If you look in the owner's manual for the car it says that 86 fuel will due, but there may be a time where the car will ping with 86 and then you should switch to 91. It mentions nothing of the HP, but it makes you wonder if the car just barely gets away with 86. There are many cars out there with ECUs that radically retard when you put a lower gas in. The WRX is a great example. It changes the boost level when you use a lower octane boost. There are people seeing big gains uses 113 octane in it. It's also a big selling point to have a car that uses more affordable gas. Out here it's 1.93 for 87 gas right now. My mom was not looking forward to a car that would require 91 (like my GSR). She liked the 6 speed V6 because of the ability to use 87 gas.