Choosing the right supporting modifications for your HEMI MDS delete conversion is critical to unlocking both performance and long-term reliability. While disabling the Multi-Displacement System removes cylinder deactivation and eliminates the risk of collapsed lifters, it also exposes the engine to higher stresses and demands. This guide dives deep into the three essential areas: forced induction options (boosters), fuel system upgrades, and ECU (engine control unit) tuning strategies. We'll cover specific components, compatibility considerations, and real-world trade-offs to help you build a setup that matches your power goals and driving habits.

Understanding the HEMI MDS Delete Conversion

The Multi-Displacement System (MDS) was introduced on Chrysler HEMI engines to improve fuel economy by deactivating four of the eight cylinders under light load. However, MDS components—lifters, solenoids, and oil passages—are a common failure point, especially in high-horsepower builds. An MDS delete replaces the factory lifters with non-MDS versions, installs new camshafts, and often requires a different oil pump and timing set. Once MDS is removed, the engine operates at full displacement at all times, which shifts the engine's torque curve and increases cylinder pressure in every combustion event.

Because the engine is no longer designed to run on four cylinders, supporting mods must address the increased thermal load, fuel demand, and ignition requirements. Simply deleting MDS without upgrading the induction, fueling, or control systems can lead to lean conditions, detonation, or outright failure. The following sections break down each category so you can plan a coherent build.

Boosters: Superchargers and Turbochargers

Adding forced induction after an MDS delete is one of the most effective ways to increase horsepower. The non-MDS camshaft profiles typically have more aggressive lift and duration, which pair well with positive-displacement superchargers or large-frame turbochargers. The choice between the two depends on your driving style, budget, and how you intend to use the vehicle.

Superchargers

Superchargers provide instant, linear power delivery because they are belt-driven off the crankshaft. They are ideal for street-driven trucks and muscle cars where low-end torque and rapid throttle response matter more than peak power numbers.

  • Centrifugal superchargers (e.g., ProCharger, Vortech) spin at high speeds and produce boost proportional to engine RPM. They are efficient, generate less heat than blowers, and often require an intercooler. Good for builds aiming for 600–900 hp.
  • Roots-type and twin-screw superchargers (e.g., Magnuson, Whipple) use large rotors to push air directly into the intake manifold. They deliver instant boost off idle and are known for their fat torque curves. These units are heavier and produce more heat, making them better for lower RPM power.

Key considerations: Superchargers increase load on the front of the engine’s crankshaft. A strong damper and upgraded serpentine belt are recommended. Also, intercooling is critical—air-to-water intercooler setups are popular on HEMIs with magnum-style blowers.

Turbochargers

Turbochargers use exhaust gas to spool a turbine wheel, which drives a compressor on the intake side. They offer the highest power potential—many HEMI turbo builds exceed 1,000 hp—but they introduce turbo lag, especially with single-turbo configurations on large-displacement engines.

  • Single turbo (e.g., 76mm–88mm) simplifies plumbing but may produce narrow power bands. Requires careful wastegate setup to avoid boost creep.
  • Twin turbos (e.g., Garrett G30-770 or G35-1050) allow each bank to feed its own turbine, reducing lag and improving exhaust flow. More complex and expensive but offer excellent drivability.
  • Twin-scroll turbochargers split the exhaust pulses to reduce reversion and improve spool. Ideal for HEMIs with properly built headers.

Key considerations: Turbos generate massive heat, so exhaust gas temperature (EGT) monitoring and high-quality oil cooling are mandatory. The MDS delete eliminates the restrictive oil passages, but you still need a dedicated oil feed and drain setup for the turbo bearings. Consider a surge valve (blow-off valve) and a boost controller to fine-tune the curve.

For both superchargers and turbos, the MDS delete allows you to run more timing and boost because the fixed lifters eliminate the risk of collapsed MDS units causing piston-to-valve clearance issues. A reputable forced induction kit from a company like ProCharger or Magnuson can be a reliable starting point for a streetable build.

Fuel System Upgrades

Forced induction drastically increases fuel demand. A stock HEMI fuel system—pump, injectors, lines, and rail—will quickly become the bottleneck. Fuel system upgrades must be selected to deliver the correct volume at the required pressure while maintaining consistent flow across all RPM ranges.

