Read your owners manual. The 5.4L will not get any better performance or mileage with higher octane fuel. It is designed to run on regular as are the vast majority of today's modern engines. Absolutely no reason (with 5.4l and most others), to spend more on a higher octane rating when towing or any other time. As noted that is something to look for when shopping for that next TV as it has a significant bearing on the actual cost of operation. I wish there were more places that sold non ethanol gas as it kills your mileage now matter what grade you are running.
As a chemical engineer I feel I have to way in on the topic. First off gasoline is a distilled blend of hydrocarbons that come from crude oil. Furthermore, gasoline is a mixture of various length hydrocarbon chains (not just one molecule type). The term octane itself refers to an 8 carbon chain molecule. The longer the carbon chain the more stable (less volatile/explosive) it is. For example propane (which we all should be familiar with) is a 3 carbon chain and anyone that has camped for long knows how easily it can burn and in the right conditions explode. So, the second peice of science that applies is the ideal gas law (PV=nRT). This basically states that the pressure (P) of a gas (fuel air mixture) in a specified volume (V) will be directly proportional to the temperature of the gas. If you think about this in the context of an engine cylinder as the piston rises during the compression stroke of a four cycle engine you are decreasing volume which in turn increases pressure (commonly known as compression in automotive circles). This in turn causes the temperature of the fuel air mixture to increase in temperature. If your engine runs high levels of compression it can cause the fuel air mixture to heat up to the ignition point prior to the spark plug firing. This premature detination is what is commonly known as spark knock.
So, the higher octane fuel is more stable and if your engine has a compression ratio that requires a higher octane fuel (as stated in the owners manual and/or on the gas fill door) you definitely should run it both for efficiency and prevention of damage to your engine. For those of us with engines with more normal compression ratios it really would not help you.
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The term octane itself refers to an 8 carbon chain molecule. The longer the carbon chain the more stable (less volatile/explosive) it is. For example propane (which we all should be familiar with) is a 3 carbon chain and anyone that has camped for long knows how easily it can burn and in the right conditions explode.
It almost sounds like you're trying to say propane has a lower octane rating than pump gas? Is that what you're trying to say?
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In the POL classes when I was in the Navy, we were taught that Octane Rating is a measure of the anti-knock capability of the fuel. That is, the ability to resist Pre-Ignition or detonation.
The "Motor" method of determining octane rating is to run a test engine on the fuel to be measured, then run it on a mixture of Normal Heptane (which is zero octane) and Iso-Octane (which is 100 octane). the mixture that gives the same anti-knock qualities as the test fuel will show the octane RATING of the test fuel. Thus, if 90% Iso-Octane with 10% Normal heptane is the mix that matches the test fuel, it is 90 octane fuel.
Of course, this also means that there can never be a fuel with over 100 octane rating. Anything above that (such as 115/145 Avgas) is a Performance Number, not an actual octane rating. (NOTE: That Aviation gasoline is no longer available, it had WAY too much Tetra-Ethyl Lead in it!)
The other method of determining octane rating is the Research Method, which I am not very familiar with, but sounds like pretty much of a SWAG (Scientific Wild A** Guess).
The octane rating noted on the pump is usually M+R/2, or an average of the two methods.
To cut to the bottom line, read the Owners Manual, and use the fuel that is called for therein. If you use a lower octane fuel, the computer will detune your engine to compensate for it. If you use a higher octane fuel, there will probably not be a noticeable benefit.
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In my state (Minnesota) ethanol is added to regular gasoline, but not to premium. Gas mileage is better using premium, but I believe this is mainly because it does not contain ethanol. The increase in mileage though is not worth the added cost in my RV. It is also against the law here to use premium in any vehicle that does not require it. They actually post that rule right on the pump.
beergardens writes "As soon as it removes that timing, mileage and performance both suffer."
Not necessarily will "performance and mileage suffer".
Modern engines tend to be able to compensate fast and often enough to squeeze every ounce of "mileage and performance" out of even the lowest grade of fuel.
In my case my own tests showed me that I was able to only get .1 mpg better using 93 octane. That to me indicates that 87 will work plenty fine and I will not gain enough mileage to warrant the extra cost of 93.
As far as performance, couldn't tell ANY difference. The only way I would be able to tell would be to have it dynoed, to me not worth the effort to find out.
"Therefore, the further your fuel can resist preigniting, the more timing advance your engine can run, and the better your performance and mileage will be."
Not necessarily. There is a breaking point of no returns with timing, once it gets to just under pinging that is the sweet spot which will return the best mileage and performance.
Since you have a fixed compression ratio you can not squeeze out any more mileage or performance with higher octane fuel.
There is no extra energy in high octane fuels (that is why folks choose diesel engines since diesel has much more BTUs than gas which allows diesel to get better mileage and higher torque at much lower RPMs), the octane level is more for the predetonation, doesn't mean you get more BTU (which is where the power comes from).
What the higher octane does for you is to allow the computer to add a slight bit more spark advance. This allows your engine to squeeze a very small amount more efficiency from the fuel. In some engines it may mean that you will get a good deal better performance and mileage and some nothing extra. It all depends on how well the manufacturer has the computer dialed in to the engine. Some do better job upfront (in my case) and some do not.
"Naturally, some engines are way more sensitive to this than others. Some are right on the verge of pinging under extreme conditions, some aren't. "
For that reason I stated that one needs to test their own vehicle and choose what works the best for their vehicle.
There is no "one size fits all" blanket statement for which is the best to use.
If your engine is designed to burn regular 87 octane, then you just waste your money to burn higher octane. Before computers and electronics that adjust to various conditions, then perhaps it made some sense but that's the old days.