A New GM DOD Patent Could Finally Fix Modern V8’s Biggest Problem
Merely uttering the letters DOD, AFM, or DFM to a GM guy, and you can watch them scoff and wince at the thought of a failure-prone system to make V8s run on just four cylinders that inevitably fails and costs thousands to repair. GM introduced this system on their V8 engines back in 2005, and it quickly turned the famous LS’s reputation sour among the GM fan base. However, with new V8s currently underway, it appears that a new GM DOD (Displacement On Demand) system may be on the horizon.
A New Approach To Cylinder Deactivation
General Motors has submitted a new patent application detailing a variable displacement valvetrain system designed to deactivate engine cylinders using rocker shaft oil routing and internal insert sleeves instead of collapsible lifters like the previous AFM and DFM systems. The new GM DOD system was filed with the United States Patent and Trademark Office (patent number US 2025/0382903 A1) on June 17, 2024, and published on December 18, 2025. This filing credits several U.S.-based engineers as inventors, including Anteo C. Opipari, Paul Austin, Rolando Huerta Ortiz, and Brian J. Warner.
The patented new GM DOD system is intended for engines that use rocker arms and pushrods, making it well-suited for overhead valve configurations, as we will see in the upcoming 6th-gen small-block V8 that will debut in the C8 Grand Sport and eventually in the upcoming Silverado and Sierra half-ton trucks. It uses precisely controlled hydraulic pressure from the engine’s oil system to selectively disable valve operation on specific cylinders, much like the previous DOD systems.
How The Rocker Shaft–Based System Works
At the core of the system is a rocker shaft mounted to the cylinder heads that features an internal oil passage. An oil control valve is attached directly to the rocker shaft and communicates with this internal bore. Multiple rocker arms are mounted along the shaft, each linking a pushrod on one side to a valve stem on the other. Select rocker arms incorporate a spring lock mechanism positioned at the pushrod interface.
Under normal driving conditions, the rocker arms operate conventionally, transferring motion from the pushrod to open and close the intake and exhaust valves. When cylinder deactivation is commanded, pressurized oil is routed through the rocker shaft and into an insert sleeve located within the shaft’s internal bore. This sleeve contains dedicated feed ports and pockets that channel hydraulic fluid from the oil control valve to the spring lock unit.
Once high-pressure oil reaches the spring lock mechanism, it disengages the rocker arm from the pushrod. With the mechanical link broken, the intake and exhaust valves remain closed. By halting valve movement, the system deactivates the cylinder, reducing pumping losses and improving overall efficiency without altering the rest of the valve train.
Why This Design Could Be A Game Changer for Enthusiasts
This new GM DOD system effectively takes the old AFM and DFM systems and moves them to the much easier to access and service rocker arm area, not the lifter area underneath the cylinder heads. To keep V8s in our performance cars and trucks, manufacturers have to do whatever they can to keep the EPA happy with emissions and MPG regulations. We certainly hope this system makes it to production, because it will make it easier and much cheaper for us to delete it when it comes time for a cam swap.
