Originally posted by TJ:
Think of it this way...the only thing the octane number does is tell you how fast the gas will burn. That's pretty much it.
The higher the octane, the slower it burns...
The slower it burns, the sooner the spark has to fire to get it going in time to push the piston with the explosion. (Timing)
If an engine is designed to adjust the timing to account for this, then higher octane fuel may improve performance.
In the X - the regular grade gas is pretty much the hot ticket.
If you drive all over the country...what is considered to be "regular" will change, mostly based upon the altitude of the region.
Regular gas at sea level areas (NJ) is around 87 octane...Regular gas in Colorado is more like 85 octane.
Thinner air has fewer molecules in the same space...so, to compensate, the gas needs to burn a bit faster for the same timing settings to work.
In other words, if you are going up into the mountains, and the engine starts to feel weaker, putting in a higher octane gas will make it worse, not better.
Hey TJ, nice way to put that - I remember seeing those lower 85 octane grades back when I lived in Wyoming, but never put 2 and 2 together.
Octane is also key in engine compression in that the higher the octane level, the more you can fit in a tighter space before it spontaneously combusts. This is important in engines that are designed for higher octane fuel, as low octane fuel will spontaneously combust under compression before the engine has ignited it - causing a knock, or explosion in the cylinder while the cylinder is still compressing.. Modern engines sense this (using knock sensors) and advance or retard the timing of the spark ignition to 'sync' with the fuels combustion level.
A good read on the subject can be found
HERE.