How It Works: 2016 Toyota Tacoma's 'Atkinson' Cycle

21 Tacoma Tan 1 II

By Tim Esterdahl

Most pickup truck fans probably know the new 2016 Toyota Tacoma will feature a new 3.5-liter V-6 engine, yet that isn't the whole story. This new engine will use the "Atkinson" cycle, most notably found in the Toyota Prius. It promises to provide better fuel economy, but could potentially cause confusion among buyers. Here is what you need to know.

Typical 'Otto' Engine Cycle

Before we get to the Atkinson cycle, we should first explain that the vast majority of gasoline engines use an "Otto" engine cycle. This cycle gets its name from German inventor Nikolaus Otto and his partner, Eugen Langen, who demonstrated its use in a four-stroke model in 1876. This is the cycle most people know: intake, compression, power and exhaust. It uses fuel, air and spark plugs to fire the piston, turn the crankshaft and make the engine run.

The cycle is so popular that most people don't think of it as the Otto cycle. They merely think of it as the gasoline engine. The Otto cycle was the basis of all gasoline engines until the Prius came along.

What Is the 'Atkinson' Cycle?

Simply put, the Atkinson cycle aims to use all of the energy in the cylinder. It does this by leaving the intake valve open longer, creating a shorter compression stroke.

In the Prius engine, the net result is an effective compression ratio of 8:1, while the expansion ratio is about 13:1. This differentiation results in the engine being 12 to 14 percent more efficient than the Otto cycle in terms of power output per fuel consumed.

When a typical Otto cycle finishes, there is some ambient pressure left in the cylinder. This pressure helps to "push" the spent gases out of the cylinder into the exhaust manifold and exhaust. While this system works, it wastes energy pushing the gases out rather than harnessing the energy to eventually turn the wheels of the vehicle.

With the Atkinson cycle, once the power stroke is complete (i.e., the four cycles are done) there is almost no remaining pressure in the cylinder. This is accomplished by leaving the intake valve open for a small portion of the compression stroke. As the piston head moves downward, a new, fresh fuel mixture is pumped in. At a predetermined point in the stroke of the piston, the intake valve is shut. The net effect of this is that the power stroke is shortened.

Both power and exhaust strokes remain the same in the Otto cycle, yet the Atkinson cycle uses almost the entire length of the piston travel.

A downside to the Atkinson cycle is that you still have to get the exhaust gases out of the cylinder since you aren't using ambient pressure any longer. Early Atkinson-cycle engines had superchargers to combat this problem. However, Toyota devised a "tumble flow" intake system on the Prius to counteract the problem. This unique system uses atmospheric pressure to push the exhaust gases out.

Another downside of the Atkinson cycle is the shorter power stroke delivers a narrower rpm range. In the Prius, Toyota solved this problem with a continuously variable transmission and an electric motor. These strategies keep the engine running in the optimal range while providing a smooth driving experience.

Additionally, the Prius' intelligent variable valve timing system adjusts the intake valve timing to maximize fuel efficiency.

We know the 2016 Tacoma will have Toyota's D-4S technology, which features direct and port fuel injection. This system is currently used on the Scion FR-S and Subaru BR-Z. It "combines injectors that inject fuel at high pressure directly into the cylinders, together with conventional injectors, injecting fuel into the intake ports," according to Toyota. The two systems turn on and off depending on engine speed.

The system also injects fuel during startup and at certain load points to improve combustion stability without using a restrictive intake port design that increases tumble flow.

What Does This Mean for Truck Buyers?

The Atkinson cycle is more efficient than the Otto cycle, so the 2016 Tacoma's new engine will offer better fuel economy than other conventional V-6 engines without having to resort to turbochargers or diesel fuel.

While the Atkinson cycle does a great job of maximizing fuel economy in the Prius, it remains to be seen how the cycle will work in a pickup truck with very different duty cycles. Highway and empty-bed fuel economy will be improved, but we really don't know how towing or payload hauling will be impacted. We assume Toyota has this figured out and that's why it has taken so long to bring the Atkinson cycle to other vehicles (the Prius first went on sale in 1997).

