A Hemi MDS delete kit removes or disables the Multi-Displacement System on your Dodge, Jeep, or Ram engine

The Multi-Displacement System (MDS) is a fuel-saving feature built into many Hemi V8 engines made between 2005 and present. When you're cruising at steady highway speeds, MDS shuts down four of your eight cylinders, letting the engine run on just four. When you need power — accelerating, towing, or climbing a hill — all eight cylinders fire back up. The system is designed to improve fuel economy without sacrificing performance when you need it.

A Hemi MDS delete kit physically removes or electronically disables this system. Once deleted, your engine runs on all eight cylinders all the time. Owners choose to delete MDS for several reasons: some report smoother idle and acceleration, others want to avoid potential mechanical failures in the MDS components, and some straightforward prefer the feel of a full-power engine at all times. The tradeoff is that fuel economy typically drops when MDS is no longer active.

Key Takeaways

  • MDS delete kits come in two types: mechanical kits that physically remove components, and tuning kits that reprogram the engine computer to disable the system electronically.
  • Mechanical deletes require more labor and cost more upfront, but tuning deletes are simpler to install and can sometimes be reversed if you change your mind.
  • Deleting MDS will reduce your fuel economy because your engine no longer shuts down cylinders at highway speeds.
  • Some MDS delete kits may affect your vehicle's warranty or emissions compliance, depending on your vehicle's age and your location.
  • Installation difficulty ranges from moderate DIY work to a full machine shop job, depending on which kit you choose and your mechanical skill level.

How MDS works and why owners want to remove it

When your Hemi engine is running between roughly 1,200 and 3,000 RPM and you're not accelerating hard, MDS deactivates the intake and exhaust valves on cylinders 1, 4, 6, and 7. Fuel stops flowing to those cylinders, and they stop firing. Your engine essentially becomes a four-cylinder for that moment. The system is controlled by your engine computer and happens automatically — you don't feel it happen under normal driving.

The system works well on paper: fewer cylinders burning fuel means lower consumption during steady cruising. In real-world testing, owners report fuel economy improvements of 1 to 3 miles per gallon on the highway when MDS is active. However, some owners report that MDS causes a slight hesitation or roughness when the system engages and disengages, or they experience issues with the solenoids and valve lifters that control the system over time. Others straightforward prefer the sound and feel of a full eight-cylinder engine and don't want the system interfering with engine behavior.

Mechanical delete kits versus tuning-based deletes

A mechanical delete kit physically removes or blocks the MDS components. This typically means removing the MDS solenoid pack (which controls oil flow to the valve lifters), installing solid lifters or lifter blocks, and sometimes removing or capping off related hoses and lines. Because you're removing actual parts, the engine computer no longer sees MDS components to control, so the system straightforward cannot operate. Mechanical deletes are permanent — you cannot turn MDS back on without reinstalling the original parts.

A tuning-based delete (also called a software delete or ECU tune) reprograms your engine computer to ignore MDS commands. The MDS hardware stays in place, but the computer no longer sends signals to set up it. Tuning deletes are less invasive, usually take an hour or two at a shop, and can sometimes be reversed by reflashing the computer back to stock. However, tuning deletes may not work on all model years, and some shops charge $300 to $800 for the service depending on whether they use an off-the-shelf tune or custom tune your specific vehicle.

What you need to know about fuel economy and performance

Deleting MDS will reduce your fuel economy. How much depends on how much highway driving you do. If you spend most of your time in stop-and-go city traffic, you may see little change because MDS doesn't set up much in the city anyway. If you drive long highway stretches at steady speeds, you can expect to lose 1 to 3 miles per gallon compared to running with MDS active. Some owners report that the loss is worth it for the smoother engine behavior they prefer; others regret the delete once they see their fuel bills increase.

Performance gains from a delete are usually modest. Your engine does not make more horsepower or torque — it's already making full power when you need it. What changes is the feel: acceleration may seem slightly smoother because the engine is not switching between four and eight cylinders, and some owners report a more responsive throttle. If you're looking for significant power gains, a delete alone will not deliver them. Many owners combine a delete with other modifications like a cold air intake or exhaust system, but the delete itself is more about drivability than raw performance.

