[mrtexas]

Octane is a rather mysterious and technical subject. Higher octane means more resistance to igniting by compression rather than spark. Igniting by compression gives knock, a sound that can be heard as a clattering noise. Higher octane doesn't burn cleaner or more efficient or "slower." Higher octane allows running higher compression which most of us don't do and stick to the very low 6:1 ratio of the v8 flathead. Shave your heads on a flathead v8 to raise the compression and you may need higher than 87 regular grade octane.

Research octane used to be the octane method before unleaded gasoline. Remember the old 100 octane(research) leaded gasoline? It would be equivalent to today's 93 octane(road) gasoline. When the USA started requiring unleaded some fuels started knocking in city driving at the same research octane. The EPA came up with the motor method which simulates city driving and required it also be satisfied.

Octane is measured on a standard one cylinder motor. An unknown sample is compared to a sample of known octane with an analog meter measuring knock. The knock engine laboratory I often visited in the refinery I worked at as an engineer had 8 or so engines going all the time and a cacaphony of knocking going on. The known octane samples are a mixture of n-heptane of 0 octane and iso-octane of 100 octane. Any octanes of greater than 100 are obtained by adding lead.

Regular gasoline is 87 octane a sea level. As elevation goes up octane requirements go down. So Regular is 85 octane in Denver at 5,000 feet.

Wish I had used no alcohol gas in my 49 Ford. I let it sit for a couple years without use and the in tank fuel pump and gas gauge rusted up solid from the moisture the alcohol had attracted. The tank is plastic so no rust there but cost me $200 to replace the rusted parts. It's a 25 mile trip one way for me to get no alcohol premium gasoline and costs $1 more than premium so $3.75 rather than $2.75 a gallon.