In the end, the new 3.5-liter Atkinson-cycle V-6-powered Tacoma with a new six-speed automatic transmission and new rear differential is likely to have best-in-class fuel economy. How well it can handle pickup truck duty remains to be answered. photos by Evan Sears


20 Tacoma Lim 4 II





My opinion: variable valve timing offers a more relevant approach than the finicky ACE (atkinson cycle engine). The ACE is a bit like the variable displacement systems that work well only in situations where the vehicle is cruising under light load.

The advantage, as Toyota folks are quick to point out, is that it delivers similar fuel economy improvements available through other means (turbo), but without the concerns of wear and fatigue more common to some turbo systems.

Having been around giant marine engines aboard freighters in my youth I can testify to the durability of turbo designs. Likewise for other diesel applications such as over-the-road trucking, etc.

Pumping losses constitute a considerable part of the wasted energy in Otto cycle engines, but the reliable Otto runs happily under load in a variety of situations that would be out of the question with an ACE system motor.

None of this will be very interesting, except maybe as an engineering exercise, if crude oil prices remain low during the next five or ten years.

The current phase of commodity pricing in oil and gasoline reminds me of the early 1980s. We enjoyed about fifteen years of cheap gas beginning in those days that lasted until the later 1990s. Gasoline at less than 1.75 per gallon (reg. unleaded) may be on tap soon.

Also the longer stroke equates to faster piston speed, which means more wear and probably lower rpm. Not a good engine for a truck, but maybe OK for a tacoma.

You know, the way I read this description, it sounds like the truck will run Atkinson for empty and light-load economy while reverting to Otto for heavier loads. Why else have two separate intake systems? The VVT should make such a switchover pretty easy as per description the computer will easily sense the load on the engine to add additional fuel as needed. Granted it's a complex system that could have far too many points of failure, but when it works, it could be exactly what Toyota is looking for.

You do realize that this is nothing new or earth shattering. Any engine with vvt does this to a varying degree; depends on the vct range. Ford does this on the 5.0l, gm on their 3.6l v6, etc. Also you do not want the engine stuck on Atkinson, or it would be a dog. You take a hit on voleff; thus lowering torque output. Only need Atkinson cruising or at light load.

The one thing this article fails to mention, is that Toyota's Atkinson cycle engines and especially it's D4-S Direct Injection system (port & direct injection technology) are trickle down technology from it's LEXUS division as well.

Lexus is the most reliable vehicle brand in the world often consistently ranking number 1 or 2 in reliability rankings year in and year out. When Toyota builds Lexus cars, the plant that builds them has even tighter tolerances and requirements for quality/attention to detail than a Toyota plant using Lean manufacturing techniques which Toyota invented! So if Toyota decides to put a technology or type of engine behind a Lexus it's because it has gone through the ringer in reliability and quality testing. Rest assured the technology behind this new Tacoma engine will stand the test of time and I'm sure it will have solid power ratings along with improved mileage over the current 4.0 liter V6.

This is not an atkinson engine nor an "atkinson-like" engine. Its a standard otto-cyle engine with VVT which they have engineered to leave the exhaust valves open slightly longer. This can only help so much, since the static compression ratio is *way* too low to really take advantage of major fuel economy gains.

Just when GM thought they got the midsize market locked down. Back to the drawing board GM.

I still remember when everyone complained how VVT don't belong in truck engines examples like the tundra. Guess what... GM, Ford and Ram all have VVT now in their engines.

Longer-stroke engines used to be very popular for truck engines, and the ACE utilizes a longer stroke and, I presume, a heavier flywheel.

And with computer management of the spark, injection and valves, we're one step closer to a fully-computerized car.

All this is great until the"computer" has a bad hair day, and then we, the drivers, are up the creek without a paddle. Or more famously, dead on the road without an engine.

Hell, if things get this complicated, why not put in a 12-rotor Wankel and at least have something to show for all the glitz.

Fuel economy in a truck!? Why? We have plenty of gas and are swimming in oil for at least the next 200 years.

If a person has to worry about the cost of gasoline, they ought not to buy a truck! A Prius, maybe. But not a truck.

