Boost control

A 3-port MAC-style solenoid, PWM’d from a low-side (Low-side 9 is the convention in this manual), is the usual setup. The ECU does not “make boost.” It bleeds or redirects wastegate pressure so the gate stays shut longer.

Plumbing (3-port)

• Port 1 (normally closed to vent, check your valve): to wastegate actuator.
• Port 2 (common): to the intake / compressor reference.
• Port 3: vent to atmosphere (or to the intake pre-turbo, quietly).
• A mechanical gate spring sets the floor. Closed-loop boost cannot go below the spring in a typical 3-port bleed. If you need 0.6 bar and the spring is 1.0, change the spring.

Tune

1. 01Open loop

   Duty vs RPM (and gear if you want). Find the duty that makes the boost you want in each area. This is the feed-forward table closed loop will sit on.

2. 02Closed loop

   Target vs RPM / throttle / speed. Small authority until the open-loop table is close. A 40 % authority on a bad open-loop map oscillates the gate and the driveline.

3. 03Safety

   Overboost cut (fuel and/or spark) at a hard cap above target. This is not optional on a drift car that can stick a dump valve shut.