The HO305 is perfectly happy on 87 octane IF the egr system is operating, the base timing is set correctly, and if there is a normal amount of backpressure in the exhaust. Additionally, the fresh air, preheated air valve must be in good order on the air filter. If you don't mind paying a little extra for premium or mid grade, advance the base timing 2-4 degrees. Base timing is set with the ecu/distributor wire disconnected. Standard timing is in the 4-6 degree BTDC range. After setting the timing re connect the ecu wire and the timing will jump off the damper scale. The check engine light will also now be lit so plan on unplugging the ecu for 30 seconds to erase the codes. I used up to 12 degrees base timing on my original LG4/ 305 and it was worth 12 HP! The engine will feel slightly more responsive and fuel mileage will improve. Have fun! Andy Jones