Marketing spin nothing more.
With the low redline of this variant of the 2gr-fse V6, GM's new Canyon/Colorado are still the most powerful 'compact' pickups.
And GM should install the 10 speed automatic into the C-C twin for '17 M.Y.

Too bad all 300hp+ of that GM V6 is above 6000rpm. It has no guts in the usable range of 1500-3000.

@Highdesert cat--Oil prices will not stay low, eventually they will go up. Also the new higher fuel standards are forcing manufacturers to use whatever technology they can--aluminum bodies, shudder grills, direct injection, and a host of other things.

@Jeff S

If you have a crystal ball then I know some commodities brokers who will hire you on the spot.

The dollar has gained ground on all but a few of the world's currencies in recent months and gas prices came down a lot because of it. Europe is also in a very down time; this week the dollar and the Euro were trading 1:1

All of this points to a down economy for now and soft demand accompanied by a stronger dollar. Equals the kind of cheap gas we had in the 1980s and 90s.

Supply and demand will impact oil and gas prices in the near term but it's the currency, i.e., the long term strength of the dollar that determines oil prices over extended periods of time.

King Dollar is here.

@papa jim--Eventually oil prices will go up, you don't need a crystal ball to predict that. As the price drops there will be producers that will cut production. As long as a producer is making money they will continue to produce and hope that increased volume will make up for the lower price, but if the price of oil falls low enough there will be a cut in production and some producers will either go out of business or get bought up by the competition. This is similar to the 80's. The Saudi's have not cut production and some of the reason for that is that they are trying to shake out the competition from the Canada and the US. As for the long term strength of the dollar, the dollar is one of the strongest World currencies but then that is not saying much because Europe is in a financial mess and China is having its own financial crisis. The dollar itself is based on the good faith and credit of the US Government which is itself not reassuring. For the foreseeable future we will have lower oil prices but just how long is anyone's guess.

@uh huh
It is a naturally aspirated gasoline engine, not turbocharged diesel.
You need cylinder filling + revs to make power.
and if Toyota's economy variant only makes 270hp, 255ft-lbs (with the same 94mm cylinder bore as GM)
GM has the joint Ford-GM 10 speed, which needs to be connected ASAP, '17 M.Y.
And this 'usuable range', what nonsense. You are supposed to rev it 3000-4500rpm.

I don't know if a straight Atkinson cycle is great for a pickup or high performance but Toyota must.

Interesting enough the Lexus RC-F does it a little different from what was said here as it is Atkinson cycle and Otto cycle basically. It features the D4S, higher compression ratio and the high flow tumble intake mentioned above. It also has something not mentioned here which is the more advanced vvt system that works well with the Atkinson cycle and addresses the narrow rev range. Instead of Dual VVT-i it uses VVT-ie which according to Toyota expands the area of operation "A new intake camshaft profile increases valve lift and suits the Atkinson cycle, while improvements to the electronic VVT-iE system have expanded its range of operation for increased fuel economy and performance." "Lexus redesigned the VVT-iE (Variable Valve Timing-intelligent Electric motor) technology to extend the range of inlet camshaft timing adjustment for the Atkinson cycle. The instant more power is called for, the engine switches to the Otto cycle." In theory that seems like it would work well for a pickup as it would be Atkinson cycle under no load and Otto cycle under load. That technology is supposed to be headed to other vehicles as well.

Just a clarification, Toyota did not invent lean manufacturing... Henry Ford was the one that started using this methodology. Toyota later adopted this approach to manufacturing.

The engine I have is fine 4.0. Just give me 40 or so more horsepower, or maybe a small v8 in the 275 hp region. Maybe you could revive the old 327 chevy engine, a real winner.

William Edwards Deming


Look up that name because you've obviously never heard of him. Mr Deming's innovations (along with those of Eli Goldratt later on) led to the development of Lean, not Henry Ford.

Mr Ford advanced the practice of repetitive systems and mass produced common platforms, but Mr Deming's ideas and the philosophy of Eliyahu M Goldratt led to Lean Manufacturing.

Not Mr Ford. Mr Ford's practices were quite the opposite of lean.

