Understanding the HEMI Engine and the MDS System

The HEMI engine family, particularly the 5.7L, 6.1L, and 6.4L variants found in Ram trucks, Dodge Chargers, Challengers, and Jeep Grand Cherokees, is celebrated for its hemispherical combustion chambers. This design promotes superior flame propagation and volumetric efficiency, resulting in strong low-end torque and high-rpm power. However, to meet fuel economy regulations, Fiat Chrysler Automobiles (now Stellantis) introduced Multi-Displacement System (MDS) on many HEMI engines. MDS deactivates four of the eight cylinders under light load conditions, allowing the engine to run as a V4. While effective for fuel savings — typically a 5–10% improvement in highway driving — the system introduces compromises for performance-oriented owners.

The MDS hardware includes solenoids that disable lifters on cylinders 1, 4, 6, and 7. These solenoids, activated by engine oil pressure, collapse the lifters to stop valve movement. Over time, MDS lifters have been known to fail, causing ticking noises or camshaft damage. Additionally, the instantaneous transition between V8 and V4 modes can create a slight hesitation in throttle response. For enthusiasts building a high-performance HEMI, removing the MDS system is often the first step toward reliability and maximum power.

Why Delete MDS? The Performance Case

An MDS delete removes the cylinder deactivation hardware and replaces it with standard non-MDS lifters, a different camshaft (if desired), and a tuner to disable the software. The benefits are tangible:

  • Increased horsepower and torque: Without MDS, the engine operates continuously as a V8, allowing for optimized air/fuel mixtures and ignition timing. Many builds see gains of 20–40 hp at the wheels even before adding other parts.
  • Improved throttle response: The lag caused by cylinder reactivation is eliminated. The engine responds instantly to throttle inputs, crucial for track or spirited driving.
  • Enhanced engine sound: The exhaust note becomes full and aggressive, especially with aftermarket exhausts. No more sudden sound changes during highway cruising.
  • More reliable high-stress performance: MDS components are a known weak point when pushing high horsepower or towing heavy loads. Deleting them reduces the risk of lifter failure and camshaft wear.

However, MDS delete is not an all-or-nothing decision. Some owners retain MDS for daily commuting and only disable it via tuning. For a dedicated high-performance build, though, mechanical removal ensures no future failures.

Core Components of the Build

This cost analysis focuses on three main upgrades: the MDS delete itself, a heavy-duty clutch (McLeod), and an intake system (AEM). We’ll also touch on supporting modifications often included in a comprehensive build.

1. MDS Delete Kit

A complete MDS delete kit includes replacement lifters, pushrods, and often a new camshaft. Prices vary based on brand and whether you reuse the stock cam or upgrade. Typical costs range from $300 to $600 for a base kit (lifters + gaskets) up to $800–$1,200 if a performance camshaft is included. Major brands include Texas Speed, Comp Cams, and BTR. A quality kit ensures proper oiling and compatibility with your HEMI generation (Gen III vs. Gen IV).

Some enthusiasts also purchase a custom tune to disable MDS in the ECU. This can be done via handheld tuners (DiabloSport, HP Tuners) costing $400–$700. However, tuning alone does not remove the mechanical risk of lifter failure — only a physical delete does that.

2. McLeod Clutch

McLeod Racing is a leading manufacturer of high-performance clutches for both manual and automatic applications. For HEMI builds, the McLeod RXT and RST twin-disc clutches are popular. They offer holding capacity up to 1,200 hp while maintaining a near-stock pedal feel. A McLeod clutch kit typically includes a flywheel, pressure plate, disc(s), throwout bearing, and pilot bearing. Prices range from $500 for a single-disc street unit to $1,200 for a twin-disc race-oriented setup. Installation labor adds $400–$800 if not done at home.

Choosing the right clutch depends on power goals and driving style. For drag racing, a heavier twin-disc provides better bite. For street driving with occasional track use, a single-disc street twin offers smooth engagement. McLeod also offers hydraulic throwout bearings to improve clutch release consistency.

3. AEM Intake

AEM Induction builds cold air intake systems that replace the restrictive factory airbox. Their HEMI intakes feature a large conical filter, mandrel-bent aluminum or composite tubing, and heat shields to isolate hot engine air. Gains are typically 10–15 hp and 10–15 lb-ft of torque on a naturally aspirated HEMI. Prices range from $300 to $500 for a typical Ram 1500 or Charger kit. Some applications include an oiled or dry filter (requires cleaning vs. no maintenance). AEM also provides optional pre-filters for dusty environments.

While an intake alone yields modest gains, it is a critical foundation for additional modifications like headers or a camshaft. The increased airflow must be matched by the engine’s ability to ingest and expel air, making the intake an excellent early upgrade.

Supporting Modifications and Their Costs

A high-performance build rarely stops at the three components above. To fully benefit from MDS delete, a new camshaft is standard. Performance camshafts increase valve lift and duration, shifting power to the mid- and upper-RPM ranges. A cam kit (cam, lifters, springs, retainers, pushrods, and timing set) can cost $800–$1,500. Additionally, replacing the oil pump and timing chain is recommended for reliability when the front cover is off.

Headers improve exhaust flow. Long-tube headers from brands like Kooks or American Racing Headers cost $900–$1,500. Pairing them with a high-flow catalytic converter or cat-back exhaust system ($500–$1,000) completes the breathing cycle.

A professional tune is essential after any camshaft or intake change. A dyno tune from a reputable shop runs $400–$800. Without a tune, the engine may run lean, misfire, or lack response.

