What have you done to "need" , "race gas"?
Here's my $.02...
You don't need any more octane than is required to perform without detonation.
Different driving habits and climate can affect this. On the older cars adding an octane booster, or using higher octane fuel was the only way to prevent or cure detonation. Newer vehicles now have a sensor that detects the knock and adjusts the timing to correct the condition.
Best performance is achieved running as much advance as possible without detonation. The trick is to find where you get the best performance/mileage.
It is very possible that a higher octane fuel could see an increase in both mileage and performance. If you are pinging on 87 octane and the PCM is retarding the timing to compensate, then a higher octane could improve the condition.
Remember
higher octane does not mean more power. It is a resistance to burning. This is necessary when a performance engine creates an atmosphere conducive to preignition. Engines designed to develop more power and having a higher final compression ratio may require higher octane fuel to avoid preignition. Engines not built this way will see no benefits beyond their own requirements. Best performance is developed with a complete burn. Lower octane burns easier. Higher octane is harder to burn.
I have a car that does require high octane fuel. I like the 115 Cam2 Purple racing fuel when I can get it. This engine develops in excess of 15:1 compression.
Having an engine that runs well on two different octane fuels is difficult at best. Usually that means being able to change the final compression ratio. The easiest way to do something like that on the fly, is adjusting boost. In my case I swap pulleys and run the blower under driven. Obviously that is not done on the fly. Mine will run on pump premium with a double dose of octane booster. Doesn't run great though.
Another option would be NO2. That would probably be the best application. However it still requires the fuel change to be close to the injection point and being very sure the engine is ingesting the higher octane fuel when the shot hits. A lean out backfire and or preignition is no fun at all under boost conditions. Risky. Better to have it all set up and ready to go before boosting. I do not have a turbo'd rig with adjustable waste gate, so I am not going to speculate on the needs there.
For all of those reasons and a few more, a dual fuel system really doesn't make much sense. Get it running perfect on one fuel.
(Not saying it can not be done. Just not as easy as having two different tanks of fuel)
