The smaller pulley and belt kit will deliver 9-11psi at sea-level on your Jeep Wrangler 4.0 equipped with a RIPP Supercharger system. This pulley is designed for high elevation clients to correct the superchargers impeller speed to offset elevation boost loss. At sea level it spools the blower faster and with more authority. Best of all as long as you have your Diablo tool up to date, it can be driven safely from sea level to high elevation without tune issue or need to switch back. You can always ask [email protected] before you install and they can direct you in the right direction for tune updates.