Sorry, I didn't know what kind of title I could put for this.

I have a '97 Subaru Impreza WRX STi and, as a technical project, I would like to remove the potential (haven't checked yet) 180km/h software speed limiter. This means dumping the ECU (done), reversing and removing the speed check (will begin soon) and reuploading (will be a pain in the butt, it seems, but I'm not there yet). To be exact, the ECU should stop the fuel when speed goes above 182km/h and starts it back again when it falls below 178km/h. In fifth gear, at 3000rpm, I'm already at 140 km/h and the car redlines at 8000 so I'm sure it has the power to go over that limit.

While doing this, I thought that instead of reflashing a custom firmware, fooling the speed sensor would probably be easier. But, from my understanding of fuel maps that my car (every car?) uses, this could mess fuel injection up and probably cause more harm than good.

And this is my question: would fooling the speed values between the sensor and the ECU mess fuel injection, or are the RPM and MAP the only values it would rely on ?

Before anyone ask: this project is tested on a racetrack (with helmet and stuff) and while the car is old, it's a project car so potentially breaking it is part of the game. This is all for the sake of "can I do it". I'm a computer security engineer and I love cars so I try to mix both of them to learn stuff. I don't plan on going 240 with the car (even if it has V speed rating tires), neither on public road nor racetrack (or maybe just once). I'm doing this project for the computer science part, but I'm always curious about learning how cars work.

Thanks! :)

  • 1
    Is this a manual transmission? Which speed sensor(s) are you considering modifying - do you mean wheel speed sensors? Do you know how engine RPM is determined on this vehicle - does it use the crankshaft position sensor or does it use a speed sensor in the transmission?
    – Zaid
    Jun 6, 2018 at 7:04
  • Just because you think you have 4000rpm to get you from 140km/h to 180+ does not mean that the engine has sufficient power to do so : the aerodynamic losses are increasing exponentially and when that equals the power output that is your max speed...
    – Solar Mike
    Jun 6, 2018 at 11:59
  • It is a manual transmission yes. I don't know yet, I haven't checked that part to be honest. I see. I haven't tested yet, but indeed, my bad
    – P1kachu
    Jun 6, 2018 at 13:17


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