Lower octane fuel burn rate is faster. Lower octane will produce morepower in an enginePRIOR to deto or timing automatically pulled away. If you have a high compresion or highly tuned engine that produces high BMEP figures, then it will make more power on a higher octane fuel. Most ,if not all, new vehicles have a deto sensor on the engine and will pull timing away without hurting a thing. Mileage and power will sufferIF THAT HAPPENS. Cappachinoo and Jeffla haveit right! Some of youother guys are making uninformed statements or don't have a clue what you are saying, you end up mudding upthe waters. You only confuse the problem for people trying to figure something out. Don't post if you don't know! Bottom line is, 87 octane fuel will nothurt anything in your stock engine! Fuel mileage mayincrease by using it, as long as the deto sensor dosn't pull timing away. 2.7t for instance has low compresion and as long as you don't keep it under boost for long it will get better mileage with 87 octane. If you drive with your foot in the throttle chances are it will need more octane. There are a large number of variables that contribute to detonation. Problem is, you have no clue when it goes into deto cause the computer will pull timing away till it stops. You never hear a new car ping anymore! It is all controlled by the computer. You will lose power (mileage) if the computer pulls timing away, you will not however hurt a stock (read, unmodified) engine on 87 octane fuel. I ran 114,000 miles on a 2.7t using 87 octane fuel. Now my newsuper high compression 4.2 needs the 92 octane to get the best mileage and power. The computer pulls too much timing away on this one and reduces power and mileage. 87 octane still, will not hurt this engine.

 

Just because you can't hear pinging or knocking doesn't mean it isn't happening. Have you checked fuel economy with a few tanks of 93 vs. a few tanks of 87? I think you would soon find it doesn't cost you more to run premium fuel when you factor in the mileage.

Saving 10 or 15 cents a gallon isn't worth the potential damage to your vehicle. Consider that $1.50 per tank cheap insurance.

 

I pulled my information from this article http://en.wikipedia.org/wiki/Octane_rating, if you read this, it will answer most of your questions.