Quote:
Originally Posted by Skip Fix
To say because Pontiac used a wide lobe sep in their 10:1 motors they were designed for 87 or even 93 octane is way off, what was even regular leaded back in the 70s? I think Sunoco 260 was like 102 at the pump. A little different in a 10;1 than tghe ethanol 87 stuff you might get now.
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What many people don't realize about the early 70's and older octane ratings is that they are not the same ratings that are used today. So, that Sunoco 102 octane, would not be rated 102 octane today. It would calculate out to be about 96, still higher than what we have now, but not as big a difference as many people think. Here is why:
There are 2 ways that octane is measured. One method is called the "research" method, which is a high number. The other method is the "motor" method, which is much lower number. Back in the old days, the advertised and posted octane ratings were the higher "research" number. So, most premium gasoline was 100 "research" octane, Hess had 101, and Sunoco 260 had 102.
Sometime in the early 70's, the government changed the way the octane rating was to be posted on the pumps. The new octane numbers were changed to the average of the research and motor octane ratings. The formula is R+M/2. Averaging the research and motor octane ratings results in a lower number. So that same Premium gas that was posted as 100 "research" octane in 1971 was now posted on the pump as being 95 octane using the R+M/2 method.
And that is how octane ratings on pumps have been posted ever since. Next time you get gas, look at the octane rating sticker on the pump, and it will say R+M/2 on the sticker next to the number.
The 93 octane you buy today would be advertised as 98 octane, if it were posted by the "research" octane number like they used to do in the old days.
The point is that the gasoline we have now is a little lower in octane, but not drastically lower in octane compared to the old days. There's only about 2 octane real difference between 1970's advertised 100 octane Premium(research method) and today's 93 posted octane Premium(r+m/2 method).