gasoline prefrence

[curtis73]

Higher octane levels slow down the burning which in turn slows down the flame front. A proportional advance in timing is recommended so the flame front still hits the piston at the same time. Using higher octane than is recommended can hurt top end power because the fact that the compression is too low for the slow flame front qualities will make the flame front too slow. A complete re-curving of the timing would compensate for this because the piston speed increases, but the flame front doesn't. but why re-curve and spend too much for fuel when you don't need to? Higher octane is recommended at times when compression is high enough that it causes overly fast flame fronts and pre-ignition/knock. If you don't have the compression to require the octane you're running, it may actually reduce power. WHEN the spark happens won't compensate for HOW FAST the flame can physically travel. Your owner's manual is a good guide for stock engines. Depending on your setup, it actually matters very little. Some guys say that the octane you use should be ten times your compression (i.e. 8.7:1 can use 87 octane) with obvious adjustments for aluminum heads and EFI. This is a pretty vague guess and there are extreme variations. My Impala SS LT1 with iron heads used 87 octane and had a 10.5:1 static ratio. My Honda Shadow VLX 600 has 7.9:1 compression under aluminum heads, but needs 92 octane (and it still knocks like a woodpecker)

These days, fuel companies fill your head with big brand-names of cleaning gasolines. Usually, its the alcohol that they add. I used to help out with the tankers up around Oil City, PA. Shell, Sheetz, Hess, Amoco, Exxon, Texaco, Mobil, and countless others all fill their tanks (at least motor oils and gasolines anyway) from the same exact pipelines in Altoona. Base motor oils and Gasolines are usually only separated by their additive package. Motor oil is potentially very different. Gasoline's additive packages are usually a powdered dye dropped in the tank before the fuel truck dumps fuel into it. That "clear" supreme fuel that is so special? Just 93 octane without the corporate dye. Some actually add detergents, but they do no more than a bottle of 65-cent fuel injector cleaner that you find in the parts store. If you think about it, gasoline is very specific about what it can and can't contain. Anything else would change its specific weight and that perfect 14.7:1 air/fuel ratio would be lean or rich depending on what brand you used. The government wouldn't allow that.

If I get off at an exit and I'm looking for fuel, I always (without exception) go to the cheapest place regardless of brand, appearance of the station, or how dirty the pump looks. The federal government keeps such close tabs on the condition of every single tank, pump, hose, and filter, that getting "bad" fuel is a very rare occurence. Even if you do get dirty fuel, chances are that the worst it will do is clog up your filter.

Another little tidbit. Gasoline contains no actual Octane. Octane is very hydrophyllic, meaning it absorbs water very easily. Octane was used very early on, but rusty tanks and rapidly degrading fuel lead to the use of tetraethyl lead. Boy, those were the days. Lead was good stuff.

Just my opinion from my short experience with those companies in PA.

In my experience, the cheaper fuel is probaby no different than Exxon, and may have even come from the same source.

Curtis Mittong