I use a 2.5 gallon container (filled with 2.8 gallons of e85) and then top off with 5.8-6 gallons of 91. Where I live and fuel up, the local chevron has 5% ethanol.
I use this calculator:
http://www.georgebelton.com/E85Calculator.php
Typically, the e85 pumps where I get my fuel from read 82%-85%. Those factored in, i get a ballpark e29 to e31. Ive blended e85 and 91 using the same ratio and per the fuelit tester, I’m at e30.
Also, 2.8 gallons + 5.9 gallons is 8.7 gallons or +70% e30 fuel into your tank. At 25%, this tops you up to 95%.
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If I’m feeling lazy, I just go to the e85 pump...fuel up...disengage my e-brake and push my car to the 91 pump.
Having 2.5 gallons that allow for up to 2.8 gallons of fuel comes in handy for longer trips though. For road trips, expect around 250 miles before you have a quarter tank left... two of those 2.5 gallon cans Fit perfectly in the footwell area of the back seats so they don’t roll around.
I got my cans from Walmart.
https://www.walmart.com/ip/No-Spill-2-5-Gallon-Easy-Can/660681379
One full year. Between my RS and ST the past year (14k miles on the RS, 13k on the fiesta), all 4 of my cans have held up. No leaks in The Cali valley weather of yearly lows in the low-mid 30’s and highs up to 115 degrees.