One misunderstanding that some people have is they think today's premium is much less octane than it was in the 60's. They remember the 100 octane premium ratings, as compared to today's 93 octane premium and think that yesterday's gas was 7 points higher octane. But it's not really as far apart as it seems, because the ratings are posted differently now than they were in the 60's.
There are 2 methods of measuring octane. One is "research" octane and the other is "motor" octane. The research octane number is always higher than the motor octane number. Back in the 60's and up to the early 70's, the octane rating that was posted on the gas pumps was the "research" octane number, which is the higher number. The gas companies wanted to advertise the highest number to make their gas seem better. I worked for HESS a few years around that time and they even bumped their Premium up to 101 octane for a while, so they could advertise HESS 101 octane at the stations. So, most Premium was around 100, but that was the "Research" octane number only.
Early in the 70's, the government made the oil companies start posting their octane ratings as an average of Research octane and Motor octane. You will see that formula on octane rating stickers on pumps still to this day. Look closely and it will say R+M/2. Averaging the Research number with the lower Motor number produces a lower number of course, which is the number you see today. So today's 93 octane Premium is a result of the R+M/2 formula. If you were to go back to the 60's and take that 100 octane premium and figure it through the R+M/2 formula, it would be much closer to today's 93 figure. So, while there may still be a point or two difference, the difference in actual octane between then and now is not as much as some people think. Certainly not even close to 7 points difference.
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