Engine Deep Dive: Toyota Tacoma's Atkinson-Cycle V-6

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By Andy Mikonis

In the world of upgraded and redesigned pickup trucks, new vehicles normally do not get a new powertrain at the same time. This was not the case with the redesigned-for-2016 Toyota Tacoma; it received the 2GR-FKS engine — a 24-valve V-6 rated at 278 horsepower and 265 pounds-feet of torque.

Related: Sibling Rivalry: 2018 Toyota Tundra Vs. 2018 Toyota Tacoma

Though new to the Tacoma platform, it wasn't an all-new engine for Toyota. The 2GR-FKS — an Atkinson-cycle engine — is part of an engine family found in a range of other Toyota and Lexus vehicles such as the Toyota Highlander and Sienna, and Lexus GX, RX and LS. Its distinguishing characteristic is the ability of the intake valve to stay open longer than it does in other engines. That causes some of the air/fuel mixture to be pushed back into the intake manifold, allowing the engine to burn less fuel than a normal engine. However, the downside to the Atkinson cycle is that having less fuel in the piston cylinder chamber means the engine provides less power. Atkinson-cycle engines are most often paired with electric motors in hybrid vehicles to make up for the resulting power deficit. Toyota first used a variation of this engine in the 1997 Prius; now the technology is creeping into other non-hybrid vehicles, the most prominent of which is the Toyota Tacoma.

A Special Engine

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Atkinson-cycle engines originated in the 1800s and used complex mechanical linkages to adjust the length of the connecting rods; today it's done with variable valve timing. The 2GR-FKS uses Toyota's variable valve timing-intelligent wide on the intake camshaft. The controllers are actually in the hubs of the cam gears and are actuated by oil pressure through solenoid valves operated by the powertrain control module. The system can change valve timing within a range of 80 degrees. Variable valve timing-intelligent on the exhaust camshaft changes valve timing as much as 51 degrees. During cold startups, the intake valve defaults to an intermediate position, while the exhaust valve is advanced. During partial-load Atkinson operation, both valves are retarded. As the engine transitions to higher load, the intake valve timing is fully advanced and the exhaust stays retarded.

Fuel Injection

The Tacoma engine uses a fuel system called D-4S, shorthand for direct-injection four-stroke gasoline engine Superior version, which employs both direct- and port-fuel injection depending on need and load. During a cold start, the port injection is initially activated, then the direct injection phases in, delivering fuel during the end of the compression stroke. This allows the ignition timing to be retarded and the exhaust gas temperature raised for a faster warm up. As you may know, cold starts are typically when engines have the highest amount of emissions. Under light to medium loads, a varying combination of port and direct injection is used to provide the strongest, smoothest amount of power. Generally speaking, direct injection is used for high engine load ranges because of its cooling effect on the intake air, which in turn increases efficiency and reduces engine knocks.

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There are a few other features of the Atkinson-cycle engine that stand out. Even though it's not a conventional truck engine, it offers durability that truck owners appreciate. The exhaust manifolds and pipes on the 3.5-liter are stainless steel, and it uses a timing chain instead of a belt for less stretch. Additionally, the piston oil jets have a check valve to keep oil pressure from dropping when the oil level is low. Head gaskets are steel-reinforced as well.

It's also a lighter engine since the block, heads, oil pan and intake manifold are all made from aluminum, and it has composite resin head covers. Additionally, the timing chain cover is integrated with oil and cooling passages to save space and weight. Much of the exhaust system is made from lightweight stainless steel as well.

In terms of maintenance, the Tacoma V-6 comes with coolant that doesn't have to be changed until 100,000 miles; after that it must be changed at 50,000-mile increments. It also uses a serpentine belt with an automatic tensioner.

Fuel Economy

We've spent some time driving V-6 Tacomas with a 4x4 drivetrain. How does it compare with other mid-size V-6 4x4s (or all-wheel drive) with automatic transmissions in terms of EPA ratings? The 2019 Tacoma achieves an EPA rating of 18/22/20 mpg city/highway combined while the 2019 Chevrolet Colorado gets 17/24/19 and the 2019 Honda Ridgeline gets 18/25/21, putting them all in the same fuel-economy ballpark. The Tacoma bests the Colorado by 1 mpg combined but falls 2 mpg combined behind the Ridgeline. It does better across the board than the previous-generation 2015 Tacoma with the 4.0-liter V-6 and five-speed automatic, which rated 16/21/18.