Fuel Pumps

The factory in-tank pump on most HEMI trucks (e.g., 5.7L or 6.4L) is adequate for naturally aspirated builds up to about 450–500 hp. For boosted applications, you need a pump rated for your target horsepower. Two common approaches:

  • Drop-in high-flow pumps: Units like the Walbro 525 or 540 fit inside the stock fuel hanger. They support up to 800–1,000 hp on gasoline (less on E85 due to lower energy density). Easy installation, but may require a fuel pump voltage controller (FPVC) to manage heat and pressure at idle.
  • External pumps: Aeromotive 340 or 400 series pumps provide higher flow rates and are easier to service. They must be mounted in a surge tank or near the fuel cell to avoid cavitation. External setups require -8 or -10 AN feed lines and a return system.

Dual-pump systems are common for builds over 1,000 hp. Some shops modify the stock hanger to hold two Walbro 525s, while others use a complete replacement unit from Fore Innovations or VaporWorx. Always wire the pumps using a dedicated relay and fuse, and consider a fuel tank pressure sensor to avoid vacuum issues.

Fuel Injectors

Injectors must deliver enough fuel volume with proper spray patterns to match the increased air charge. Selecting too large an injector can cause poor idle and low-speed drivability; too small leads to high duty cycle and possible leanouts.

  • Size: For a 6.4L HEMI with a 2.9L supercharger at 10 psi, you might need 1,000–1,300 cc/min injectors. On E85, plan for 1,500–2,000 cc/min because ethanol requires roughly 30% more fuel volume per unit of air.
  • Type: Boss-style (EV14) injectors are common modern formats. Look for units with high-z (high impedance) and data sheets showing flow curves at various pressures. Brands like Injector Dynamics, FIC, or Bosch offer proven reliability.
  • Compatibility: Some late-model HEMI ECUs require high z-flow injectors with specific latency settings. Standalone ECUs can compensate for almost any injector, but reflashed stock ECUs may have limited tables.

After the MDS delete, the cylinder deactivation camshaft lobes are replaced with full-profile lobes, increasing overlap and changing cylinder filling. That may alter pulse width needs; always consult a tuner or injector calculator.

Fuel Lines and Rails

Once your pump and injectors are set, the lines must carry the fuel without restriction. Stock plastic lines on modern HEMIs are adequate up to about 600 hp, but beyond that they can burst or flow insufficiently under extended wide-open throttle.

  • Material: Stainless steel braided hose (e.g., -6 AN for 600–800 hp, -8 AN for 800–1,200 hp) is preferred for durability and heat resistance. PTFE-lined hose resists ethanol corrosion.
  • Rails: Stock fuel rails may distribute fuel unevenly under high flow. Aftermarket cross-over rails (full return style) equalize pressure across all cylinders. Many HEMI builds use a billet rail with internal fuel passages designed for high boost.
  • Regulator: A boost-referenced fuel pressure regulator (e.g., Aeromotive 13139) will raise fuel pressure by the amount of boost pressure, maintaining a constant differential across the injectors. This is critical for boosted HEMIs to avoid leaning out when boost comes on.

Always use a dedicated fuel return line back to the tank—the stock return-less system on many HEMI vehicles cannot handle the flow of an aftermarket pump. A fuel system from Fore Innovations comes as a complete kit with hanger, pumps, lines, and regulator.

ECU Options for Optimal Performance

An MDS delete combined with a different camshaft and forced induction will not run correctly on the factory ECU calibration. The stock ECU cannot properly control timing, fueling, and variable valve timing (VVT) without reprogramming. Three paths exist: reflashing the stock ECU, using a piggyback controller, or switching to a standalone aftermarket system.

Reflashing the Stock ECU

Tuning the factory Mopar ECU through software like HP Tuners or DiabloSport is the most common and cost-effective route for mild boost and cam setups. A competent tuner can disable MDS codes, adjust the camshaft position sensor to match the new grind, and create a custom fuel/spark map.

  • Advantages: Retains all OEM features (cruise control, driveability aids, DBW throttle calibration, transmission control). Lower cost (typically $400–$800 for a custom tune plus tuning license).
  • Disadvantages: Limited output capacity—stock ECUs often struggle with engines above ~900 hp due to injector latency limits and scaling restrictions. Also, tune revisions require the tuner to have remote or in-person access.

For builds using a supercharger kit with a supplied tune (like Magnuson or Whipple), a reflash is usually sufficient as long as you stay within the kit's fuel system support. However, aggressive or custom cam grinds may require more extensive recalibration, including changes to the VVT tables if you retained variable cam timing.

