I've noticed a nearly 10% increase in fuel eccomomy in both a 2010 Prius and 2017 Prius V when using E0. The same experiment in a 2016 Accord netted only a 3% gain. I wonder if this has anything to do with the Atkinson cycle?
I’ll be testing this soon in our 07 Honda Fit.
On a trip last week to South GA (which is approx 300 ft above sea level) from Atlanta (1,050 ft above), we got 32 MPG using typical 87 E10 on the trip down elevation.
However, we also got a chance to refill using 90 non-ethanol E0 from a Marathon (top tier) for only $4.25 vs $3.99 87 E10. The return trip going up elevation was 36 MPG

and it “subjectively” felt a little smoother with slightly less hesitation while passing.
Probably placebo, so far, and anecdotal at best, but with this recent experience it got me wondering…and the best price I can find for 90 E0 in my area of metro-ATL is $4.59 at a Chevron nearby compared to my usual source which is Costco 87 E10 at $3.79.
I got some rewards with Chevron for .25 off per gallon for being a new member, so 13% more cost isn’t the worst *if* I can see whether a 10%+ MPG improvement is repeatable.
Unfortunately, the 90 E0 Marathon options are over $5 per in contrast, but I’d imagine Chevron 90 E0 is of equal quality. I had wished the metro pricing on Marathon fuel 90 E0 would’ve matched South GA.
