you can use mid grade its ok. but if you keep using reg the motor pings and can cause damage.but it all depends on the person.my dads 94 sh uses only primeum and it has about 140,000 i have been in newer preludes with the same motor and close to the same miles and the dont pull near as hard.its really worth it if you wanna keep the car for a wile.and i would also still sugest if you do uses a lower grade gas use primeum ever other couple tanks at least.