Piggyback ECUs and Boost Controllers

Some enthusiasts add a piggyback device like a MSD Atomic EFI or Haltech ECU that intercepts sensor signals and modifies outputs to trick the stock ECU. This approach is less common for modern HEMIs because the stock ECU is heavily integrated with the transmission and CAN bus. Piggybacks can add extra fuel injector drivers or boost control, but they add complexity and potential failure points. Better for enthusiast projects than daily-driven builds.

Standalone ECU Systems

A standalone engine management system gives you total control: fuel, spark, boost control, VVT (if retained), traction control, and data logging. This is the recommended route for builds exceeding 900 hp, including those with nitrous, compound turbos, or race-gas/E85 switchability.

  • Popular options: Holley Dominator EFI, MoTeC M1, Haltech Elite 2500, or a DIY system based on a MegaSquirt. The Holley Dominator is especially popular for HEMI swaps and high-builds because it supports up to 16 injectors, 8 coils, and flexible I/O.
  • Wiring complexity: Standalone ECUs require a complete rewire of the engine harness. Many aftermarket companies sell plug-and-play adapters for older HEMI swaps (e.g., PSI Conversion), but MDS-delete 2010+ vehicles may need a custom harness. Expect 20–40 hours of wiring or a $1,500–$2,500 harness from a specialist.
  • Tuning capability: Tuners can set up boost-by-gear, nitrous timers, anti-lag, and sensor failsafes. Data logging via CAN bus allows real-time analysis of fuel pressure, lambda, and knock. Standalone ECUs also accommodate E85 flex fuel sensors more easily than stock ECUs.

Downsides: cost ($1,500–$3,500 for ECU plus harness), loss of some factory features like OE cruise control (though many standalone systems can emulate it), and a steeper learning curve for the tuner. For a dedicated performance vehicle, the trade-off is often worth it.

Additional Supporting Modifications

While boosters, fuel system, and ECU are the three core pillars, several other areas deserve attention after an MDS delete.

Cooling System

MDS deletion combined with forced induction significantly raises coolant and oil temperatures. Upgrading to a larger aluminum radiator, high-flow water pump, and a thermostat rated for higher flow (e.g., 180°F versus 195°F) helps. If using a turbo, an oil cooler is mandatory—consider a thermostatic sandwich plate adapter with a 25-row cooler. For superchargers, an air-to-water intercooler system with an auxiliary electric pump and dedicated heat exchanger can keep charge air temperatures in check.

Transmission and Drivetrain

A boosted HEMI after MDS delete can easily exceed the torque capacity of the factory 8HP70 or 6R80 transmissions. A torque converter upgrade, stronger clutches/bands, and a tune that limits low-RPM torque spikes can preserve the transmission. The rear axle also needs attention—many HEMI truck owners upgrade to a 10.5" or 11.5" axle from a 3500-series truck, or use aftermarket axles from Yukon or Strange.

Putting It All Together: Sample Build Approaches

To illustrate how these mods interact, consider two common scenarios:

  • Street-legal 650 hp daily driver: Start with a non-MDS cam (e.g., 218°/224° at .050"), a centrifugal supercharger like a ProCharger P-1SC with 8 psi on pump gas, Walbro 525 pump, 1,000 cc injectors, reflashed stock ECU via HP Tuners. Add a heat exchanger for the intercooler and a 180° thermostat. Total budget: $5,000–$7,000 in parts, plus tuning.
  • 1,000+ hp track/weekend weapon: Twin turbos (Garrett G35-1050s), custom stainless headers, dual Walbro 450s in a Fore Innovations hanger, 1,650 cc injectors (on E85), Holley Dominator EFI, full harness, and a built transmission with a PCS controller. Expect $15,000–$20,000 in engine and fuel components alone.

Whichever path you choose, remember that every component must be matched to your specific MDS delete cam profile and forced induction setup. Work with a reputable shop that specializes in HEMI builds, and always verify your tune on a dyno with wideband O2 readings. An MDS delete opens the door to real power, but only if the supporting mods are engineered to work together.

Additional reading: For an overview of MDS delete kits and installation, consult a detailed guide on HEMI lifter replacement. For forced induction parts, visit the manufacturer sites listed in this article. And never skip the final step—a professional dyno tune to ensure air-fuel ratios, timing, and fuel pressure are within safe margins.