I taught someone how to save on 89 octane

Joined
Mar 14, 2003
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867
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USA
I have an acquaintance who drives a car that specs 87 octane, but for whatever reason this person insists on using 89 octane.

So this person was complaining how his beloved 89 octane now costs $4.739 at the Wawa vs $4.299 for regular. He further lamented the spread in price between 89 and 93 octane was $.16 ($4.899 per gallon), but $.44 between 87 and 89.

I said "put two thirds 87 in your tank and one third 93 and you have 89 octane for a cheaper price." He looked puzzled, but we did the math for 3 gallons. (4.299+4.299+4.899) is $13.49 4.739*3 is $14.21. Under this scenario, he is saving $.72 on 3 gallons or $.24 on one gallon.

He was elated. I'm in NJ and everything is full serve here. He did 2 separate transactions. One for 8 gallons of 87 and a separate transaction for 4 gallons of 93. He said the gas attendant wasn't overly happy. He's now telling everyone the story how he beat the system.
 

CKN

Joined
Oct 14, 2014
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9,652
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Utah
I have an acquaintance who drives a car that specs 87 octane, but for whatever reason this person insists on using 89 octane.

So this person was complaining how his beloved 89 octane now costs $4.739 at the Wawa vs $4.299 for regular. He further lamented the spread in price between 89 and 93 octane was $.16 ($4.899 per gallon), but $.44 between 87 and 89.

I said "put two thirds 87 in your tank and one third 93 and you have 89 octane for a cheaper price." He looked puzzled, but we did the math for 3 gallons. (4.299+4.299+4.899) is $13.49 4.739*3 is $14.21. Under this scenario, he is saving $.72 on 3 gallons or $.24 on one gallon.

He was elated. I'm in NJ and everything is full serve here. He did 2 separate transactions. One for 8 gallons of 87 and a separate transaction for 4 gallons of 93. He said the gas attendant wasn't overly happy. He's now telling everyone the story how he beat the system.
I guess it doesn't take much to get some people "elated". What else does he do for excitement?
 
Joined
Aug 23, 2010
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pa
in my area of Pa 93 is at least .80 or more a gallon + my summer car a 225Q audi TT REQUIRES 93 stock plus its TUNED. colder weather can sometimes allow a lower octane, BUT if knock happens it can be big $$$$. retired so i drive little so it costs less!!! my COAL burning Harman saves at least a thousand bucks yearly!!
 
Joined
Nov 11, 2018
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Great Lakes
The savings are hardly worth the effort. At 10 gallons and my local prices 89 would cost $46.50. Splitting it between 87 and 93 would cost $45.23.

I haven't seen a car that NEED 89 so far, either 87 or 91. Which car is it?
5.7 HEMI’s “recommend” it, but it seems highly dependent on the particular vehicle on if it actually makes a difference… the 360HP variant in my 2011 Durango I couldn’t tell any difference in performance or fuel economy between 87 and 89. The 395hp variant in my Ram feels a bit lethargic with 87.
 
Joined
Apr 27, 2010
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Suburban Washington DC
I'm not sure the dilution is linear as in 1 gallon of 87 plus one gallon of 93 equals 2 gallons of 90. You need a chemical engineer to explain it and I don't remember the details now, but it's something like the lower octane will reduce the higher octane rate greater than the ratio of the mix. So my example may give 89 octane and yours, 88. Not that your guy would ever notice.
 
Joined
Apr 24, 2018
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Wisconsin
I'm not sure the dilution is linear as in 1 gallon of 87 plus one gallon of 93 equals 2 gallons of 90. You need a chemical engineer to explain it and I don't remember the details now, but it's something like the lower octane will reduce the higher octane rate greater than the ratio of the mix. So my example may give 89 octane and yours, 88. Not that your guy would ever notice.
Blending for octane is more dependent on the positive side effects of ethanol vapor pressure inflection points.

AKA You can actually get a better fuel in reality than what the octane would suggest based on the percentage of ethanol.

Generally octane mixing is simple math, the vapor pressure may change more than expected but unless it’s -40F outside that is likely a positive not a negative and likewise vapor pressure isn’t octane
 
Joined
Aug 30, 2004
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28,596
Location
CA
I'm not sure the dilution is linear as in 1 gallon of 87 plus one gallon of 93 equals 2 gallons of 90. You need a chemical engineer to explain it and I don't remember the details now, but it's something like the lower octane will reduce the higher octane rate greater than the ratio of the mix. So my example may give 89 octane and yours, 88. Not that your guy would ever notice.
I was always told that 89 is mixed at pump in CA. 50/50 ratio of 87 and 91.
 

ZeeOSix

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Just don't show him how to mix oil visvosity to create frankinbrews. :LOL:
 
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