Unboxing the 3.5L Tacomas Abilities Through the Power of Electronics
Unboxing the 3.5L Tacoma through the power of electronics...via tuning the engine and transmission. Our current progression and our upcoming development.
OVTune has now clocked year 1 of development "complete" on the new 2GR FKS platform and we have been busy at work. Over the course of the year we have combed through endless amounts of data, hex, OBD captured engine and transmission control data, user feedback, community driven development, and we are happy to say year 2 will have more in store than we could of imagined.
What we have achieved so far
Engine Dynamics - Power
When everyone thinks of a tune they think of horsepower. How much horsepower does it make? Torque? We will be the first to say horsepower was not our primary focus, but in the end making an engine more efficient usually results in better power.
We allocated a lot of time calibrating the best valve timing angles at all possible engine rpm and load scenarios. From 1000 RPM all the way to 6200 RPM and everywhere in between. The stock tune does not do this. The stock tunes primary focus is from 1000 rpm to around 3000, where Camshaft timing (VVT) is tuned for some levels of Atkinson like targets, and high amounts of advance depending on load.
The camshafts are "intelligent" by using electronically controlled phasers that move the placing of the camshaft in conjunction with the crankshaft to meet certain degrees of change from base (we will call this 0*). At 0* the camshaft would be at it's set mechanical timing (where you would put it when putting the engine together). But this is not the most efficient for when the engine is driving. The ECM, or brain that controls the engine, uses a series of tables that take engine load measurements and engine RPM and move the camshaft to different degrees. This is the basics of how VVT (variable valve timing). We took our time and mapped the entire valve timing range, and as a result found we could expand the Atkinson mode WITHOUT decreasing engine performance.
After mapping the valve timing, we spent some time in the common tuners play-field. Fueling and Ignition. Fueling is rather simple. There are general tuning "rules" that apply when you map an engine, and the rules of fuel are pretty much set in stone. Naturally aspirated engines generally like a leaner mixture, even at full throttle, say 13:1 AFR, or around 0.89 lambda. But this is a truck, it's going to be towing, off-roading, and potentially moving weight up hill causing a lot of heat under heavy load. The stock tune runs extremely rich (under 11.0 AFR.. fuel wasting rich). We made improvements by moving our targets to a leaner, yet completely safe, mixture of around 12.3 to 12.0 under full load. Part load and idle remain unchanged, the standard 1.0 lambda.
Ignition Timing was critical and proved a challenge. There are several "base" ignition maps plus multiple levels of ignition trimming features, along with knock control and knock feedback correction.. plus learned feature values. It took us a majority of the year to fine tune ignition the way we wanted, and have finally arrived as a solid ignition map which takes all pieces into account. Changes in VVT, changes to fuel octane, and more. We found that we could make nearly 25 horsepower gain, measured at the wheels, by altering ignition timing for use with 91 octane.
Our end result on a stock vehicle with larger tires
Gains measured of 22 Horsepower and 25 ft lbs
measured at the wheel on 91 octane pump gas.
Expanding Atkinson mode - Why we did this
From time to time we see people in various vehicles think that Atkinson like behavior is a hindrance to their engines overall performance. This couldn't be further from the truth in this day and age of technology. Routinely we get asked to disable, delete, minimize the valve timings Atkinson like mode. We oped for the opposite. Expand Atkinson mode and increase efficiency where-ever possible. The thing about Atkinson mode in a vehicle with intelligently controlled hardware is, there is an off switch. there is a "disable feature," it's called the accelerator pedal. During normal and light driving the valve advance will be severely reduced to allow a bleed off of cylinder filling so that a better resulting mixture can be obtained. Under light driving your engines cylinders are not completely filling with air (if they were, the throttle wouldn't do anything). There is a high amount of vacuum behind the throttle, and the amount of air that enters the intake manifold must be fraction-ed and dispersed to each cylinder. When Atkinson "mode" is enabled, the intake valves do not completely close until the piston is already moving back up to compress the air. A small amount of the air is not used and pushed back towards the intake manifold. Then the remaining air is burned and the process starts all over. How this helps with efficiency is a pretty simple concept. The force that moves the vehicle does not change (the power stroke), but the force that drives the power stroke is reduced. By reducing the force that provides the power stroke, while obtaining the same power stroke, you are getting more work done, more efficiently.
