The latest version of GM's 5.3L and 6.2L V8s going into the 2019 Chevrolet Silverado and GMC Sierra are able to run on just a single cylinder, as many as all eight, or just about any combination in between. It's an impressive feat of engineering that helps to make sure you have more than enough power for hauling, towing, and sweet burnouts, but that you can save as much fuel as possible when you're just cruising on the open road.

Dynamic Fuel Management can run the engine with 17 different patterns of cylinders in operation. Compare that to the last-gen Active Fuel Management that gave you a choice of four or eight. That's it. The new system mixes which cylinders are operating and which are along for the ride in ways that optimise efficiency and power delivery, and likely to eliminate the premature wear some older systems used. Here is how it works.

Not surprisingly, it starts with a computer. A lack of processing power is what ultimately killed the Cadillac V8-6-4 of the 1980s. This one monitors the gas pedal and uses that information to figure out how much torque you're looking for. It then starts running math like Sheldon Cooper on a dry erase board - without the laugh track - to figure out exactly how few cylinders are needed to give you that much torque while maximising fuel economy. It does that calculation 80 times a second, so even drivers with a double-espresso foot are covered.

So if you're putting along on the highway, it might be firing on just one cylinder. Add some throttle and you get two, little more for that hill, and you get three. Floor it because the hot light at Krispy Kreme just came on and you get all eight. Completely seamlessly.



The software and hardware that allows this comes from long-time GM supplier Delphi and controls company Tula. They call it Dynamic Skip Fire, which is a cool name but maybe sounds too techy (or too close to the C4's Cross-Fire) for GM.

The Skip part of the name refers to the fact that it can skip combustion from cylinder to cylinder. In one-cylinder mode, it's not going to just keep thumping the same piston every time, it moves through the order in the way that optimizes power, economy, and smoothness. The computer decides which cylinders to fire for each cylinder at each engine cycle. That means it can vary the pattern up to 12,000 times per minutes on a V8 at 3,000 rpm. No wonder Delphi refers to it as "cylinder deactivation technology to the theoretical limit."

The mechanical part of the system uses solenoids that are able to deactivate and reactive all 16 of the engine's hydraulic lifters. This is one time that a four-valve might actually have made the system impossible, or at least more expensive, needing double the number of solenoids.

In between the valve and the camshaft is a roller finger follower. That's basically a lifter that is controlled by oil pressure. When the engine wants the cylinder off, a solenoid cuts oil pressure to that cylinder's lifters. A hydraulic lifter with no oil is no lifter at all. It collapses, and the valves on that cylinder close. No new air gets in, the fuel injector doesn't fire, and the piston is just along for the ride. When the computer wants that cylinder back on, the solenoid opens and restores pressure. Now it's back on and running.



So why is a V8 running as a V2 or a single-cylinder more efficient? At speed, when cruising, the engine makes far more power than the 5-10 hp needed to move the truck down the highway. Basically, because you can only pull so much fuel from the mixture before it just won't burn. And even with variable valve lift, the engine still has to take in more air (and fuel) than it needs to move your truck. Close half the cylinders, you need less fuel to support combustion. Since this isn't an all or nothing system, you can save fuel in almost every driving condition, by using only the right number of cylinders. Call it EcoShrink instead of EcoBoost, since you're not adding power to a smaller engine with a turbo, you're taking displacement away from a big engine.

With the valves closed, you might think that the pistons are fighting the air trapped inside, increasing friction. And yes, the pistons are pushing against (and compressing) however much air is in there at the time. But compressed air works both ways. It fights the pistons on the way up, but pushes them back on the way down. It's not perfect, but it doesn't use much of the energy from the still-firing pistons.

GM hasn't said just how much fuel the new system will save, and that makes sense since it depends a lot on your driving style. Foot to the floor all the time, you're not going to save gas no matter what GM does. But for the rest of us, Delphi says that the technology means a 10 to 20 percent improvement in fuel economy depending on the engine. That's a seven to 15 percent reduction in CO2 emissions. That can still deliver 420 hp and 460 lb-ft of torque from the 6.2L version of the engine. Not bad.