This is the way it works guys:
The original Northstars were determined to require premium. After a couple years, Cadillac distributed an internal memo (which of course I recieved) that indicated that the Northstar could in fact handle lower grades of fuel. In the memo, they stated that the only problem that would be encountered would be slightly lower MPG and 0-60 times. They even included the test results in the memo. Unfortunately, a couple weeks after the issuance of the memo, I sent a memo to Cadillac engineering stating that after a short time on mid-grade fuel (90 octane) our fleet cars had all experienced an engine knock that we had traced to a "carbon-knock" caused by heavy carbon deposits. A dose of top-engine-cleaner had cured the knock but I felt that the engines had undergone an unusual amount of wear due to the knocking prior to the top-engine-cleaner. Immediately, Cadillac issued another memo stating that the Northstar should use only "premium".
Unfortunately, due to factors such as "Octane Distribution" etc., the ACTUAL octane found in any car, at any given time may vary quite a bit. As you may know, the engine management system can compensate for "some degree" of octane variation by retarding ignition timing. Again unfortunately, by the time the computer "senses" the need to retard timing, there has already been some degree of engine knock occuring. Plus once the timing is decreased, the engine performance and MPG will suffer proportionately to the amount of "compensation" the management system initiates.
Due to the vast variation in "actual" octane at any pump, at anytime, and the variation in condition of anyone's engine and/or management system, I always recommend using AT LEAST the recommended octane in their car.
Perfect example would be me and my car. The recommendation is for regular but I ALWAYS run premium. It's just a cheap insurance policy to me.
Oh, and BTW, octane boosters are far from cost a effective way to "routinely" raise the octane in your fuel.
