From an economic viewpoint the best solution might be 88,89,90,etc. just blend 87/89/93 at the pump then worry about the relative humidity issues helping/hurting mpg. I'm getting close to needing tires and am contemplating the Continental True Contact for 80k milage rating and rubber compound. Debating going to 235 instead of 225.I know for a fact these engines get more hp with better gas. With 87 your lucky to get 215-220 hp with 93 your at 250. IMO that's not wasted.
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