The seat doesn't say to use 91 octane, it's the RON or Research Octane Number. Using 91 won't hurt your engine, but you'll just use more fuel, and receive the same power output. Look at page 29 in your owners manual. It can actually reduce your power, but it's to small to even be noticed. Depending on your elevation, you should use 87. However, if you're at a higher elevation, and you experience knocking or unusual noises from your engine, switch to a different octane or brand.
