These data came from over a year's worth of stiff blend trials in the unmodified Nissan. This was a 1998 "Sentra". I had no way to draw fuel samples until the last two tanks of fuel, so the blend strength data are best-estimate E-numbers for what was added at each fill-up. All but one or two of these were fill-ups on top of quarter tank-or-less residuals, so it's a decent estimate, no matter what.
Although scattered at about plus-or-minus 10%, there does seem to be a very slight (5%) decline in fuel mileage between all gasoline and 25-something-% blends. Maybe. The decline is 5% when the scatter is plus-or-minus 10%. Maybe that drop is not actually real.
Theoretical lower heating value for an E-25 is 91% that of plain E-0 gasoline: a 9% drop. It would seem the car is doing better than heating values would indicate, although the scatter is too great to actually draw that conclusion. This is pretty much the same result as was seen with blend trials in the unmodified Ford F-150.
One tank (only) was accidentally too rich in ethanol at an estimated E-49. This one data point is about 80% of the E-0 mileage. Such a drop is big enough to be "real", even with plus-or-minus 10% scatter. There are points without drop at about E-40 to E-42. This behavior is consistent with stiff blend trials in the unmodified Ford, and with the ethanol VW as rigged to gasoline settings. (See the November 12, 2010 post just prior to this one). The VW data are spot-check "snapshots" from intake vacuum measurements, not tank averages of mileage.
That's three wildly-different cars providing the same quantitative answer, and from two different completely-different types of data. Stiff blends in unmodified vehicles provide essentially gasoline-only performance up to blend strengths in the E-40-to-42 range.
For the Nissan, I was able to cross-check the best-estimated E-numbers against actual test measurements on the last two tanks. Both were within two percent of being correct.
I see nothing here that contradicts the conclusions in the earlier post:
(1) Above E-42, timing seems to be late (low vacuum, low performance).
(2) Below E-42, you cannot practically tell these blends from a straight gasoline.
Considering that no sophisticated test equipment was used at all, these results are quite remarkable, are they not?