Having gone down the rabbit hole of researching aftermarket ECUs for my cars I've discovered that in the US it's basically illegal to make changes to any part of a street legal car's emission control system which of course includes the ECU. It seems that it has been for several years but the EPA did not enforce the regulation consistently.

* https://www.saveourracecars.com/about.html

* https://www.aemelectronics.com/product-legal-restrictions

* https://tiremeetsroad.com/2021/07/13/how-californias-bar-app...