Gas mileage for the Altima 3.5 SR was 34.5mph for a 200+ mile round trip on E15. I don't have an air fuel ratio gauge on the Altima on it so who knows. I will try the Mustang later this week It already has 8 gals of BP93 in it. I will add 4 gals of E85. That will give me E35 and 98.3 octane. See what the airfuel gauge says.