OrangeVirus Tuning Development Blog: Toyota Tundra 5.7L
OrangeVirus Tuning plans to add another vehicle to our tuning lineup. The Toyota Tundra. Many requests have been made from the community for us to develop a tuning option and calibration for these trucks, and so we have started development.
The Toyota Tundra 5.7L utilizes the Toyota 3UR-FE 5.7L Engine with Dual VVT-i (intelligent, which the ECU controls). With exception of Lexuses "F" series performance cars, this engine is one of Toyotas top performers, one of Toyota's' most powerful engines.
Lets not get ahead of ourselves though, the 3UR-FE makes great torque but a measly 381HP on the stock tune. Compare this to the lexus 2UR-GSE in the RCF which makes 467HP and 373ft lbs leaves you asking..what the heck went wrong? Well for one the 3UR-FE is a workhorse engine, built for torque and it does that just fine. But the power numbers really don't represent what this 5.7L engine can do.
Part of the problem is that the stock tune is meant to run on 87 octane fuel. The 3UR-FE has 10.2:1 Compression, 94mm bore and 102mm stroke. The engine uses a fully forged crankshaft with a torsional damper. With the guidance of tuned valve timing, there is a potential range of 90* (crankshaft timing) for valve overlap. The Intake Valve timing is at maximum retard unless certain conditions are met that allow the ECU to advance the intake valve.
What all of this means is that the engine has all the necessary recipes to make more power, with the main limiting factor being the tune. That shouldn't be a problem much longer.
So lets begin on a basic run down of a few controls in the ECM, and some things we plan to work on with tuning.
First, the VVT System. We have tuned and calibrated some of the most complex Valve timing systems ever (thanks Nissan) and we can say that without a doubt proper valve timing is where you can find the most improvements. Sure you can add ignition, lean out fuel and you'll make something. But Valve timing + proper ignition and safe AFR equals more increases safely.
So lets take a look at the stock VVT maps.
Toyota gives us tuners a lot of room to play with. The nice part is that the camshafts can be activated at low loads. What we know from calibrating other high compression dual VVT engines is that you can manipulate valve timing in the low load valve timing to make noticeable increases in MPG. Retarding the Intake valve timing while advancing the exhaust allows us to better control cylinder volumetrics (filling). By doing so, we reduce overlap and increase safe torque. Not only does this allow for better MPG, but it creates lower EGTs and allows for higher ignition advance which results in more efficient burns. Thanks Toyota for giving us so much room to manipulate the cams within the realms of the stock tables. A representation of the Tundra VVT Tables are below:
Second to that, the valve timing target is controlled by RPM and calculated engine load, which is adjusted by the ECM "on the fly." Which means that we can utilize whichever camshaft degree we want (within the realm of physical limitation) at any RPM and engine load. So we can maximize low end valve timing, and as soon as you step on the pedal the car recognizes this, engine load increases and valve timing changes in coordination with that.
This allows us to advance both camshafts in low RPM and high load, which brings more torque. The Valve timing target will increase or decrease dependent upon RPM and engine load, allowing us to reduce valve timing as RPM rises, bringing more mid range, and retard valve timing as we approach higher RPM, giving us the overlap necessary to produce the "scavenging" effect, maximizing top end gains.
Now ignition timing.
The stock Toyota ECU uses 8 bit values for a majority of their tables, and as such they do not represent real world values until they are ran through a function or algorithm to produce the real world result. Regardless of showing the actual number, we can tell you that the stock ignition timing is abysmal. 10.2:1 compression with 87 octane? yep, no ignition. increasing only ignition and running 91 octane would be a big benefit to this engine.
The ignition advance strategy is nothing out of the ordinary from what we have seen with other Toyota ECUs. They run Ignition maps for idle, low load, high load, and safe maps (and a few redundant maps). One thing we have noticed is that Toyota likes to run really high ignition advance at low load. This is great, no concern or objection there. But what we do object to is the single digit or even negative number we see at full throttle.
The image below has 3 Ignition maps pulled from a Toyota TRD Supercharged tune.
The first is the main target map under "normal" conditions. The second is an alternate map for safer conditions, and the third one is.. what?? Toyota TRD tune has raised the high load ignition on one of the maps inside the ECU so greatly it forces the ECUs code to ignore it in high load, effectively shutting off certain ignition maps. This isn't a problem, but it's the first time we have ever seen an ignition map look like this. It's shocking. If this map was ever used as an actual ignition target, you'd be running nearly 80* ignition (limited to 40*) near the rev limit, with a supercharger. Yikes! Before anyone freaks out, Toyota TRD did this for a very specific reason, and it is related to safety. So do not think the tune has a problem.
The Toyota Tundras ECM uses similar fueling strategies as any other toyota ECU. Base closed loop enrichment for cold / warm engine status, main closed loop enrichment, and open loop enrichment. Open loop enrichment is for part load and full load. The ECU also uses a strategy that reads the voltage from the MAF sensor and converts this to fuel duty. As you approach the limit of the MAF sensor, fuel duty increases (to a maximum of 99.99%). Luckily, this can be easily calibrated so that when you use a larger intake tube the ECU can accurately calculate fuel duty cycle.
These are just some of the basics, there is much more complex mapping inside the stock ECU, like transmission output torque tables, shift control tables, throttle control tables, throttle translation tables (from gas pedal angle). Volumetric filling, target filling, Various compensations for temperatures that alter fuel and ignition timing, and much much more. We will have more in depth information as we continue our development.
We are eager to see what we are capable of getting out of the Tundra N/A and Supercharged with a 91 and 93 octane stock ECU Reflash. Judging from the stock tables, we have a lot of room to play with.