You should certainly try to run 91 or better. If you run 87 in case of emergency it wouldn’t be the end of the world as the computer would compensate for that by pulling timing. However you SHOULD RUN 91 (minimum) at all times if you can do so. Most newer cars have (2) different fuel maps and can change the timing as need be if they sense lower grade fuel. But since you have a high performance vehicle you shouldn’t use anything but premium fuel.
You could add an Octane booster of sorts to increase the octane rating. You do not have to drain the gas tank. You can also just be light on the gas pedal and burn up what you have. Again this is not a Major issue for you. Just take caution.
My husband (who never drives my STS-V) went to the gas station to fill it up for me today and the station was out of premium and was close to being out of regular unleaded due to a gas shortage/panic in our area. He fills it up with regular unleaded and sees no problem with that. I on the other hand had a come apart about it!
My questions are:
Would kicking him in the balls be a little too much ?
From the owner's manual.
"if your vehicle has the 4.4L V8 engine (VIN Code D),
use premium unleaded gasoline with a posted
octane rating of 91 or higher. For best performance, use
premium unleaded gasoline with a posted octane
rating of 93. In an emergency, you can use regular
unleaded gasoline with an octane rating of 87 or higher.
If 87 octane fuel is used, do not perform any aggressive
driving maneuvers such as wide open throttle
applications. You may also hear audible spark knock
during acceleration. Refill your tank with premium fuel as
soon as possible to avoid damaging your engine. If
you are using gasoline rated at 91 octane or higher and
you hear heavy knocking, your engine needs service."
Octane boosters really aren't worth what you spend on them. You see the high numbers the bottle say but read the fine print. If you need to use an additive run to the paint store or Lowes and pick up a can of toluene or xylene. When I used to race my Grand Prix GTP I would mix my own race gas with Toluene. Toluene carries an octane rating of 114 and xylen is 117, you would need many many bottles of the off the shelf stuff to equal a gallon of this good stuff!! Do not run this all the time , but if you like to race it may be wise to look into it. I used to mix one gallon of toluene with 4 gallons of gas and some marvel mystery oil for drag days.
If this original poster is getting 21.9 mpg as she stated originally, then she probably does not have a V model and is confused about what car she has. The label on the inside of the fuel cap cover says "premium fuel only." If it doesn't, she's on the wrong forum.
If it does, then who the heck thinks "only" means "optional"? Tell you hubby that he's risking voiding the warranty and the motor in this car is HAND MADE at the factory and will cost him over 10 grand to replace after he puts holes in the pistons in his short-sighted attempt to save ten bucks. Maybe that will get his attention.