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The GE is actually spec'd for higher octane than the GTE... So 87 for the GTE and 91 for the GE or around there... altitude, ambient air temp and humidity all play a part in determining what octane is best for your situation. I ran 87 in my GE but only because I'm a mile above sea level and the air is thinner. The difference in price between mid grade and high grade (when it's not free of course) is only a couple dollars per full tank... it's cheap insurance. BUT, also to keep in mind is that the higher the octane the less power it makes per unit.

Advancing the ignition timing (the spark advance, not the same as the mechanical timing) accomplishes very little. The ECU will push the timing as far forward as its ignition maps allow... this is allot further than the 6? you've advanced it... and once it detects knock it'll retard it until the knock is gone. There will be a bit of a difference when the car is cold and running in open loop (not the time when you want to push the engine too hard), but once up to temp it's back in the ECU's hands.

The ECU adjusts timing for knock and ping, but knock due to detonation isn't something that adjusting timing is going to help with... the fuel is exploding versus burning at a predictable rate and in a predictable pattern.

My recommendations to you are to use come Mopar combustion chamber cleaner to get the pistons and valves nice and clean and then to use a GOOD octane booster. I'm assuming you've got plenty of humid, but I know you've got plenty of heat too. Also, get the mechanical timing sorted out and get the ignition timing in check; It should be 10? BTDC.



EDIT: I should mention that fuel octane grades vary by region.... here we have 85 as the lowest, 87 mid and 91 high... this is M+R/2, there are a couple different standards for rating octane, the US uses the two methods averaged. I know in some places in the US 87 is the lowest and 93 or 94 is the highest with 89 in the middle; This is generally in the higher temp and drier climates.