Gas is gas is gas is gas.
Only real difference is the additive package at some stations. (Shell it appears, like's to add too much cleaner to the fuel...)
Chevron has a very good cleaner called "techron" that has actually been proven to work at keeping your fuel system clean.
Octane is only a rating of how fast a fuel burns, and how easy it is to get to burn.
Higher octane fuels actually burn SLOWER and are harder to start burning v/s low octane that is very fast burning and lights off easy.
There is a demo I've seen where low octane fuel is put into a tube about 8' long made of glass, or plexiglass. (I'm not sure.)
Anyway, they put some low octane fuel vapor in the tube which is open on both ends, and then light one side.
There is a loud POP and the fuel is burned, you feel the flash of heat and it's over. You really can't see the flame front go down the tube it's so fast.
Then the higher octane fuel is brought out, the tube is blown out with fresh air, then the vapor added, and it's lit on one end. You hear a WHOSH sound, and clearly can see the flame front burn across the tube. It's still pretty fast, but you can see the flame move.
The point here is the fuel has to burn in your engine, and how fast and easy to light it is affects how much you can compress it before it's going to light on it's own. Also as the pressure comes up in the chamber, it's going to cause other areas of the fuel to ignight due to the spike in pressure. The lower octane fuels can burn so quick that the flame front is started, the pressure rises, and then other areas across the piston crown ignight, and the muliple flame fronts collide, and you hear a "PING" noise. (This is like your piston just got smacked by a 8lb drilling hammer.. only it's just from the pressure of the event, and it's very hard on your motor.)
Detonation or ping causes the boundry layer of gas that keeps your piston from melting to be disturbed, and that exposes the alluminum of the piston to very hot burning fuel. Aluminum melts at about 1103f, and fuel burns in the 2000 to 2500f range or more. So, why do your pistons not just melt in this environment? The gas boundry layer protects the metal from actually touching the burning fuel/air. Imagine a gas force field, and your getting the right idea. The extreme pressure wave caused by detonation breaks up the "force field" and in an instant super heats your piston and spark plug ground strap.
The "control" factor is the piston bore wall. As the flame front reaches it, the cooler wall quenches the flame and slows down the process. The lower octane fuels can burn so quickly that they are done before they reach the bore wall, and have disturbed and overheated many of the metal parts in the combustion chamber.
The now softer alloy piston can be damaged by the pressures, or you can have the engine killer event, pre-ignition.
This happens when the now glowing white hot metal parts are exposed to the incoming air and fuel mixture. The intake valve is open, the air/fuel mxi comes in, and it's ignighted by the hot metal parts.
The intake valve closes and the piston starts the trip back up to normally compress the mix and let the spark plug ignite it at the proper time... Only in this case, the burning has already started... Trying to compress the burning and expanding fuel mix is almost impossible, and the superheated parts are not as strong as they would be cold, so they bend, break or make new holes where they never were designed to be. (Like through the top of the piston crown.. or they turn your nice straight rod into a pretzel.) Minor damage generally results in broken ring lands and melted pistons. Major stuff is thrown rods and the resulting damage they create. (Time for a new engine.)
Ok, so on your NA would running lower octane fuel be a problem? Likely not unless your modified to the point where your running higher compression ratios.
I would run some toulene to clean your fuel system about every 4 months, but running Chevron gas will keep it clean as well. (Or you could spend money and buy Techron to add to your gas about every 4 months.)
If it was me, and you were not getting any ping noises, run the cheaper gas, you might even pick up some power actually since it burns so fast, and it will improve your emmissions too.
