Tech Bulletin - 2018 WRX STI - Subaru Logic and OTS Calibration Changes

Date: 10/18/17
By: Mike McGinnis

Vehicles affected:

2018 Subaru WRX STI

Software affected:

1.9.1.0-15423 and newer

Firmware affected:

not applicable

While 2018 model year WRX STI vehicles remain largely the same as 2017, there are a few changes Subaru has made that we would like to make you aware of:

Boost Limiter Strategy - Subaru has adopted the base/adder strategy used on DIT WRX. That said, the separate Mode On and throttle based boost limiting functions were not included.
1. I've altered the axis break points on the Boost Targets and Boost Limits (Fuel Cut)(Wastegate Solenoid DTC) Base table values so they match in OTS files. This allows the base table to be populated with values from the highest requested torque column in the boost targets table, and the adder table set as your desired margin of safety. This is just one strategy, but one that may save you time so I thought I'd pass it along.
2. Should you choose to vary the margin of boost error from target with engine speed, you can alter the base table values accordingly.
Load Compensation (Manifold Pressure) - Subaru has made significant changes to these values again on USDM vehicles (not ADM), in an attempt to bandaid the fuel system pressure instability which causes the 08+ STI stumble. This seems to make the cars run better than previously in stock form, but is not a solution, and upon install of larger injectors you should expect the issue to become more pronounced. COBB's new Stage3 fuel system will resolve this issue for customers making up to about 400 wheel HP on E85, more on gas.
Flash Time - Flash time has increased due to a delay as data passes through Subaru's new CAN bus hardware. The combination of longer flash time combined with OEM battery quality concerns, may warrant use of a battery charger during flashes, especially during installation of the AP since it can take several minutes.

Time is money. We hope this Tech Bulletin combined with OTS performance maps which include these MY18 STI calibration updates allow you to more efficiently start tuning these new vehicles.

While Subaru made a few more calibration tweaks for MY18, we have avoided mentioning those which likely will not impact your work. If you have any feedback, questions, or concerns please let our Subaru Expert Group know!