Detailed Cost Breakdown

Below is a realistic cost range for a complete high-performance HEMI MDS delete build including the named components and supporting mods. All prices are in USD as of early 2025.

  • MDS Delete Kit (lifters, pushrods, gaskets): $350 – $600
  • Performance Camshaft Kit (with springs, retainers): $800 – $1,500
  • Timing Chain & Oil Pump (upgraded): $200 – $400
  • McLeod Clutch Kit (single or twin disc): $500 – $1,200
  • AEM Cold Air Intake: $300 – $500
  • Long-Tube Headers (optional but recommended): $900 – $1,500
  • Exhaust System (cat-back): $500 – $1,000
  • Professional Tune (dyno): $400 – $800
  • Labor (if not DIY — engine bay work, clutch installation): $1,500 – $3,000 (depending on shop rate and scope)
  • Miscellaneous (fluids, gaskets, fasteners, coolant): $150 – $300

Estimated Total (parts only, DIY installation): $3,200 – $5,800
Estimated Total (with professional labor and all supporting mods): $5,500 – $9,500

These ranges reflect varying quality levels and whether you opt for cam/headers immediately or stage the build. A minimal MDS delete with clutch and intake, without cam or headers, will be at the lower end. The high-performance build with all supporting mods falls at the upper end.

Performance Gains Expected

With the described build — including a moderate performance camshaft, headers, MDS delete, McLeod clutch, and AEM intake — a 5.7L HEMI can see gains of 80–120 horsepower at the crankshaft. At the wheels, that translates to roughly 380–420 hp (up from stock 335–360 hp depending on model). A 6.4L HEMI can gain 90–130 hp, reaching 500+ wheel horsepower naturally aspirated. Torque improvements are equally impressive, often exceeding 450 lb-ft at the wheels on a 6.4L.

The McLeod clutch ensures that this power is transmitted reliably without slipping. The AEM intake supports the increased air demand, while the tune optimizes fuel delivery and timing. Real-world driving becomes more responsive, with the engine pulling hard to redline. Throttle response improvements are especially noticeable when accelerating from highway speeds or passing.

Installation Considerations: DIY vs. Professional

Installing an MDS delete kit and camshaft requires intermediate to advanced mechanical skills. You must remove the intake manifold, cylinder heads (or at least the lifters via the head bolt method), front timing cover, oil pan, and transmission (for clutch replacement). Special tools like a harmonic balancer puller, camshaft retainer tool, and torque wrenches are essential. A full clutch replacement on a HEMI typically takes 6–10 hours for an experienced mechanic; do-it-yourself can take a full weekend or more.

If you are not comfortable with engine internals, professional installation is strongly recommended. A reputable shop with HEMI experience can complete the job in two to three days. Expect labor costs of $100–$200 per hour. While expensive, a professional install reduces the risk of oil leaks, timing misalignment, or lifter failure due to improper assembly.

Reliability and Maintenance After the Build

Once MDS is removed, the engine becomes a traditional non-MDS HEMI. Long-term reliability can actually improve because the common lifter failure point is eliminated. However, the performance camshaft will have a more aggressive lobe profile, which increases valve train stress. High-quality lifters (such as Johnson or Melling) and proper break-in procedures are critical. Oil changes should be performed every 3,000–5,000 miles with full synthetic oil (5W-20 or 5W-30 per brand recommendations).

The McLeod clutch has a specific break-in period (typically 500–800 miles of gentle driving) during which hard launches or high-rpm slipping should be avoided. After break-in, the clutch holds strong for street and strip use.

The AEM intake filter requires periodic cleaning (every 25,000–50,000 miles depending on conditions). Re-oiling must be done sparingly to avoid contaminating the MAF sensor. AEM provides detailed instructions for each kit.

Comparing Costs: MDS Delete vs. Forced Induction

Some owners consider a supercharger or turbo kit instead of a cam/head build. For comparison, a centrifugal supercharger kit can cost $5,000–$8,000 installed on a stock HEMI, delivering 100–200 hp gains. However, forced induction adds heat and complexity, and often requires upgrading the fuel system and cooling. An MDS delete build with cam and headers is more affordable, preserves drivability, and still adds substantial power. The choice depends on ultimate power goals and budget. For 500–600 wheel horsepower naturally aspirated, the MDS delete route is cost-effective.

External Resources and Further Reading

For more detailed information on specific components, refer to the manufacturers:

  • Brian Tooley Racing — camshafts and MDS delete kits for HEMI engines
  • McLeod Racing — clutch systems for HEMI applications
  • AEM Intakes — cold air intake systems for Ram, Dodge, and Jeep
  • HP Tuners — tuning software for disabling MDS and optimizing performance

Additionally, forums like RamForum and ChargerForumz offer real-world build threads and cost experiences from fellow owners.

Conclusion: Is It Worth the Investment?

A high-performance HEMI MDS delete build featuring a McLeod clutch and AEM intake is a proven path to significantly more power, reliability, and driving enjoyment. The total investment — ranging from roughly $3,200 for a DIY parts-only build to $9,500 for a fully professional installation with all supporting mods — is reasonable relative to the gains. Enthusiasts who value throttle response, a vibrant exhaust note, and peace of mind from eliminating a known failure point will find this upgrade highly rewarding.

For those on a tighter budget, starting with just the MDS delete kit and a clutch, while reusing the stock cam and tuning the MDS off, can still improve reliability and reduce future repair costs. However, the best results come from a comprehensive approach that addresses airflow, fueling, and drivetrain. Whether you choose to install yourself or hire a shop, plan the build carefully, choose quality parts, and enjoy the transformation of your HEMI into a true performance machine.