Chrysler’s Gen. III Hemi engines have been potent performers right out of the box. But that power often comes at the expense of fuel economy. So to help folks stretch their MPGs, in 2006 Mopar engineers introduced a Multiple Displacement System (or MDS, if you’re in a hurry) that deactivates some of the V8’s cylinders while under light load.
But the MDS capability can be vexing for owners looking for all-out track or towing performance, and could potentially even create some reliability issues as well, specifically concerning the engine lifters.
Hat Tip to Summit Racing Technical Experts Matt Strebler and John Jones for their contributions to this story. You can see their original article on deleting the Gen. 3 Hemi MDS here.
How to Eliminate the Multiple Displacement System in a Gen. III Hemi
Step 1: Swap The Camshaft
If you’re looking to eliminate the Gen. III Hemi MDS feature instead of simply disabling it*, the job involves replacing some key engine components, starting with the camshaft. That’s where the lineup of Summit Racing Pro Hemi Non-MDS Camshafts comes in.
* We’ll give you a few ways to disable your Hemi’s MDS system too, keep scrolling.
The Summit Racing folks are kind enough to give you the original O.E. camshaft number in the part description, so you know exactly which bumpstick to use. Even better, the cam cards all include the degrees of advance that are designed into the camshafts—so you can install the cam dot-to-dot with confidence that the valve events are correct for the application. You can see more details on each Summit Racing Pro Hemi Non-MDS Camshaft in a table at the bottom of this article.
Step 2: Swap the Lifters
While you’re replacing the camshaft, you’ll want to upgrade to non-MDS style engine lifters as well—which, if you’re reading this article, there’s a chance you may have suffered a lifter failure already. In that case, this step is mandatory anyway (just make sure the lifters are for a non-MDS application).
Step 3: Remove the MDS Solenoids & Install Block-off Plugs
Mopar Replacement offers Multiple Displacement Solenoid Plugs that go in place of your existing MDS solenoids. Simply pop them into the newly-vacant solenoid ports on your Hemi*, and you’re done with the parts-swapping facet of this job.
* Note for VVT-equipped engines: If you want to maintain VVT operation, you MUST retain the entire wiring harness for the MDS system. Once the MDS block off plugs are installed, the MDS solenoids are no longer needed. However, DO NOT cut the plugs off for the MDS solenoids or unplug the MDS harness from the main harness. Doing this will also disable the VVT.
Step 4: Turn Off the MDS System with a Tuner
Now you need to tell your Hemi’s ECU to turn off the MDS system using a capable computer programmer (or via a custom tune). This will ensure your vehicle’s computer won’t engage the MDS system once you start driving.
…And that’s that. Button everything up, close the hood, and you’re firing…
<David Caruso Glasses>
</David Caruso Glasses>
Alternative Ways to Disable the Gen. III Hemi MDS System
As alluded to above, there are a pair of ways to simply disable the Hemi’s Multiple Displacement System. Though you should be aware of a few caveats to these two options, which we’ll explain below:
MDS Shutoff Option 1: Just Turn It Off
OK, so astute readers may already know this, but you can turn off the MDS system by simply switching the vehicle’s transmission into either the Sport, Tow/Haul, or Manual shift modes.
But here’s the catch: That option resets back to normal and re-engages MDS with every key cycle—so you’ll have to make that adjustment each time you turn on the vehicle. Bummer.
More importantly, the mechanical parts are still in the engine, which means there’s still a risk of an internal component failure.
MDS Shutoff Option 2: Turn Off MDS with a Programmer
As with the final step four of the job outlined above, a quality computer program or tune can disable the MDS system and prevent it from activating. That way, you won’t have to keep turning it off whenever you hop in the driver’s seat.
But again, just turning it off means you’re keeping all of the MDS system parts in the engine—so you’re still risking a component failure and not getting the benefit of upgrading the internal parts from either a performance or reliability standpoint.
You may also appreciate our comprehensive Hemi Spec Guides too.
Summit Racing Pro Hemi Non-MDS Camshaft Part Numbers, Specs & Applications
So, ready to completely remove your Gen. III Hemi Multiple Displacement System? Well again, it starts at the cam. The good news is, Summit Racing Pro Hemi Non-MDS Camshafts are available for many popular applications for Dodge, Ram, and Jeep vehicles. And the better news is they give you the OE replacement part number for a perfect swap from your existing camshaft.
Check out the table below for more detailed specs.
Summit Racing Pro Hemi Non-MDS Camshaft Specs
OE Cam Number
|2003-07 5.7L Ram w/no VVT or MDS
|2009-21 5.7L Ram/Durango w/VVT but no MDS
|2009-21 5.7L Challenger/Charger w/VVT but no MDS
|2011-20 6.4L Challenger/Charger/Durango w/No MDS