Here is a couple of more of my own tidbits… I have always felt this way and did quite a bit of reading on the topic of fuels. Unfortunately I have not found any well designed tests with data proving anything.
The octane rating describes the fuels properties to resist detonation and pre-ignition. That is it. The other fuel properties [BTU’s, how volatile, flame speed, flash point, etc] are related to the entire blend of the fuel, not the octane rating solely. Higher octane fuels DO NOT necessarily contain less energy or burn slower. I assume it is easy to guess incorrectly because if one were to add dense aromatics to the fuel in order to raise the octane you “could” lower the energy per unit of the fuel. Fact is there are 87 octane fuels containing higher BTU’s per unit than 93 octane fuels and vice versa.
The Flash Point for gasoline is <-40 [F or C as they are the same at that temp]. If you go to this link which contains the MSDS sheets for certain fuels you will see that most fuels have the same flash point listed for their regular, mid-grade and premium fuels.
http://hazard.com/msds/gn.cgi?query=gasoline
Even if the flash point varied, a good spark plug being fired by a healthy ignition system is not going to have any problem igniting the a/f mixture regardless of it being 87 or 93 octane. Besides, gasoline is blended differently depending upon geographical location and season. The Reid Vapor Pressure of the fuel is the property that would have the consequences of hard starting or vapor lock if the temperature and RVP were not compatible. Seriously, think about it. If high octane fuel was blended in a way where it made cold weather starts difficult it would inconvenience all who own vehicles that require high octane fuel. I doubt that is the case.
Originally posted by SWLathrop
The higher the octane the higher the "FLASH" point meaning the harder it is for the fuel to ignite. The lower the octane, the more volitile it becomes. Most all vehicles are designed to run on 87 octane because they all have a low compression ratio which means you need a bigger faster flame front to occur in the cylinder. The higher the compression ration, or the more timing advance beyond factory setting, then the higher the octane one needs to go to eliminate the "PING" monster (pre-ignition).
Harder for the fuel to ignite in what circumstance? I would agree if were discussing a welding crew in the vicinity of fuel. As far as your “healthy” ignition system goes there should be no noticeably differences igniting 87 or 93. The engines in question have low compression ratio’s because the are low horsepower engines with long term reliability in mind. Advanced timing at lower rpm’s requires higher octane fuel because there is more time for detonation to occur as the a/f mixture is ignited earlier. I will agree that different fuel will have different ignition timing points that are optimal but it is dependant on many variables, not just the octane of the fuel.
And the winter time makes it even worse. I don't know how many times that I've helped people get their vehicles started because they were running "SUPER UNLEADED" when it wasn't required. The darn things just don't like to fire.
I disagree with this statement the most. Seasonal blends of fuel are made by the manufactures. If someone is experiencing cold weather starting issues it is related to something other that the fuel octane ran.
In closing I run 87 in my ‘X’ but only purchase gas from companies such as Chveron, Shell, Exxon-Mobil, etc…. I do not buy gas from ‘Mr. Gas’ or ‘Gas City.’
You should all read the book High Performance Fuels and Fluids. It is very informative. Unfortunately, nothing will convince me 100% until I see data from a well set up test.
