Best MDS Delete Kit for 5.7 / 6.4 Hemi — What a Complete Delete Actually Includes

TL;DR: An MDS delete is not one part, it is four things that have to happen together — non-MDS lifters, a non-MDS valley tray (or the correct oil-galley plugs), a camshaft the lifters are valid on, and a PCM tune with the feature disabled. Skip any one and the engine either throws codes, bleeds oil pressure out of the now-open MDS galleys, or wipes the new lobes. Which kit you buy should follow from how far into the engine you are already going: if the lifters are coming out anyway because one collapsed, adding the camshaft costs almost nothing in extra labor and removes the failure mode permanently. Buying a "delete kit" that turns out to be sixteen lifters in a box is the most common mistake on this job.

If you searched "MDS delete kit," one of two things is true. Either your Hemi is ticking, misfiring on a cylinder that MDS deactivates, and a shop has told you a lifter collapsed — or you are planning a cam swap and just found out the grind you want is not compatible with the deactivating lifters. Both roads end in the same place. Here is how to confirm your engine even has MDS, what a complete delete has to contain, how the suppliers differ, and the order the work goes in.

Gate 1 — Does your Hemi actually have MDS?

Multi-Displacement System shuts down cylinders 1, 4, 6 and 7 under light load using special two-piece hydraulic lifters that collapse on command. Oil pressure routed through solenoids in the valley tray unlocks a latching pin inside the lifter, the lifter goes slack, and those four valves stop opening. It works. It also means eight of your sixteen lifters are mechanically more complex than a normal hydraulic roller — and complexity in a lifter is not a virtue.

Not every Gen III Hemi has it. Before you buy anything:

The reliable check is physical, not documentary. An MDS engine has electrical connectors feeding solenoids in the valley tray. No solenoids, no MDS, no delete. The secondary check is a scan tool: an MDS-equipped PCM exposes cylinder-deactivation parameters and can log MDS solenoid circuit codes; a non-MDS calibration has neither.

Shop the platform: Gen III Hemi parts · 5.7L Hemi · 6.4L Apache / 392

Gate 2 — Is it a collapsed lifter, a solenoid, or the exhaust manifold?

Three different problems all get called "the Hemi tick," and only one of them needs a delete kit.

• Exhaust manifold bolt tick. Loudest on a cold start, quiets or disappears as the engine warms and the manifold expands, and is audible from outside the engine at the head-to-manifold seam. Broken manifold bolts are common on these engines and are cheap next to opening the valley. If the noise fades with temperature, start here.
• MDS solenoid failure. The solenoid stops commanding its lifter correctly and the PCM sets an MDS circuit or performance code. Symptoms are a rough transition in and out of MDS, a check-engine light, sometimes a tick. This is a bolt-in repair — Mopar's 53021726-series solenoid — and does not require a delete. It is a valley-cover job, not a cam job.
• Collapsed or failed MDS lifter. The tick is present hot and cold, usually rides with a misfire code on cylinder 1, 4, 6 or 7, and does not respond to an oil change or a solenoid. This is the one that needs the delete — and by the time a lifter has failed, the lobe under it needs inspecting, because a lifter that has been rocking in its bore has usually been chewing on the cam.

Diagnose in that order, because two of the three are dramatically cheaper than the third. Confirm the tick survives warm-up, confirm the misfire follows an MDS cylinder, and pull codes before committing to the teardown.

Related parts: MDS solenoids and sensors · Gaskets and seals

What a complete MDS delete kit has to include

This is where kits diverge, and it is the whole buying decision. Four items, and why each is mandatory:

A product sold as an "MDS delete kit" that contains only lifters is a lifter set. That is a legitimate thing to buy — it is exactly right for someone reusing a good stock cam and sourcing the tray separately — but it is not a complete delete, and the difference is not visible in the product title. Read the contents list, not the name.

Shop: Camshafts · Lifters and valvetrain · Valley trays and hardware

Lifters-only vs. cam-and-lifters — how to decide

The labor to reach the lifters is the labor to reach the cam. Once the intake, valley tray and front cover are off, the incremental time to also swap the camshaft is small. That one fact drives the entire decision.

Choose lifters-only (plus tray and tune) when: the lobes inspect clean, you are happy with stock power delivery, the vehicle is a daily driver or tow rig, and you want the deactivation failure mode gone with the least possible change to how it behaves. This is the correct conservative answer for most high-mileage 5.7 trucks. You keep stock idle quality, stock torque curve, factory driveability.

Choose a cam-and-lifter package when: any lobe shows wear, the engine is already apart, or you want more than stock. The MDS-delete grinds sold for these engines — COMP's 201-420-17 and the HHP delete grinds are the two most cross-shopped — are specified as non-MDS parts precisely because the delete is assumed. A cam swap also opens the valve-spring question: mild delete grinds usually live on stock springs, but meaningful lift over stock needs springs rated for it. Check the grind's spec card against the spring's rated lift rather than assuming stock springs carry over — it is grind-specific.