Installation methods and what each requires

Mechanical deletes require the most work. You need to remove the intake manifold, access the valve lifters and MDS solenoid pack, and install replacement components. Depending on your vehicle and which kit you buy, this can take 8 to 20 hours of labor. If you have machine shop experience and proper tools, you may be able to do this yourself, but many owners take their vehicle to a shop that specializes in Hemi work. Expect to pay $1,500 to $3,000 in labor alone, plus the cost of the kit itself (typically $400 to $1,200).

Tuning deletes are much simpler. You drive to a shop, they connect a laptop to your OBD-II port (the diagnostic port under your dashboard), upload a new tune file to your engine computer, and you drive away. The whole process takes 1 to 2 hours. Cost is usually $300 to $800 depending on whether the shop uses a pre-made tune or creates a custom one for your specific vehicle. Some shops can even do this remotely if you have the right equipment, though most prefer to do it in person.

Warranty and legal considerations

Deleting MDS may void your vehicle's powertrain warranty, depending on your vehicle's age and your manufacturer's warranty terms. Dodge, Jeep, and Ram dealers can see that MDS has been deleted during service, and some will refuse to cover engine-related repairs if they determine the delete caused the problem. If your vehicle is still under warranty, contact your dealer before deleting to understand what you might lose.

Emissions compliance is another consideration. In most states, deleting emissions-related systems (and MDS is tied to emissions control) on a vehicle newer than about 10 years old may violate state law. Some states allow it for off-road use only. If you live in a state with strict emissions testing, a delete could cause your vehicle to fail inspection. Check your state's emissions regulations before proceeding, or ask the shop doing the work whether they've had issues with local inspectors.

Common problems and what to watch for

The most common issue after a mechanical delete is a check engine light caused by the computer no longer detecting MDS components. A good shop will disable the related diagnostic codes when they do the delete, but some do not. If you get a light after the work, you may need to return to the shop or have a tuner disable the codes. This is usually a quick fix but can be frustrating if you weren't warned it might happen.

With tuning deletes, the main risk is using a poorly written tune. A bad tune can cause rough idle, hesitation, or even engine damage in extreme cases. This is why it's important to use a reputable tuner or shop with good reviews from other Hemi owners. If you're buying a pre-made tune online and installing it yourself, research the tuner's reputation carefully. Some shops also report that certain tunes conflict with other aftermarket modifications, so tell your tuner about any other changes you've made to the engine.

Frequently Asked Questions

Will deleting MDS make my engine louder?

Not significantly. MDS delete does not change your exhaust or intake, so engine noise stays about the same. Some owners report that the engine sounds slightly different because it's running on eight cylinders all the time instead of switching between four and eight, but the difference is subtle. If you want a noticeably louder engine, you'll need an exhaust system upgrade in addition to the delete.

Can I delete MDS myself if I have basic mechanical skills?

A tuning delete is possible for a DIYer if you're comfortable working with a laptop and following instructions, though most people take it to a shop. A mechanical delete requires removing the intake manifold and working with valve lifters, which is more involved. Unless you have significant engine work experience, a shop is the safer choice for a mechanical delete.

What happens if I sell my truck after deleting MDS?

You should disclose the delete to the buyer. Some buyers prefer a deleted engine and will pay more; others see it as a negative because of warranty concerns or fuel economy loss. If you installed a tuning delete, you can sometimes have it reflashed back to stock before selling, which may make the truck easier to sell. A mechanical delete is permanent and cannot be undone.

Does MDS delete affect towing capacity?

No. Your engine's towing capacity is determined by its horsepower and torque, which don't change with a delete. MDS delete does not add power. However, some owners report that the engine feels more responsive when towing because it's not switching between four and eight cylinders, which can feel smoother under load.

How much does a full MDS delete cost?

A tuning delete typically costs $300 to $800 at a shop. A mechanical delete costs $1,500 to $3,000 in labor plus $400 to $1,200 for the kit, depending on your vehicle and which shop you use. Get quotes from multiple shops that specialize in Hemi engines, as prices vary widely by region and shop experience.