compression ratio + pump gas

kittypancake said

So the octane rating system has changed since the "old days"?

Click to expand...

Yes , and I don't know when the change took place .

That equation that's on the octane ratings' stickers :
" R+M/2 "
equates to
Research Octane Number + Motor Octane Number , divided by 2 .
This is also known by the American Petroleum Institute as the "AKI" number ( Anti Knock Index ).

Research Octane Number ( "RON" ) is a lower number .
Motor Octane Number ( "MON" ) is a higher number .
I *believe* that these numbers were used in regard to elevation / altitude , with RON used at high altitudes , and MON being applied to low(er) altitudes .
So , take a RON rating of , say , 95 octane ; then take a MON rating of 105 ; add both numbers , then divide them by 2 .
That results in a modern rating of 100 octane .

Again , I have no idea when the changeover took place . I can however say that it's been more than 20 years ago since the change occurred .