General Motors and Fiat Chrysler have used cylinder deactivation (GM calls it active fuel management) in cam-in-block V-8 engines for many years. It’s fairly easy to do with hydraulically pressurized pushrods and depending on how often and how long the vehicle can operate on half of its eight cylinders, it does save fuel. Honda has done it with overhead-cam V-6s by sliding the cams laterally between normal and zero-lift lobes.
Now GM is using a different technique to make the all-new V-6 its first with AFM. Not unlike how pushrods are deactivated in OHV engines, two of its roller finger followers (for the No. 2 and No. 5 cylinder intakes) are hydraulically pressurized or depressurized, which lets them either ride on the cam lobe or absorb the lobe input, without activating the valve.
This is one of several key innovations that help make the new 3.6L as good as it is in the ’16 Cadillac ATS, CTS, XT5 and Chevrolet Camaro, ’17 GMC Acadia and soon a variety of other models.
It’s very close in displacement to the 2008 and 2009 Wards 10 Best Engines award-winning “High-Feature” V-6 it eventually will put out to pasture. The new engine does have a slightly larger bore and slightly longer stroke, but it rounds out to 3.6L like the older, smaller version. Even so, the only parts the two engines share are hydraulic valve lash adjusters.
The naturally aspirated version spins out 335 hp and 284 lb.-ft (385 Nm) of torque, 14 hp and 9 lb.-ft. (12 Nm) better than the old 3.6L, with 20/30 mpg (11.8-7.8 L/100 km) city/highway EPA economy in the rear-drive ATS, up to 9% better. And a 404-hp 3.0L twin-turbo version exclusive to the ’16 Cadillac CT6 provides 18/26 mpg (13-9.0 L/100 km).
“The 3.6 delivers the kind of power and lusty exhaust note you associate with a V-8, for the price of a V-6,” says WardsAuto editor Drew Winter. “Plus it’s loaded with advanced technology.” The WardsAuto judges saw better than 25 mpg (9.4 L/100 km) during daily driving in a rear-wheel-drive ATS automatic and close to that in a Camaro 6-speed manual.
“The fact that a few editors needed to pop the hood or look at the Monroney to clarify which powerplant was spinning the Camaro’s wheels speaks volumes about the all-new 3.6L all-aluminum V-6."
But perhaps most impressive is its world-class refinement.
“It was designed for premium products,” says Dave Muscaro, GM global chief engineer-V-6 Engines. “So we set the mission early to be segment-leading in refinement. NVH is very important in this class of vehicle, and with a DOHC V engine with all the timing gear, you have to spend a lot of time on that. We even have cushion rings on the gear teeth for the cam phasers and the crankshaft.”
Roller Timing Chain Reduces Noise
GM’s new V-6 (codenamed LGX) uses a roller timing chain, which wears better than a “silent” chain but can be noisier, so the team spent a lot of time working on the sprockets and chain dynamics to reduce noise.
“The sprockets on the cam phasers are non-round,” (and) “actually out of phase with what the chain dynamics want to do, which drops the chain load 40% to 50% compared to the current production engine,” Muscaro says. And the rubber cushions on those sprockets let their teeth land softly, while considerable noise-reduction work also went into the chain-drive dampers.
“We had many blind listening parties,” he says. “Our noise engineers set up engines with different hardware content and combinations, recorded them on our anechoic dynamometers and coded them, but did not tell us what they were because we didn’t want any bias. We listened to them, evaluated them, made comments and made selections, then pulled the curtain back to see what our selections were.”
One feature that may be an industry first is targeted cooling.
“Typically, coolant flows from the front of a V engine through the block to the back, then back through the heads and out so coolant on the back cylinders is a different temperature than coolant on the front cylinders because it picks up heat as it traverses,” Muscaro says.
“But in this engine, with a header going down both sides of the block that releases water up through the heads, we run water in parallel across the heads and combustion chambers, then out into the V of the engine.
“The orifices in the block channel that allow coolant to go up into the heads are sized for the various coolant pressures and RPMs that the engine will see, so we get near-equivalent flow across all cylinders,” he says.
This system extracts heat more efficiently than conventional series-flow cooling systems and contributes to higher fuel efficiency by providing faster warm-up and enabling use of a smaller water pump because it reduces the amount of water flow needed to properly cool the engine.
Another key feature is intermediate-park phasers on all four overhead cams.
“Typically, cam phasers are parked all the way at one end of their travel, or the other,” Muscaro says. “But we park them in the middle to optimize emissions performance and startability, since this engine (except in the Camaro) has stop/start. Being able to retard or advance from that park position enables us to optimize performance and fuel economy, and the feel of the engine on restart.”
Other state-of-the-art technologies include high-pressure 2,900 psi (200 bar) direct fuel injection, a variable-displacement 2-stage oil pump that minimizes oil flow at lower engine speeds where higher flow isn’t needed, and a high-efficiency combustion system with high-dilution tolerances carefully designed and developed to extract the maximum amount of energy out of each milligram of fuel.
Like all engines, this V-6 will have to get more fuel efficient as federal fuel-economy rules tighten. One way to accomplish that, Muscaro says, is finding ways to increase the amount of time the engine operates in 4-cylinder mode.
“When you put an AFM engine into a vehicle,” he says, “the challenge is to maximize the use of it.”
“We’re pretty happy with what we have right now, but certainly there are items that can be improved in any design, and there are things we’re looking at for the future.”
