If you took a quarter a tank of 91 and 3/4 a tank of 87, would that give you like 89 or is that not possible.

 

I Believe the new octane would have to be somewhere between the two. It couldn't be higher, & wouldn't be lower. so I'd say your about right..

 

50/50 would yield 89.

 

Don't know the truth of this but I read somewhere that 2 different octanes will not mix.
So if you have a quarter tank of the cheap stuff on the bottom then add top the tank with the good stuff, you won't you wont be burnin the higher octane untill you burn the **** first.

 

That's not at all true. In fact, most all gas station only store 2 octanes of fuel, The high and the low. They are mixed at the pump for the mid grade. Saves a lot of money for producing and trucking 3 different types of fuel.

 

The 2 will mix fine.... that would be like saying bottled water, and tap water wouldnt mix... they are chemically so close to being the same.... and you are pretty close if not spot on for it being middle of the road numbers