We can look at PickupTrucks.com 2015 and 2016 mid-size truck Challenges for further analysis of the difference the Atkinson-cycle engine makes for the Tacoma. Even though the contests took place at different times and in locations, the testing was consistent enough to make comparisons. During fuel-economy testing, the 2015 Tacoma achieved 17.33 mpg combined empty and in 2016 it hit 19.5 for an improvement of 2.17 mpg. When loaded, the 2015 Tacoma attained 17.12 mpg combined while the 2016 got 20.8 for a 3.68 mpg increase. The 2016 model also bested the test group when loaded, but empty it came in fourth out of five competitors.

Our judges were not enthusiastic about the 2016 Tacoma's acceleration performance during that Challenge. Despite higher factory horsepower ratings, the numbers clocked against the previous generation (same driver) bore this out. The results were a wash. The 2015 got 8.44 seconds in the empty zero-to-60-mph test and 9.97 seconds in the loaded test; the 2016 took 8.59 seconds to hit 60 mph empty and 10.60 seconds loaded — so slower for both runs. The 2015 did the quarter-mile in 16.67 seconds @ 84.0 mph while empty and 17.65 seconds @ 79.5 mph loaded. The 2016 bested it empty with 16.5 seconds @ 88.1 mph and but fell behind at 17.8 seconds @ 82.5 3 mph loaded.

Final Thoughts

So, the Atkinson-cycle V-6 in the current-generation Tacoma made the mid-size pickup more competitive and solidly improved its fuel economy. The gains are subtle, but with stricter mileage and emissions requirements coming in 2025, fuel-saving technologies are likely to become more prevalent in upgraded or redesigned pickups. No doubt Toyota will have something else up its sleeve when the next-gen Tacoma and/or powertrain debuts.

More From PickupTrucks.com

Cars.com photos by Christian Lantry; manufacturer images

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Comments

OK James. Good input. More scientific formula's puts one into the realm of Bernoulli's equations. Because air is a fluid. And introducing F gets us into Newtonians 2nd law.
"most significant contributor to drag is airflow UNDER the vehicle." Seems the high speed sport's cars traditionally have been the only ones that had attention paid to the undercarriage.

Analogous in a way, or more of an aside: a Cessna 172 plane at rest with a sudden 70mph headwind would lift off the ground.

@angelo

Based on a legal national max speed of 70 mph you're discussing aero considerations within the context of speeds "less than" that number.

Try calculating the practical impact of aero on the truck that averages less than 40mph in its daily routines. Not a major factor.

@angelo

Well yes, aerodynamics is a subset of fluid dynamics.
What we are specifically discussing is the quantifiable force associated with an object moving through a fluid or fluid around a fixed object.

Fd=(1/2pu^2)CdA

As velocity (u) increases, note the exponential increase in force relative to the others.
70 mph vs 30 mph is 5.4x, without discussing the eddy currents at higher velocities which further increase drag.
Velocity is the main variable within a narrow delta u (velocity), but if we were to expand the u range, as u increases, so does the relative density of the fluid (p).

@angelo

Well yes, aerodynamics is a subset of fluid dynamics.
What we are specifically discussing is the quantifiable force associated with an object moving through a fluid or fluid around a fixed object.

Fd=(1/2pu^2)CdA

As velocity (u) increases, note the exponential increase in force relative to the others.
70 mph vs 30 mph is 5.4x, without discussing the eddy currents at higher velocities which further increase drag.
Velocity is the main variable within a narrow delta u (velocity), but if we were to expand the u range, as u increases, so does the relative density of the fluid (p).

@James
Clearly your equation quantifies it all:
70 vs 30 is 5.4x
70 vs 50 is 2.0x.
Letter A, presuming it is frontal area, is still in the equation coupled with CoeffDrag, so these variables are still in the control of front end Design Engineers.
It's just plain clear that a more aero front end may be at odds with the image a product marketer may be trying to portray with a big "tough looking brauny" front end.

Funny, on my late night run, which turned wet, I had the chance to wrestle my mind through some of these equations: F=mdv/dt=md(dx/dt)/dt, as rusty as they've become in my mind after 30 yrs. Always good to exercise the mind in this fashion.

Eddy currents, ie, non-laminar, ie turbulent air fluid flow as it try's to get from front of vehicle to back along any path. Presumably, clearly a secondary effect at low speed which becomes much more dominating at higher speeds.

Toyota Tacoma. The best. Next..........

Toyota Tacoma. The best. Next..........


Posted by: Colorado Crusher | Feb 28, 2019 2:17:32 PM


Toyota has always produced more liberal based products.

