will cause the octane rating to plummet.
Isn't that kind of a good thing?
Plummet means to decrease, to cause the octane number to become smaller. A fuel with a low octane rating will combust on the compression stroke of the engine without needing to be ignited by the spark plug, it will cause the engine to ping or, in the extreme case, cause the engine to diesel. Thus a low octane rating is good, even necessary, for a diesel engine but bad for other types of engines.
Baseline Does Not Exist.