A very simple way to understand this can be seen below:
Imagine engine A and engine B.
Engine A uses 100% compression stroke, 100% power stroke. Resulting in 50 ft lbs of driving force.
Engine B uses 70% compression stroke, 100% power stroke. Resulting in 42.5 ft lbs of driving force.
So you lose 7.5 ft lbs. However the vehicle only requires 30 ft lbs of driving force to maintain it's speed. You sacrifice a small amount of power that you do not need, to create a more efficient drive.
One unanimous complaint from the community was that nobody was seeing the MPG numbers that Toyota advertises. Our test truck would never see above 17.5 mpg highway. A far cry from the 22 that Toyota advertises.
So we spent time further improving the very small range that Toyota placed for this engine to be in atkinson mode. Rather than it being in atkinson for only a fraction of load and very low RPM, we expanded atkinson like valve timing to nearly 4000 RPM and load measurements of 40%.
This resulted in a net increase of MPG of 2-3+ MPG real world measurements, backed by more than 500 tuned trucks reporting similar numbers. People started actually seeing the number "20" on their MPG dash.
And we are not even done yet. We are confident we can further expand the abilities of this cam through further fine tuning of the exhaust timing to increase efficiency even further.
But doesn't tuning and changing the valve timing mess with the emissions? Not really. Nearly all harmful emissions are happening at the first cold start up, which we also changed!, but will discuss at a later time. Several people have reported to us that they have taken their vehicles in for voluntary emissions testing and have passed.
Our tune has been independently tested and passes all of Toyotas Federal Emissions regulation standards. We will have all of this emissions data and emissions test information published soon.
Torque Dynamics - Response
The Toyota Tacoma ECM uses a new logic feature that seems to be more and more common as vehicles with electronic throttle-bodies become more and more complicated. Torque based driving control. Gone are the old days where you press down the gas pedal and expect a linear result from the engine. There is a whole new system at play, and it's all modeled around Torque. Toyota uses a complex algorithm to model what it requests from the engine based on what you tell it from the accelerator pedal. It takes vehicle speed, engine RPM, accelerator angle, steering angle, traction, wheel speed all into account.
This was one of our first places to improve. We all know the truck feels absolutely gutless and doesn't move when you tell it to. By changing the tables that control throttle opening and modifying the modeled torque tables we were able to make the Tacoma feel more like the accelerator pedal is directly connected to the engine.
Power Demand - Response
Part of that torque modeling is Power Demand modeling. What is power demand? It is basically a set of rules via tables within the ECU that means "when all things = this, and accelerator pedal = this, request x amount of torque."
We changed the 16 way dynamic Power Demand also commonly known as Driver Demand maps to give more immediate response and feedback.
Many customers have reported to us that it makes them feel more confident to drive and actually makes them feel like the truck is safer to drive. A big problem with the stock Driver Demand is that under certain conditions, especially when turning and the wheel speed measurements differ, the throttle may effectively feel "dead." This could lead to a disastrous scenario when you have to quickly make a turn, or try to turn left when their is oncoming traffic. (actually this was a big complaint)
Throttle Calibration - Response
Throttle calibration was a relatively simple process that allowed the throttle to act more like... a throttle. The stock throttle mapping is anything but linear. Our previous blog covers this in greater detail. Our calibration changes the dynamics of the throttle mapping for every driving scenario. Effectively removing the need for those "throttle fixers" or throttle modding electronics.
Torque Converter - Efficiency
Now that we have the engine running the way we want, we dived into the automatic transmission components. One of the least thought of, but critically important piece of the tuning puzzle is Toyotas mult-stage Torque Converters. This specific Torque Converter uses a 3 stage design, which has no lock status, partial slip allowance locking status, and full lock status, which is based on measure Torque nm. Full lock achievement above 200nm (in stock form). We found we were able to further increase efficiency on the highway by direct MPG measurements while also giving the truck the ability to MAINTAIN 5th and 6th gear on the highway by changing the locking control in 5th and 6th gear while alos changing the throttle limiters. By allowing a completely FULL lock above 1200 RPM in 6th gear any time the throttle is applied while also expanding the limit of throttle angle in 6th (stock tune will not let you go over 25-30% throttle in 6th...no matter what) we were able to observe better mpg and 6th gear maintaining, even at speeds as low as 60MPH. this drastically changes how the truck drives and performs on the highway.
