Octane has nothing to do with power. Gasoline manufacturers add more octane to prevent the premature ignition of the gasoline. In a high performance engine with higher compression, 87 octane will ignite itself from the heat of compression during the compression stroke or from any carbon buildup inside the combustion chamber. The computer will see that as a misfire and the incomplete combustion gasses will flow down to the catalytic converter. There, any unburned gasses will be burned off. 87 octane, 93 octane, misfire, wrong fuel. Unfortunately, all that extra unburned fuel raises the temperatures inside the converter—sometimes to the point of melting the precious metals inside.

The pre-ignition of the lower octane fuel will cause the engine to “ping” and that pinging will be detected by the computer’s knock sensor. The computer will retard the timing to try and compensate and more closely match the spark event to the actual combustion. But the computer will be chasing an unknown. You will lose power and fuel economy will suffer at the very least. You might also see a Check Engine light with misfire codes. It’s a bad idea all around. You gain nothing and you risk damaging the catalytic converter.

On the other note, it is OK to run 93 octane in an 87 octane engine, in fact I recommend it every third or fourth tank full. It helps clean deposits from the valves, pistons and heads, which keeps the engine running better and lasting longer. As a matter of fact, I always use 93 octane when I get on the highway for extended periods, thus effectively cleaning the above areas listed of carbon deposits. It does not hurt to run a can of a good quality fuel system, fuel injector or carburetor cleaner through you tank every few months also.

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