[xxxBlakexxx]

Higher octane fuels burn slower than lower octane fuels. If you put 93 Octane in a stock GT, there is no performance gain, in fact, you can loose power if too high of an octane is used for the motor. If you put 87 Octane in a car designed to run on 91/93, the fuel will/can actually ignite early. This is called "knock", "ping", or "pre-mature ignition". When this ocurrs, the car looses power and damage can/will be done to the engine. In a bad case, it can sound like marbles rattling under your hood.

Think of "octane" as meaning "resistance to knock".

Most modern cars are equipped with knock sensors. My Ford servive manager told me that this is the case with my Mustang ('00) as well. These devices use a special pressure device that can sense knock before it ocurrs and adjusts the timing (advance, I think).

Most cars can experience conditions that would cause some knock or ping from time to time. These conditions can ocurr because of other factors such as load on the motor and outside temperatures or fuel that is not quite what it is rated. So as you can see, modern cars are constantly "thinking" and making adjustments.

In theory, a chip will allow you to advance your spark to take advantage of higher octane fuels. But if you use a chip you MUST always use high octane fuel. In my case, with my Diablo chip, it has a switch so I can turn it off and stay with 87 for those moments when gas hits $2.50 a gallon.

I agree, though, if you are going to add gears, wait for the chip. It will save you some bucks and a lot of time pulling the chip out again. Chips will also give you a little more top-end in your power as they generally raise your rev limiter a little and I believe most of the spark advance happens at higher rpms too. I suppose this would not do much for the low-end power issue that you complained about in a previous post and may even make it feel more pronounced.

I can say that my car pulls much better from about 4,000 rpms + that it did when stock. Although I have other mods that impact this.

Despite all the hoopla about mods, my favorite two mods so far on my Steedia Shifter and my rims. Both do crap for performance. Kind of funny huh? When I add my exhaust, I am sure that I will love that more than my "power adding" mods too. The more I learn, the more I wish I just stuck with wheels, exhaust, shifter, and gears. Throw in some nitrous and you have a quick machine.