Quote:
Originally Posted by Flashmonkey
Here's a question for everyone. If the jerk before you used 87 octane gas, then you come puttering in and opt for 91....how much 87 gas (already in the hose out of the pump) gets into your tank before the 91 starts flowing in?
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It's a common worry on car and bike forums, but there's not much validity to it. There is < 1/4 gallon of fuel, at most, in the portion of the pump that would remain from the prior customer. Even a small bike tank where someone fills up 3 gallons, the worst case would be 1/12 * 87 octane and 11/12 * 91 octane, which for all intents and purposes would result in 91 octane in your tank. Keep in mind that fuel companies often overshoot the octane number as it can drop over time and it is required to meet certain standards when tested later at the end of the line (at the gas station). Unless someone fills up 1/2 gallon at a time, it's just not a worry.
Quote:
Originally Posted by Flashmonkey
This doesn't even account for the amount of ethanol certain companies put into their gas additive package that effectively lowers the octane rating further.
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Ethanol is actually one of the most common ways to *raise* the octane level. The high ethanol content gas means that much less of other additives and treatments are necessary to meet the octane rating requirements. Ethanol has less available power in it by weight compared to standard gasoline, but its octane rating is quite high.