Look it up.

papa Jim... I did not say that Henry Ford invented it... It was, as you mentioned, started by Mr. Deming.

I just get tired of people thinking that the Japanese invented Lean when it was an American that did it. What Toyota did was to effectively adopt it.

When you're a hammer, the world is a nail. I'm underwhelmed with the Atkinson cycle. When my wife's Prius' main battery is low you can feel the true gutless heart of the engine. I guess we'll see how this all pans out but I don't have a good feeling.

Maybe they'll offer an Atkinson engine next for the Tundra.

Good god there are so many incorrect comments here u could never spend enough time to correct it!!!!

TPS toyota production system is the worlds most studied production system because it's that much better than all systems before it and all auto manufacturers have adopted much of it.....

Dual VVT-i exists on this 3.5 and Atkinson cycle is turned on and off by extreme use of vvti to create Atkinson cycle. This can be turned on and off very quickly so as your under light throttle it will use Atkinson.

Everyone should stop drinkin the hater Aide!

I doubt it is a true atkinson cycle, meaning the power stroke is longer. The atkinson also had all 4 strokes happen in 1 revolution. Smoke and mirrors.

Only you drive at 3000-4500rpm. A mast majority of people out there and me personal don't drive in that range expect for firm acceleration. My truck spends most of its life 1500-2000rpm.

Tim Esterdahl

Thanks for the basic explanations on the new Tacoma. The “only” completely new truck at this year’s show.

Unfortunately we have reached a day and age where the masses believe virtually any of the marketing hype thrown at them and they continue to fall for it hook line and sinker.

After 24 months of growth rate decline at Ford, in the so called booming economy; their solution in lieu of solving EcoBoost failures has been a major “marketing” shuffle with top management. Ram and GM are continually plague with their MDS/AFE problems (and others) while the EU will print all the money Fiat requires, the same still holds true for GM, the Fed will give them anything they want and continue to print for them today. They never have to make a profit again.

Toyota has taken a completely different approach. Build trucks that actually work and let the owners do the marketing for them. Slow, Steady, and Proven.

@Randy, I would applaud some of your viewpoints but throwing Ford, Fiat and GM into the same "bucket" so to speak is a bit extreme.

Each corporation is facing different challenges in my opinion and deserve a different bucket of their own.

Fully and whole heartedly agree with your viewpoint re the European Central Bank's continued foolishness--even worse than what we suffer through with the Fed. Absent the EU's numbnuts in government and banking, the US dollar would not be King Dollar today.

Sometimes you don't have to be the fastest runner to avoid the tiger, just don't be the slowest. The EU is the slowpoke these days--let the tiger eat their lunch.

@uh huh: Obviously neither GM nor Toyota have the mid-size market locked down. I was hoping for a more S-10-sized truck rather than a legacy full-size truck and as a result, despite my former interest in the Colorado, I didn't buy one--just too bloomin' big!

I keep hoping.

That's interesting.

I am looking forward to how it plays out.

The importance of a midsized/pretender truck having real truck capabilities or a real truck engine are very much 2ndary to the small niche they fill (people who want to think they have a truck but don't really need a truck). The mileage and how well it launches from a stop light when next to another little truck are far more important to the vast majority of its clientel.

Its great to see modern automotive technologies and engineering finally make its way into the truck world (even for these little pretend trucks). All these technologies which have been common for decades in Europe finally making it here. High output/small displacement highly efficient engines, the implementation of DI, Vari Timing, DOHC, Turbos, Diesels, modern materials, all should be as common in trucks as cars. The death of drum brakes is LONG over due. The bad news is costs will continue to rise but they had been rising anyway as more truck buyers (both the ones with and without work to do) demand more performance (in EVERY category) and luxury. For better or worse. The manufacturers are only too happy tack on more and more as the profits and stickers rise and rise. Its the natural order until some kind of tipping point is finally reached.

@uh huh
You are supposed to accelerate with engine speed. There is far more variability of power there. That is why there are transmissions.
There is less than a 10hp difference between the 3.6 & GM 4.3 'truck' V6 at 2,000rpm
And unless you are using the ManuMatic interface, you can't access full throttle at that engine speed.

