I want to drive the Evo X across every part of the US over time...

If I have my Evo X tuned, it's completely stock right now, what is the safest octane to tune for?

 

91, or if you have an accessport you can have multiple maps and switch as necessary

 

Like Dandbest said, 91 is the safe bet to go.

Other than that, if you are taking road trips with an Evo (or any sportscar), you might also want a radar detector and related accessories, as well as aftermarket sound deadening (for the Evo, at least trunk floor, better trunk floor, roof, under the back seats, and doors) to save your ears. Here is my trunk floor with Dynamat SuperLite:


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Attachment 326902

 

I drove my Evo from New Mexico to Ohio on a 91 tune no issues. Raised it an inch because I was slammed pretty good in New Mexico. Sound deadening would have been a plus, lol.

 

I actually think you would be just fine to tune on 93. I've run multiple 93 tune at higher elevation. The whole reason the octane drops at higher elevation is because the lower dynamic compression ratio reduces horsepower and the potential for knock. I would feel comfortable running a 93 octane tune anywhere that premium is available.

Edit: I reread that you said "safest". The safest would be 91 I suppose.

 

Right, it would be fine to tune on 93 and drive across the country.

Now if you were doing events and racing it where 93 is not available, then that's probably not advisable. But just driving normal with 91 octane, that is perfectly fine on a 93 tune.