"All of that Aero discussion's irrelevant at low-speed (or no speed) situations. My truck spends more time at low speed (and no speed) conditions, so for me whether engineers can make it more efficient at 85mph is much less important than having a truck that will live to see 200k miles click over on the odometer." ---- Posted by: papajim

--- Apparently my situation is the exact opposite, only in heavy traffic is my speed below 45mph unless the posted speed limit is below 40mph. I still think it's interesting that my big mid-sized Chevy with V6 is getting the same kind of fuel mileage my little Ranger was getting... but that's beside the point. Probably the best way to relate aerodynamic drag would be to stick your hand out the window while you drive. Put your palm into the wind and see how long you can keep it out there as you accelerate to your typical driving speed. Then, lay your hand flat--edge on to the wind--and do it again... feel for yourself how much the load on your hand changes. Finally, form a fist and do it again. Quite literally, changing the shape changes how much pressure you feel on your hand.

Now, think again about the shape of the nose of your truck and its size.... and try to visualize just how much air is being displaced.

Oh, and on that old Ranger of mine; I know something wasn't right and the only thing I could conclude is that the mass-air sensor may have been either defective or somehow the airflow into and around it was obstructed. As I said before, even on hot days as long as the engine started out at air temperature, what the temp gauge would call 'cold', it ran well. But once the block was heated up, it took far longer for it to cool back down to 'cold' and the MAS simply couldn't compensate.

The guy I sold it to uses it as his daily commuter, so it tends to sit for 8-10 hours between trips. He's never noticed the issue and when considering he almost never uses first gear to accelerate, any loss of power seems to be ignored. He was ecstatic to get a practically-new 21-year-old Ranger and he's an obvious Ranger fan as he owns two other Rangers, one a 4x4 and the other a V6, both with high mileage.

Why do you think city buses are shaped like a box of crackers?

Aero does not matter at those speeds. Period. Look at the high speed trains---aero is a big deal at those speeds. Same objective (mass transit), but different speeds.

the mass-air sensor may have been either defective or somehow the airflow into and around it was obstructed. As I said before, even on hot days as long as the engine started out at air temperature, what the temp gauge would call 'cold', it ran well. But once the block was heated up, it took far longer for it to cool back down to 'cold' and the MAS simply couldn't compensate.

@Vulpine

Those sensors were awful. Most of the electronic stuff on those later 2.3s was good, but many of those sensors were manufactured in Timbuktu.

Really sad. GM had a 2.8 six cylinder back in the 1980s that was great until it got fuel injection and after years of grief it turned out that the MAP sensor was the WRONG number. It was wrong in EVERY GM catalog and parts dept. in the whole country. They fixed it and the 2.8 ran GREAT afterwards.

Ditto for the Rangers. Their 4.0 engine was the same way.

Now, regarding aero. If the vehicle is stationary or if it's not traveling at highway speeds, the aero factors are a total waste of development money and attention.

Coming from a former Toyota truck owner - this is a good engine, no doubt, but the wrong engine for a pickup. Unnecessarily techy and complex (aka expensive) with too little low end torque.

"Why do you think city buses are shaped like a box of crackers?"
--- To carry the most amount of people in the lease amount of space. At 20-30mph with stops every block or two, aerodynamics don't even play into the equation. Weight, however, does.

"Look at the high speed trains---aero is a big deal at those speeds. Same objective (mass transit), but different speeds."
--- Not exactly true. High-speed trains are built for comfort over longer distances (inter-city distances as compared to intra-city distances.) So they aren't facing the same objective at all.

I ride a train from Lorton, VA to Sanford, FL, outside of Orlando. I've done so the last two years running and that train runs at just under 70mph at speed. It's also pulled by a fairly conventional diesel locomotive and is therefore reasonably slab-nosed. The high-speed train such as the Acela Express is built to run 150mph or faster and draws its power from an overhead electric line. There's quite a difference.

However, before you say this proves your point, I would remind you of the old Pennsylvania GG1 locomotive that used to pull the later Amtrak trains under the wires. It was a much more streamlined locomotive and pulled those trains (between the multiple railroads and consolidations over the years) for roughly 40 years. The only reason they replaced them with newer was that the old GG1 was wearing out and 'modern' design was more the box cab before they realized that aerodynamics were truly important for economy. Modern diesel passenger locomotives have front ends that look more like a modern motorhome than a locomotive.

Yes, aerodynamics do count and I can guarantee that more vehicles, including trucks, will be taking a more slant-nosed, almost cab-over look compared to what we have today. Even if they're only run at 35mph. I mean, just look at what has happened to the old Econoline van... It's now called the Transit and is almost big enough to carry the old Econoline inside.



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