[84LX89GT]

Higher octane gas burns slower and with less BTU's of energy, therefore it needs more heat to burn efficiently. In order to do this you must increase the compression ratio of the engine and have timing based on the increased burn time (higher compression ratio engines or engines with "fast burn" chambers require less total timing advance). Higher octane fuels burn more completely than lower octane fuels but the engine has to be designed or modified to take advantage of the higher octane fuel (some people advance their timing and run higher octane and may see a little bit more power and possibly better gas mileage).

In a vehicle designed for 87 octane, when you put in 92 octane without changing anything, it burns slower and as a result doesn't burn as completely which leaves more raw fuel in the oil, on the valves and on the pistons. This leads to carbon deposits and further problems down the line. In some cases you can see fuel mileage drop or power go down a little.

I personally would use whatever gas the manufacturer recommends you use for the vehicle unless you raise compression, add nitrous or boost, advance timing or change to more efficient cylinder heads.