Transmission Shifting - Efficiency
If we are being completely honest here, we can safely say the automatic transmission in the Tacoma is probably the worst feature of the truck. At least stock it is. I don't blame Toyota. From what the calibration shows, it seems they wen't "over the top" in technology to try to create a transmission that tries to learn what works best. The Transmission is controlled by a horrendous amount of tables. So many different controls it would make the average tuner scream. We're talking over 200 different shift control tables and 16+ Transmission torque models that change how the truck shifts based on vehicle speed. A nightmare for a tuner. various models for 4x4 drive mode, ECT, S mode, ect. The Tables are also progressive in nature and it seems the ECU shuffles which table it is using to find what would be the most efficient "shift." As a result.. it's as shifting disaster. At first we didn't believe the reports, but after driving our test truck on the stock tune for 250 miles to try it out, we were embarrassed at how it acted on the highway. During a 200 mile highway drive, mostly flat, 75mph we shifting from 4th to 5th to 6th to 4th to 5th to 6th at least 30-40 times in that cycle.. and we are not exaggerating. We get into 6th gear and the truck can't maintain speed, apply the accelerator and instantly goes to 4th gear where the engine tries to race and you look like an idiot on the road.
We knew this needed work, so we got to work on this right away. It took a few revisions and changing the shift tables but we have found a way to make the shift tables and transmission torque models mimic the drivers input. It results in a much better driving experience. Our changes to the shifting and transmission control results in a better drive, a transmission that acts like it should, and 6th gear that really works.
Transmission Torque control - Progression Free Driving
One of the main problems with the Tacomas transmission is the confusing torque model tables for the transmission. There are so many of them that the way the truck shifts is extremely inconsistent. You never know what roll of the dice shift pattern you will get. One day it might seem like it shifts "decent" and then the next morning it feels like the transmission broke. Unfortunately the issue is the transmission has too many "smart" features inside it.
Our transmission calibration modifies and condense these torque models to match our shift table changes so that the way the truck drives is always consistent, and the way the truck shifts never changes. This allows the truck to be one of the main things it isn't... consistent.
What we aim to achieve in 2018 and 2019
One thing all of our customers benefit from is free updates. All of our development we share with the Tacoma community and we do our best to take the communities information and opinions and use that to help develop a tune that works best.
Some things we are actively working on for future calibration releases are
Improved Transmission shifting
We spent a majority of time with the automatic transmission to improve it's shifting characteristics and are confident we have done well, but there is always room for some improvement. Our aim is to further dial in and perfect our shift patterns and torque modeling to make the Tacoma really feel alive and responsive, without racing to the higher gears or lagging behind in a lower gear.
Improvements to torque under 3500 rpm
One of the challenges with tuning this platform or any small displacement engine is increasing torque without increasing RPM. This is, to say lightly, a Camry engine put in a truck. It desperately needs more "oomph" where it does more of it's driving, and that's under 3500 RPM. The engine excels when you increase the engine RPM and it really shines when you approach 5000+ RPM, but who drives a truck like that? Not many.
Our aim is to develop hardware components, and match that with tuning to increase torque as much as possible under 3500 RPM. A tuned intake, exhaust, and camshafts are in the works. (Also force induction...........)
Improvements to 5th and 6th gear Throttle demand
The main reason the high gears suck. The throttle! We can't understand why the higher gears would have throttle limiters.. but they exist. Not only do they exist but you can feel it. When you are driving in 6th and slowly push and increase the gas pedal you can feel the truck do..nothing. There is a dead zone where the truck will do nothing until you reach a certain "demand" on the throttle and it downshifts. This big "limbo zone" of no extra throttle and no additional acceleration is why the truck dances from 4th to 6th gear. You can't maintain or accelerate in 6th, but you also can't stay in 4th on the highway (that's just obnoxious)
We will expand the throttle allowance in the higher gears to truly make them useful in all scenarios.
Refining our tune for user modifications
Modifications is always a factor when it comes to tuning, but there is a separate world when it comes to tuning trucks. Gear changes, larger tires, bigger wheels, lifts. All of this changes how the truck drives, and requires a custom touch to the calibration to make it drive as pleasantly as it would with our calibration on a stock truck.
We will begin offering custom tuning this year for highly customized trucks in need of this additional attention. We will also be gearing our R&D Tacoma with the most popular gear option so we can develop a tune specifically for these gears.