Yes, do the math and put in the E85 first, then top it off. Don't be concerned if you see a small drop in mileage on the first tank. The computer needs time to adjust for the different O2 level from the ethanol. Be patient and see what you get with the second tank at the same blend. I will definately say my Z-tec likes this blend! I saw better mileage and performance from the first tank with the blend. My son has a ZX3 also with the Z-tec and he is doing this too with the same results.