# I taught someone how to save on 89 octane

#### Joe1

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 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?

I haven't seen a car that NEED 89 so far, either 87 or 91. Which car is it?

I haven't seen a car that NEED 89 so far, either 87 or 91. Which car is it?
He said the car specs 87, the friend just likes to spend extra money for worse performance.

Hoping OP was in Seattle; nothing better than a good WA WAWA story on a Wednesday.

Charlie Brown's teacher tells them occasionally.

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!!

He said the car specs 87, the friend just likes to spend extra money for worse performance.
Then why not just get 87 to save even more?

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.

Your acquaintance has a pretty serious lack of math skills, but good on you for helping out OP.

Next I'd teach your acquaintance how to calculate gas mileage so they can see how 87 returns the same mileage as 89.

Scott

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'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

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.

I was always told that 89 is mixed at pump in CA. 50/50 ratio of 87 and 91.
Doesn't it costs more to refine higher octane gas per octane point then it does for lower octane. I thought that's why Sunoco has separate tanks for each octane?

Here's a better idea. Pump only 87 octane but mix in TCW-3 oil at 640 to 1 ratio.

Does that increase the octane rating of the fuel?
Oil in gas generally REDUCES the octane.

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

Then why not just get 87 to save even more?
He might when it hits \$8/gal.

I was always told that 89 is mixed at pump in CA. 50/50 ratio of 87 and 91.

Same here... 89 is not actually blended at the refinery.

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