Thread: Figuring octane when mixing fuel.

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Dont think you can mix the 2 to get 94 octane. I could be wrong though.

Assuming the two grades use the same octane boosters, a 3:1 mix should do it. I can't see that small a change making much diff, though. Try a tank of straight 100. Check timing and air-fuel ratio carefully. Hemi's are probably the least prone to pinging of any engine out there (no squish area) and those thick heads muffle any that does occur, so yours must have other issues besides the gas. Fix the pinging before increasing the boost. 15 pounds doubles the static CR, you'll never find good enough fuel for that with the present setup. What is your static CR, BTW?

My understanding is that the relationship is linear. If you mix 87 and 93 50/50you get 90. In your case you have nine points difference, 100-91, and you're looking for three points improvement so a linear relationship says put in ten gallons of 91 and five gallons of 100 and you should have 94. Now the kicker is that you need to do that every time - if you're out cruising, get to 1/4 tank and add 91 you will "dilute" your base of mixed 94 in the same relationship.
Disclaimer: There may be someone on here who is more of a fuels chemist than I, but I believe that stations that offer three octane levels simply blend their high test and low test 50/50 in the pumping process to hit the middle number. To my knowledge they do not have three storage tanks.
(RPope and I were typing at the same time. Glad the math was the same!!)

I agree with rspears. I used to do this in my '68 vet which had 12:1 cr. Mixing is a real pain though. You could instead try water vapor injection.

Kitz