advanced vehicle engine with pistons in motion and cylinders firing
Firing only the cylinders you need.

Dynamic Skip Fire: On-demand cylinder deactivation.


In your pursuit of greater fuel economy and lower emissions with internal combustion engines, the keys to unlocking the gains you need can often be found in the art of refinement.

Take cylinder deactivation. Also called variable displacement, this proven method generally involves turning off half an engine’s cylinders during light usage in order to save fuel and cut emissions. While sound, the approach has its drawbacks, particularly in areas of precision, noise and vibration. To take it further, it needs a view from a new angle.

An elegant enhancement.

DSF starts purposely skipping cylinders to save you fuel when you just need a little power.

Dynamic Skip Fire (DSF®), the industry’s first fully variable engine cylinder deactivation technology, is that elegant enhancement. This next logical step in engine control is an advanced valvetrain system that combines Delphi Technologies’ cylinder deactivation hardware with proprietary software developed by our Silicon Valley partner, Tula to fire the exact number of cylinders needed to meet the driver’s request for power and torque.

If you only need 25 horsepower and one cylinder – then that’s all you get. Why fire four of eight when you don’t need that many? And, if you need more – you get more. The on-demand system is constantly adapting to changing driving conditions.

How DSF works.

DSF determines which cylinders to fire in real-time, at each firing opportunity. This is possible because it’s an integral part of our engine control strategy, where valve activation, throttle opening and ignition are optimized together. The strategy centers on a deactivation device called a roller finger follower, which essentially functions as a virtual on-off switch. The electronic control system sends a signal, via oil pressure, to this switch. When it gets the signal, it locks down the air intake and exhaust valves, preventing air flow in and exhaust out. The pistons continue to work with the captured energy, but without air there’s no combustion. When the cylinder needs to fire again, the switch re-opens the valves.

The selection of which cylinders to “skip” is made based on avoiding known resonance patterns within the engine, providing exceptional refinement. This means the problems you generally see with noise, vibration and harshness are solved.

By making a fire / no fire decision for every cylinder on every cycle, DSF takes cylinder deactivation technology to the theoretical limit. The DSF can vary the combination of cylinders firing as often as 6,000 times per minute (@3,000 rpm) on a four-cylinder engine and up to twice that on an eight.

The returns you can see with DSF:

  • Seven to 15 percent reduction in carbon-dioxide emissions, depending upon the engine.

  • Ten to 20 percent fuel economy improvement compared with conventional spark ignition engines, depending on the engine and driving conditions.

Active valve vs. deactivated valve illustration


Dynamic Skip Fire variable sequence.

Looking ahead.


In the future, Delphi Technologies and Tula will leverage DSF to help you manage exhaust levels and protect after-treatment on overrun and enhance Miller Cycle operation. DSF will even be used in advanced combustion engine concepts like gasoline compression-ignition. We will also be looking to DSF to provide you with new opportunities to optimize your combustion strategies and complement your hybridization programs.