One caution specific to the 6.4: the Apache is a VVT engine with a cam phaser the 5.7 does not have. A 6.4 delete has to account for it — either retaining VVT with a compatible grind, or locking it out, which is a different parts list and a different calibration. Do not carry a 5.7 parts list across to a 6.4.

Shop: Valve springs · Timing components and phasers

Supplier comparison — what the market actually offers

Four suppliers cover essentially all of this category, and they occupy genuinely different positions.

There is no meaningful "best brand" here the way there is with head studs. The lifters are the part that matters, the trays are functionally equivalent, and the real differentiator is kit completeness — whether the box contains the tray and plugs, or leaves you to discover you need them at 9pm with the intake already off.

Install sequence

The order below is the sequence, not a substitute for the service manual. Torque values and the exact procedure for your year and engine come from the FSM.

1. Confirm the diagnosis. Manifold bolts and solenoid ruled out; misfire mapped to an MDS cylinder.
2. Relieve fuel pressure, disconnect the battery, drain the coolant. Intake removal opens coolant passages.
3. Remove the intake manifold and valve covers. Bag and label fasteners by location — Hemi intake bolts are not all the same length.
4. Remove the valley tray and disconnect the MDS solenoid harness.
5. Remove rockers and pushrods, keeping them in order. Anything reused goes back exactly where it came from.
6. Extract every lifter and inspect all sixteen, then inspect the cam lobes under any lifter that looks distressed. A flat or scored lobe converts this into a cam job regardless of the original plan.
7. If replacing the cam: front cover and timing set off, cam out, new cam in with assembly lube on the lobes, timing set to spec. Degree the cam if the card calls for it.
8. Install the non-MDS lifters with clean oil, then pushrods and rockers. Torque the rocker shafts in the factory sequence.
9. Install the non-MDS tray, or the stock tray with the MDS galleys plugged. Confirm every deleted oil passage is actually closed before it goes back together.
10. Reassemble intake, covers and harness with new gaskets. Retire or properly cap the unused solenoid connectors rather than leaving them loose in the valley.
11. Load the tune with MDS disabled before the first start if the cam requires it. Prime oil pressure, then break in per the cam manufacturer's procedure.
12. Verify: no MDS codes, stable hot oil pressure at idle, no misfires, no tick.

A note on the tune and on legality: MDS is a fuel-economy feature rather than an emissions-control device in the sense a catalyst or EGR valve is — but the delete is executed through a PCM calibration change, and calibration changes carry their own regulatory footprint that varies by state and by vehicle. Confirm what is permitted for your vehicle and jurisdiction before ordering a tune.

FAQ

Will an MDS delete hurt my fuel economy?

Some, and less than people expect. MDS only engages under light steady load, so the benefit it delivers shows up in highway cruising, not around town. Reported real-world penalties after a delete are small — meaningful over a lot of miles, negligible against the cost of a second lifter failure.

Can I just unplug the MDS solenoids?

No. Unplugging sets codes and does nothing about the mechanical lifters, which are the part that actually fails. It also leaves the PCM commanding deactivation events. If you want the feature off without opening the engine, a tune is the only correct half-measure — and it is a half-measure, because the two-piece lifters stay installed.

Do I have to replace all sixteen lifters, or just the eight MDS ones?

All sixteen. The eight non-MDS lifters have the same hours and heat cycles as the eight coming out, and going back in later for one of them is the entire job again. Every kit in this category is sold as a set of sixteen for exactly that reason.

Does an MDS delete require new valve springs?

Not by itself — a delete on a stock or near-stock grind normally reuses the stock springs. It becomes a spring question when the delete is paired with a performance camshaft whose lift exceeds the stock spring's rating. Match the spring to the grind's spec card, not to the delete.

Is a non-MDS valley tray required, or can I plug the stock one?

Either is legitimate. A non-MDS tray is a clean one-piece answer. Plugging the stock tray's MDS galleys with a proper plug kit reaches the same result for less money. What is not acceptable is reinstalling the stock tray with those galleys open after the solenoids come out.

My 6.4 has MDS — is the kit the same as a 5.7 kit?

No. The 6.4 Apache is VVT-equipped with a cam phaser the 5.7 does not have, so the camshaft, the phaser handling and the tune all differ. Buy a kit listed specifically for the 6.4, and confirm whether it retains or locks the phaser.

If a lifter already collapsed, do I need a new camshaft too?

Inspect before deciding. A lifter that failed early can leave its lobe serviceable; one that has been ticking for months usually has not. Since the cam is accessible at that point anyway, most shops replace it rather than gamble on a marginal lobe.

Build the parts list: Gen III Hemi parts · Camshafts · Lifters and valvetrain · Valley trays, plugs and hardware · Gaskets and seals

Fitment statements in this guide are generation-level. Confirm the exact application with the fitment tool on the product page before ordering.