*DBW* Drive By Wire Tuning FAQ

[bigBADbenny]

Please add your knowledge to this DBW FAQ.
I got stuck into the research at RomRaider.com but it all got very technical very quickly.
DBW is a great thing, or can be, and since nearly everyone (stock tuned) is stuck with it, why not understand and exploit this feature to its fullest?
Coyote's Guide to DIY Drive By Wire tuning
Nasioc: Subaru Drive By Wire and How to Improve it
Nasioc: Tuning DBW... A systematic appoach?
This is not intended to uncover the secrets of the great DBW tuners, more to promote the services and options they offer in their tunes.
This is a work in progress, so here are some possible headings for the research. I'll start with what I know already, then we can fill the knowledge gaps...

Glossary of common DBW terminology
Drive by wire:
an electronically controlled throttle, not cable actuated. Between your foot and the throttle plate are sensors wires and the ECU and a motor controlling the angle of the plate. Basically the ECU is able to modify the drivers input as regards throttle control.
Requested torque:

How DBW operates as stock standard:

Official version:
"i mode" gentle throttle angle/wastegate boost pressure (9?psi stock)
"s mode" medium throttle angle/max boost pressure (16?psi stock)
"s# mode" high throttle angle/max boost pressure (16?psi stock)

Whats actually going on with the ecu parameters:
"i mode"
"s mode"
"s# mode"

Vehicle specific DBW differences: 2.5T vs H6 vs 2.5 etc:

What parameters of DBW can be modified in the tune:
If your tuner is god-like, your SI-drive controller becomes the key to your Lib's Jeckyl and Hyde personality.

Common configurations via tuning.

For drivability, e.g.:
The standard DBW settings were on of the major reasons to get tuned for sure.
But S# in the first tune was EXTREME.
I asked my buddy Bruce what to ask the tuner for, in order to make S# more manageable.
"70% requested torque" was the answer...

SI-Drive as 3 stage boost controller:
"i mode" wastegate pressure, when you want to run the lowest boost possible as dictated by the wastegate spring.
"s mode" 14psi for moderately sporty driving
"s# mode" 18psi for going all out, similar to the overboost function on some sports cars.

[bigBADbenny]

reserved

[bigBADbenny]

reserved

[311logan311]

Figured I'd put in some input:

Your DBW parameters are comprised of two key functions:
"requested torque" - which in reality is an arbitrary value, but plays a key roll

and

"target throttle plate position" - not to be confused with your accelerator angle

Requested torque is a numerical value based on the accelerator angle and your RPM (engine speed). This value is different on different models of Subaru's. Example: I use 350 as my "maximum" numeric value. That means 350 = 100% accelerator angle in my case.

The car uses the Target Throttle Plate Position as its actual input, relating to throttle position to your ECU. Example, I tell my car that I want 12.5psi of boost at a value of 300 requested torque. Depending on how I've scaled my requested torque parameters and my target throttle plate position, this could happen when my target throttle plate position is at 50%, however my foot might be only actually pressing down 30% accelerator angle.

In tuning this is a great feature. I can make it so that when your foot is pressing down on the gas pedal at 50%, the ECU is telling the target throttle plate position it's "really" being pressed at 80%.

The advantage is quicker throttle response, boost and acceleration, when done properly. These parameters can all be scaled to complement each other, but if they are not done properly, your car can either act very sluggish, or very jerky on and off the throttle.

In relation to the S drive tables, Simply look at it this way:

Sport sharp will be at 350 requested torque = 100% throttle angle
Sport can be scaled in a similar way and then have a max requested torque value of say 340 = 100% throttle angle
Intelligent can be scaled lower across the requested torque parameter and max out at say 300 = 100% throttle angle

Going back to using 300 requested torque to have a value of 12.5psi in your boost table, your max boost at 100% pedal to the floor would be 12.5psi in Intelligent mode.

I hope that made sense and was helpful to someone. If you have any questions you want to ask me directly, just shoot me a pm!

[bigBADbenny]

Nice one!

[311logan311]

Thank you. I wrote that up pretty quickly, so there might be a few things to add/edit.