P1kachu has been hacking his 1997 Subaru Impreza STi.

The ’97 Impreza uses an engine control unit (ECU) and provides a diagnostic connector for external communication.  P1ckachu built a diagnostic interface device, got a dump of the ECU’s firmware, and reverse engineered the binary to figure out how to disable the speed limiter.  The custom interface uses a Teensy 3.2 and logic level converter to convert the Teensy’s 3.3v to the car’s 5v.

P1kachu has a great write up the project on this page.

Code for the project is published on GitHub.