Tech Bulletin -Subaru - Wastegate Frequency & Behavior

Date: 1/17/18
By: Mike McGinnis

Vehicles affected:

• Subaru

Software affected:

• 1.9.1.0-15639 and newer

Firmware affected:

• not applicable

COBB has exposed the factory wastegate frequency table on a number of Subaru models. While wastegate frequency change does have a predictable result on wastegate solenoid on time (ECU output voltage low), wastegate behavior is not consistent across Subaru models due to differences in drive currentthe electrical systems. This bulletin is meant to provide some additional info to save you time and reduce surprises.

• 08-14 WRX and STI models have performed predictably at 10-30 Hz while using COBB boost control solenoids. Changing solenoid frequency within that range has not drastically affected wastegate flow. 
  • You may want to try increasing frequency to 15-30 Hz to reduce wastegate flutter.
• DIT and 02-05 WRX ECUs exhibit similar electrical behavior which results in long solenoid closing latency times. This results in boost increase without WGDC increase when you increase solenoid frequency, since the closing latency time becomes a more significant portion of the total period.
  • You may want to try increasing frequency to 15 Hz (not higher) to reduce wastegate flutter, but will have to reduce WGDC and turbo dynamics values to avoid boost increase. As with any boost tuning, we suggest starting with low WGDC values and working your way up gradually for safety.

We hope this Tech Bulletin helps you to more effectively tune wastegate frequency and duty cycle tables. If you have any feedback, questions, or concerns please let our Subaru Expert Group know