The article is a little incorrect- the inatake an compression strokes are shorter, the POWER stroke is longer- makimizing thermal efficiency.
Longer/shorter is with respect to duration, not stroke. The engine ins a familliar 2GR, which has the same bore as the 4l V6 (3.7"), with a shorter stroke).
Highdesercat- everything that happens under the hood of EVERY new truck is computer controlled.Everything.
George_C- In other applications this engine has a 6400rpm redline (hardly low) and makes 305hp.the same as the 3.6 in the GM midsize truck. And yes, I've seen that truck in the Mr Truck tow test- VERY IMPRESSIVE. The Toyota should have about as much power, just as many gears, and if the 2015 model is any indication, will weigh a bit less than the GM.

One thing we don't know is will this engine utilize Toyota's VVT-iW, that is found on the Lexus NX 200? The "W" in VVT-iW stands for wide. Toyota states that utilizing VVT-iW allows the engine to operate in Otto cycle or Atkinson cycle depending on engine load.

In my opinion this would be the best option for the 3.5 liter V6 in the Tacoma. The truck would deliver great fuel economy for commuting and good hp & torque when hauling/ trailering.

@Frank- Toyota has come out and said that it will operate in Atkinson AND Otto cycles, so, yeah. More likely than not.

@Mr Knowitall
Look at the pictures. This has a 500 rpm lower redline. The 2gr-fse has a 6500+ redline (usually 6600 limiter)
285hp 265ft-lbs should be the top of the estimate for this engine.
GM has a 8/10 speed ready to go for their LFX engine.
Why didn't Toyota connect to an Aisin 8 speed?
4.85, 2.84, 1.86, 1.44, 1.22, 1, 0.82, 0.67 R 3.83
That extra 20% ratio spread over GM's 6L50 transmission would more than make up for the reduced engine power.

This is a recent shot of the New 2015 Toyota Hilux being tested in Australia. It shows how much it differed from the Tacoma

It was Random Olds that first used the assembly line to make cars, but Henry Ford improved on it. Deming did the Time and Motion studies and increased the efficiency of assembly lines. The Japanese auto manufacturers were disciples and held Deming's principles in the highest regard following them --this is what made Toyota into one of the most efficient manufacturers.

Everyone who has worked for Toyota, raise their hand. That's what I thought. YOU ARE NOT SMARTER THAN THEY ARE!! Be quiet.

It's Ransom Olds.

Why doesn't toyota make the 275hp 4.0 that's in the 2015 4 runner an option in the Tacoma.

So, a longer stroke...and trying to get more power from less RPM of the Engine. I get that - for an Automobile. From a Truck - another story. I agree that Turbocharging is NOT the way to go. But, a longer stroke followed by a short 'intake' (or should I say a comparable intake volume) as compared with OTTO style Engine doesn't convince me of any improvements unless you drive empty on the freeway 95% of the time...and I guess the majority of us do that, don't we???
Just not convinced this is a big deal...don't want any VW 'shenanigans' reported.... :-)

I work for a Toyota Dealership and just got back from Tacoma training.

I see a lot of people are confused by how this engine will work. This is another amazing Toyota engineering feat.

The Tacoma will only utilize the Atkinson Cycle when cruising (highway/interstate for example) and revert to the normal cycle it has always used for acceleration and pulling conditions. Best of both worlds....NICE

While this article is interesting, the comments are fascinating. Just reading through the debate here has taught me a lot about the new engine. Very important for someone like me looking to upgrade from my 2011 TRD offroad... 4.0 and manual (yes, manual) transmission. Thanks guys.

As an aside, a manual transmission is not offered in the "build your own" Tacoma section on Toyota's website. I nearly had a heart attack, but the dealer grudgingly assured me that it can be ordered after I told him I WILL NOT buy their "offroad" truck with an automatic tranny.

