A 5.7 Hemi MDS delete kit removes or disables the Multi-Displacement System that your engine uses to save fuel
The 5.7-liter Hemi engine in Dodge, Jeep, and Ram vehicles comes with Multi-Displacement System (MDS) technology built in. MDS shuts down half of your engine's cylinders when you're cruising at steady speeds — typically on the highway — so the engine burns less fuel. A delete kit physically removes or electronically disables this system, forcing all eight cylinders to run all the time.
Owners install delete kits for different reasons: some want more consistent engine performance, others dislike the slight vibration or noise MDS creates when it switches between four and eight cylinders, and some straightforward prefer the sound and feel of a full-power engine. The trade-off is that you'll use more fuel once MDS is gone, because your engine is always running at full displacement.
Key Takeaways
- MDS automatically disables four cylinders during light-load driving to reduce fuel consumption, and a delete kit removes or disables this feature permanently.
- Delete kits come in two types: mechanical kits that physically remove components, and tuning kits that reprogram the engine computer to turn MDS off.
- Removing MDS will increase your fuel consumption noticeably, typically by 1 to 3 miles per gallon depending on your driving habits.
- Some delete kits require engine computer reprogramming, which may affect your vehicle's emissions system and warranty coverage.
- Installation difficulty ranges from straightforward (tuning only) to moderately complex (mechanical removal), depending on which kit you choose.
How MDS works and why it matters to your fuel economy
When your 5.7 Hemi is running at steady highway speeds with light throttle input, MDS deactivates the intake and exhaust valves on cylinders 1, 4, 6, and 7. The pistons in those cylinders still move, but they're not drawing in fuel or air, so they're not doing any work. Your engine effectively becomes a 5.7-liter four-cylinder, burning much less fuel to maintain your speed.
The system switches between four and eight cylinders seamlessly — you may not even notice it happening. However, some owners report a slight hesitation, vibration, or change in engine sound when the transition occurs. For drivers who spend a lot of time on the highway, MDS can improve fuel economy by 1 to 3 miles per gallon. For city driving or towing, MDS activates less often because the engine is under higher load more of the time.
Mechanical delete kits versus tuning-only kits
Mechanical delete kits physically remove or modify the components that MDS uses to control valve operation. These kits typically replace the variable valve timing solenoids and delete the oil lines that feed them. A mechanical delete is permanent — once installed, MDS cannot be reactivated without reinstalling the original parts. Installation usually takes 4 to 8 hours and requires removing the valve covers and some engine accessories.
Tuning kits reprogram your engine's computer (called the Powertrain Control Module, or PCM) to disable MDS electronically. No physical parts are removed. Tuning is faster to install — often just a few hours at a shop — and it's reversible if you want to turn MDS back on later. However, tuning may trigger a check engine light or affect emissions system monitoring, depending on the tuner and your vehicle year.
Mechanical kits tend to cost between $400 and $800 in parts, plus labor. Tuning kits typically run $300 to $600. Some owners combine both approaches for maximum reliability, though this is less common.
What happens to your fuel economy after deletion
Removing MDS means your engine runs all eight cylinders all the time, even when you're cruising at steady speeds. This increases fuel consumption noticeably. Most owners report losing 1 to 3 miles per gallon in highway driving, where MDS would normally be active. City driving may see smaller losses because MDS is less active in stop-and-go traffic anyway.
The exact impact depends on your driving style, vehicle weight, and whether you're towing. A Ram 1500 driven mostly on the highway will see a bigger fuel economy drop than a Jeep Wrangler driven mostly in town. If fuel economy is important to you, a delete kit is a trade-off worth calculating before installation.
Warranty and emissions system concerns
Disabling or removing MDS may void your vehicle's powertrain warranty, depending on your manufacturer and the specific kit you use. Dodge, Jeep, and Ram dealers can see that MDS has been disabled, either through a tuning file or by the absence of mechanical components. Some dealers will refuse warranty work on engine-related issues if they discover a delete kit has been installed.
MDS is also part of your vehicle's emissions control system. Tuning kits that disable MDS without addressing emissions monitoring can trigger a check engine light. Some tuners account for this by adjusting other engine parameters, but results vary. If you live in a state with emissions testing, a delete kit may cause your vehicle to fail inspection, depending on how the kit handles emissions codes.
Installation: what to expect and what can go wrong
Mechanical delete installation requires removing the valve covers, fuel rails, and intake manifold to access the variable valve timing solenoids and their oil supply lines. This is intermediate-level work — not beginner-friendly, but manageable for someone with basic engine knowledge and the right tools. Most shops charge $500 to $1,200 in labor on top of parts cost.
Tuning installation is simpler: you either connect your vehicle to a laptop at a tuning shop, or you use a handheld tuner device to reprogram the PCM yourself. This takes 1 to 3 hours. The main risk is choosing a tuner that doesn't account for emissions monitoring or other engine systems, which can cause drivability issues or warning lights.
Common problems after deletion include rough idle, hesitation during acceleration, or a persistent check engine light. These usually mean the tuning file needs adjustment or a mechanical component wasn't installed correctly. Choosing a reputable tuner or shop is important — budget delete kits from unknown manufacturers sometimes cause more problems than they solve.
Alternatives if you want to reduce MDS without a full delete
If you want to reduce MDS activity without removing it entirely, some tuners offer MDS disable on demand — a feature that lets you turn MDS off through a switch or button while keeping the system available. This gives you the option to run all eight cylinders when you want performance, but still benefit from MDS fuel savings during normal driving.
Another option is a performance tune that adjusts MDS thresholds rather than disabling it completely. These tunes can make MDS set up less often or at different engine speeds, giving you a middle ground between full deletion and stock operation. Performance tunes also typically add horsepower and torque across the board.
Frequently Asked Questions
Will a delete kit make my Hemi louder?
Yes, typically. Running all eight cylinders all the time produces a deeper, more aggressive exhaust note, especially under acceleration. Some owners like this; others find it too loud for daily driving. The difference is most noticeable on the highway where MDS would normally be active.
Can I reinstall MDS after deleting it?
With a tuning kit, yes — the tuner can reprogram your PCM back to stock settings. With a mechanical delete, you would need to reinstall the original solenoids and oil lines, which is possible but expensive. Most owners who delete MDS do not plan to reinstall it.
Does deleting MDS add horsepower?
Not directly. Removing MDS does not change how much power your engine makes. However, some owners pair a delete kit with a performance tune that does add horsepower. A delete kit alone will not improve acceleration or top speed.
Will my vehicle fail emissions testing with a delete kit?
It depends on your state's testing procedure and how the delete kit handles emissions codes. Some kits trigger a check engine light, which causes an automatic failure. Others disable MDS without affecting emissions monitoring. Check your local testing requirements before installation.
How much does a full delete cost installed?
Mechanical delete kits typically cost $900 to $2,000 total (parts plus labor), while tuning-only kits run $300 to $1,200 depending on the tuner and whether you install it yourself. Prices vary by region and shop.