Yep it does get you better mpg! I've done it countless times.. (when I could afford it or wanted to 'clean out' a fuel system)
From what I've read years ago, the higher octane actually slows down the flame travel so it burns more efficiently across the crown as the piston passes TDC and it pushes more on the downstroke of the rod.
That's why on High comp engines, you will have pre-detonation or 'pinging' BEFORE TDC. If it was firing just after TDC, it wouldn't 'ping' at all because the resistance of the crank being at TDC would already be past and heading down the other side... Make sense to ya?
NOW, what may be happening in a number of peoples engines is that gas stations are selling crap gas for premium prices and thus crapps out the O2 sensor, gives false readings to the ECU, cloggs up the cat, overheats it and forces the exhaust back into the engine eventually killing it...
SO, Just do some cheap things first.. Check if your grounds are clean/tight, pull your cap, check for RED DEATH (red dust that is produced by dieing bushings, needs to be replaced) Scrape your connections inside cap/on rotor, (spray with good silicone) make sure timing is CORRECT (not 'by ear'. If timing is off you will be chasing your tail by adjusting other stuff that isn't the problem) Get some NGK V-groove plugs that are for your heat-range. Don't get all caught up with the multi-tipped plugs, You can't change physics of electricity! OHM-out your wires, should be around 1000/ft or less (less is more $$$)
If you have a 1-wire o2, configure a 4-wired one. (it's helped me even on OBD-0! Minimal, but none the less) If your emissions will allow, header without the cat, OPEN up that exhaust. (enngines are AIR PUMPS, free it up)
Do these or some, log your results per week, and make changes that your $$ alow, keep more logs and then help someone else out by making a thread.. Who knows, it might end up as a 'sticky'
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