Magnaflow) completes the system. The scavenging effect of an X‑pipe is proven to boost both torque and throttle response, especially in the mid‑range where B‑bodies live on the street. Don’t forget gasket upgrades: copper or multi‑layer steel gaskets resist blow‑out better than cheap paper variants.

Sound and power note: Headers with 1⅞ in. primaries support up to 550 hp; 2 in. primaries are overkill unless exceeding 600 hp.

5. Upgraded Ignition System

Increasing cylinder pressure and rpm demands a hotter, more consistent spark. A modern electronic ignition conversion (replacing points with a petronix or MSD distributor) provides crisp timing and eliminates mechanical wear. Pair it with a high‑output coil (e.g., MSD Blaster 2 or 8207) and low‑resistance spark plug wires to ensure full energy reaches the plugs.

Cratering the spark plug gap to 0.045 in. (from 0.035 in.) can improve combustion efficiency without misfire, but only if the coil delivers enough voltage. A programmable ignition box (like MSD 6AL) offers a built‑in rev limiter and adjustable timing curves—invaluable when tuning for 500+ hp. For carbureted B‑bodies, add a vacuum advance module tuned to provide about 10° of additional advance at cruise for better fuel economy.

Part list for a solid ignition upgrade:

  • Electronic conversion kit (PerTronix Ignitor II or MSD Pro Billet distributor)
  • High‑output ignition coil (0.7 ohm or less primary resistance)
  • 8.5mm silicone spark plug wires with weatherproof boots
  • Iridium spark plugs (heat range 5–7 depending on compression)

6. Cold Air Induction

While a cold air intake on a carbureted engine isn’t as straightforward as on a fuel‑injected car, the principle remains the same: cooler, denser air produces more oxygen per stroke. For B‑bodies, a simple open element filter housing with a 14 in. × 3 in. element can draw air from the cowl or wheel well. Many aftermarket companies offer “ram air” kits that seal against a factory‑style hood scoop or headlight duct.

At 500+ hp, even a 10°F reduction in intake air temperature can yield 3–5 horsepower. More importantly, consistent air density helps maintain tune stability. Use a cotton gauze or synthetic filter with low restriction. Avoid cheap “chrome” housings that leak at the base—spend the extra money on a sealed, radiused lid assembly.

Installation tip: Duct fresh air from the front grille or the pinch‑weld area below the battery tray for maximum pressure differential. Never recirculate hot engine bay air.

7. High‑Performance Fuel Pump

Stock mechanical fuel pumps on late‑model B‑bodies are adequate for 400 hp, but as fuel demand increases with the previous upgrades, volume and pressure become critical. At 500 hp, a typical big‑block requires about 60 gallons per hour (gph) at 6–8 psi. An aftermarket mechanical pump (like Holley’s 12‑1000) or a low‑pressure electric pump (e.g., Carter P4594) ensures consistent delivery under wide‑open throttle.

Don’t forget the fuel lines: ⅜ in. steel or braded nylon lines are the minimum for 500‑plus horsepower. If you’re running an electric pump, install a safety relay that ties into the ignition circuit and a fuel pressure regulator with a return line to prevent pressure spikes. A high‑flow filter (10‑micron for electric pumps) protects precision carburetor metering blocks.

Flow rate guide:

  • 400–500 hp: 60–80 gph mechanical pump
  • 500–600 hp: 80–100 gph electric with regulator
  • Above 600 hp: dual electric pumps or a high‑volume belt‑driven unit

8. Transmission Upgrade

Your B‑body’s TorqueFlite 727 or 904 automatic, or a A‑833 four‑speed manual, can handle 400 hp in stock trim, but adding 100‑plus more horsepower exposes weak links in clutch packs, bands, and planetary gearsets. An upgraded transmission with a shift kit, hardened clutches, and a high‑stall torque converter (around 2800–3200 rpm for big‑blocks) can transform the car’s acceleration.

For automatics, a valve body upgrade (e.g., TransGo TF‑2 or Turbo Action) reduces shift overlap and quickens shifts under load. Manual cars benefit from a McLeod racing clutch (dual disc for 500 hp) and a short‑throw shifter with bronze bushings. Gear ratio choices in the transmission may not change, but a lower final drive (rear end) often compensates—more on that next.

Key upgrade paths:

  • 727 automatic: billet servo, 5‑pinion planet, Kevlar bands
  • A‑833 manual: steel fork, cryo‑treated gears, McLeod flywheel
  • Torque converter: 9.5 in. diameter, 3000 stall, low‑balloon design

9. Rear End Gear Ratio Change

Even with 500 hp on tap, a B‑body will feel sluggish if the rear axle ratio is too high (numerically low). The factory often used 2.94:1 or 3.23:1 gears for highway cruising. Swapping to 3.55:1 or 3.73:1 dramatically improves effective acceleration. The engine spends more time in the meat of its power band, especially with a cam that peaks above 4500 rpm.

Choose a gear ratio based on tire diameter and intended use:

  • 3.55:1 – excellent all‑around street gear, works with 26–28 in. tires
  • 3.73:1 – strong low‑end, good for drag racing without sacrificing highway manners
  • 4.10:1 – dedicated strip gear, top speed limited

Install a limited‑slip differential (Sure‑Grip) to put the power down on corner exits; a welded spider‑gear “posi” is fine for straight‑line but harsh on driveline parts. Make sure the pinion yoke and U‑joints are rated for the increased torque—a slip yoke failure can destroy the tailshaft housing.

10. Suspension and Chassis Upgrades

Adding 100 horsepower is pointless if the car won’t hook up. B‑body Mopars came with torsion bar front suspension and leaf springs rear, which can be tuned for traction without a full custom setup. Start with adjustable rear leaf spring shackles and pinion snubbers to control axle wrap. A set of traction bars (e.g., CalTracs) prevent spring wind‑up and plant the tires under hard launch.

Up front, firm up the torsion bars (1.06 in. diameter for big‑blocks) and replace the rubber bushings with polyurethane for sharper steering response. A rear sway bar (factory option if not already equipped) significantly reduces body roll, making the car more predictable at higher cornering speeds. Don’t overlook shocks: adjustable gas shocks (like Koni or QA1) allow fine‑tuning of rebound and compression.

Chassis checklist for 500‑plus horsepower:

  • Subframe connectors (welded, not bolted) – eliminate body flex
  • Pinion snubber – adjust for ¼ in. clearance
  • Rear shock relocation brackets – improve launch angle
  • Steering box rebuild – manual with firm ratio, or Borgeson power steering upgrade

Conclusion

Pushing a classic Mopar B‑body from 400 to over 500 horsepower is not only achievable—it’s the natural next step for anyone who wants to unlock its true potential. The ten upgrades outlined here form a coherent, progressive approach that balances cost, effort, and results. Start with the foundation: carburetor, intake, and ignition improvements, then move to the camshaft and exhaust. Once the engine pulls hard, shore up the transmission, rear end, and chassis to handle the extra power reliably. When each component is matched correctly, the result is a B‑body that runs quicker, sounds angrier, and remains a joy to drive on both street and strip. For deeper technical data, consult resources like Summit Racing for component specifications, For B‑Bodies Only for community build logs, and Hot Rod Magazine for dyno‑tested combinations. Choose your upgrades wisely, and that 400 horsepower bench‑race figure will soon be a fond memory.