I'm with Bubba and Rich. Put the good stuff in. (premium)

 

I say use premium, when I first recieved my car I used 87 because I didnt know any better... now switching to 91 and I do notice better fuel economy..

 

I have in the past put 89 in my formy during the winter (in FL, that means under 80°F ). That was during weeeks I expected no action. Since I do 60 mi. a day on I-95 I burn through tanks pretty quick. Never had an issue, aside from the car being a bit lazy.

Always run 93 when weather's warm or if you are foot-happy.

 

I use 93. Which if I'm not mistaken the manual says to only use premium fuel. There's also a small sticker on the backside of the fuel door that reads "Premium Unleaded Fuel Recommened". Pretty much says it.

 

Every manual I've looked at indicates exactly what "liltxboi911" quoted in his post in page 1 of this thread..... use 91 or higher, you can use lower octane, but performance may be reduced.

And as noted in another post, the specific octane requirement varies with altitude and with intake air temperature. You may not need the same octane in the cooler winter months, and you definitely don't need 93 octane if you live in Denver.

For max performance, follow the manual. If you have a scanner, check for knock retard when running low octane fuel. If you have knock retard, you are giving up HP.