THUNDERMAX EFI SYSTEM. PN#309-591. APPLICATIONS; M8 models 2021UP Touring® Models Air & Twin Cooled (w/o center cool motor). Excludes 2023-2024 CVO (VVT) and 2024up center cooled motors.EXHAUST NOTE; 18MM LAMBDA SONDE. Installing a ThunderMax EFI may be in violation with local or EU laws. The ThunderMax EFI may not comply to local or EU emissions regulations. Check this or install at your own risk. | 