Posted: Fri Sep 30, 2005 3:20 pm
Without going into too much detail, I'd like to correct a few misconceptions regarding fuels. I draw on my 17 years in the petroleum industry - including four as a chemist in an oil refinery laboratory.
When you mix different octanes of fuels, you will end up with a fuel that is the average of them both. Period. Your 50/50 mixture of 91 and 110 octane gas gives you 100.5 octane gas.
Octane is NOT a measure of the energy contained in gas. It is ONLY a measure of the fuel's ability to resist pre-detonation. If you want to measure energy, you need to use BTU/pound calculations.
What you need to know about is a concept called VAPOR PRESSURE. This is the ability of a petroleum product to turn to vapor at a certain temperature under one atmosphere of pressure. The higher the number, the easier it vaporizes. Asphalt is near zero. Propane is at 60. Gasoline runs at between 6 and 11 on the scale. This is where the fuel mixing has its effect.
Race gas (and Avgas) typically have a vapor pressure in the six range. They don't vaporize (atomize) very easily. This is done to help prevent vaporlock since race fuels are traditionally run in high-heat applications. 'Pump' gas usually runs between a 9 (Summer) and an 11 (Winter) on the scale. When race and pump gas are mixed, the vapor pressure comes out in the middle. This mix atomizes easier and therefore combusts more efficiently, giving you more usable power!
Me? I use only super no-lead. I throw in some fuel stabilizer (I buy mine at Home Depot) to help slow the vaporization of the gas's light-ends and to keep my system clean. Simple as that!
When you mix different octanes of fuels, you will end up with a fuel that is the average of them both. Period. Your 50/50 mixture of 91 and 110 octane gas gives you 100.5 octane gas.
Octane is NOT a measure of the energy contained in gas. It is ONLY a measure of the fuel's ability to resist pre-detonation. If you want to measure energy, you need to use BTU/pound calculations.
What you need to know about is a concept called VAPOR PRESSURE. This is the ability of a petroleum product to turn to vapor at a certain temperature under one atmosphere of pressure. The higher the number, the easier it vaporizes. Asphalt is near zero. Propane is at 60. Gasoline runs at between 6 and 11 on the scale. This is where the fuel mixing has its effect.
Race gas (and Avgas) typically have a vapor pressure in the six range. They don't vaporize (atomize) very easily. This is done to help prevent vaporlock since race fuels are traditionally run in high-heat applications. 'Pump' gas usually runs between a 9 (Summer) and an 11 (Winter) on the scale. When race and pump gas are mixed, the vapor pressure comes out in the middle. This mix atomizes easier and therefore combusts more efficiently, giving you more usable power!
Me? I use only super no-lead. I throw in some fuel stabilizer (I buy mine at Home Depot) to help slow the vaporization of the gas's light-ends and to keep my system clean. Simple as that!