Race gas mixture!

[juicyjosh]

It's not harmful to the engine, and the best ratio is 0:1.

If your engine is stock, the ecu has been mapped by Toyota to run on regular American gas. Simply putting 110 octane into a stock Yaris engine doesn't turn it into a racing engine. Instead, compared to regular gasoline, the stock Yaris engine with "110 octane" in the tank will produce less power due to the fewer number of high energy molecules per volume injected into the engine, per the chemical composition of the fuel designated as "110 octane." Less power per volume of fuel means that more "110 octane" fuel is required by the engine to produce the same power and torque produced by a comparatively lesser volume of 87 gas, so fuel mileage is also reduced.

High(er) octane fuel is used to help prevent preignition and detonation in forced induction systems or in high compression N/A applications. A stock Yaris engine is neither of these.