This is nothing new. Look at the cam card for just about any engine and you'll see that the intake valve doesn't close at BDC. The air charge has weight to it, leaving the valve open longer allows more air into the cylinder. Higher compression ratio means the decreased time on compression is negated. This has been around for a long time. Direct injection means that the engine is less likely to experience detonation because the fuel isn't injected until it's time to fire the spark plug. That, at least, is new to gasoline engines.

This is not an Atkinson cycle engine this is an Otto cycle engine with VVT.

An Atkinson cycle engine, the crankshaft turns 360 degrees for a complete intake, compression, combustion and exhaust strokes.

An Otto cycle engine, must turn 720 degrees to complete all 4 strokes, previously mentioned.

I bought a 2016 Tocoma TRD with the the 6 cyl engine. I have noticed less power on the interstate hills in 6th standard gear. at times I need to downshift to 5th gear. My 2012 Toyota TRD 6th speed standard had better power on the interstates hills in West Virginia. I still like the truck.

Given the improvements, how is it possible that on the Toyota website the mpg for the Tacoma 2016 is 19/24 and for the 2015 is 21/25?
It appears to be a downgrade rather than an improvement. #bringback2015

the only "small" truck anymore is the Frontier. Sad but true. Everything just keeps getting bigger!

Well I know this is an old article, but was looking for information, and understanding, I purchased a new 2016 Toacoma about 6 months ago. What I can say about this is in normal driving, empty truck I routinely see 27-28 MPG running on the highway at 65-70. Acceleration is a bit sluggish, but if you need to put you foot in it is more than adequate.

I also routinely tow a 3200 pound trailer, selecting ECT power with a switch in the cab does 2 things. It changes the shift points to allow the engine to turn up a bit more for better performance, and also shifts the valve timing back to a standard Otto cycle. There is plenty of power to tow this weight, while getting 16-17 MPG.

If you leave the truck in ECT power when driving empty, performance is really good, however your fuel economy drops to about 23 MPG on the highway.

The transmission is always busy, with the double overdrive (5th and 6th gear) it frequently shifts between 6th and 5th on even minor hills, you just get used to it.

I really think it's the best of both worlds, economy, and power when needed.

"The Atkinson cycle is more efficient than the Otto cycle, so the 2016 Tacoma's new engine will offer better fuel economy than other conventional V-6 engines"
Turns out this isn't true.
I read a comparison article of the Taco and the new Chv Colorado(gas V6) in either MT or C&D, and they reported their observed fuel mileage as being the same for both trucks. Mind you, the Colorado also produces more power, and when you look on, you see that in the 'real' world, the Colorado actually gets better mileage than the Tacoma, and it's 'more efficient' Atkinson cycle motor.
Yay Toyota!

I have the 2016 new v-6 and it has so much power
That I have to keep a light foot on the gas pedal. As far as gas milage it's great at over 28 around town rushing everywhere and close to 35 to 40 on highway. I'm so glad I got this truck. 4x4 crew cab long bed, automatic tranny. You probably don't believe me, but it' s true and I can hardly believe it. I have a 1997 4runner v6 auto, what a pig on gas, a real workhorse, but really gets poor mileage. I kept it because it's so reliable and will almost climb up a wall with a heavy load and does it with no problem. Pick- up needs tailgate down or off to get away from the air drag, but that is all. I had a 1996 dodge ram 318 v-8 posi rear and it honestly got better milage than the Toyota does, but truck had so many problems I got rid of it, only good thing was ride as the faster you drove the smoother the ride, but wife would not drive it as it was hard to park or get in and out of shopping cenerts easily. Well for what it is worth get a Toyota or and vehicle with this engine and the tranny you want and you will always be very happy, if I had the funds I would buy an other for taking deep into the forest or desert . get going asap and let me know how you are doing, I guarantee you will be thrilled. Happy driving or should I say flying, also gets a great ride on highway, but city it' a bit stiff in any case you will only come out on top.

Why does the 3.5v6 only get 1.3 more miles to a gallon then the 4.0 since it's suppose to be better. My 2016 has a loss of power uphill. You constantly have to either downshift or stomp the accelerator. Most of the time the transmission want down shift on its on. My tacoma has 30,000 miles on it and it blows black soot out the exhaust on to body panel. Must be that spent unused gas.

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