Last Friday, I was on my work phone walking another tech through some stuff so I was in work mode. I stopped for gas and accidentally put 9.3 gallons of 87 in my Tahoe before I realized what I had done. I drove it home gently. Took it Saturday morning to a RaceTrac about 22 miles away cuz that's my nearest E-85 station. I've been wanting to try a tank of E-85 since replacing the O2 sensors a couple years ago, anyway. I brought my laptop to scan for knock to see just how bad it was. Maybe the 45° IATs helped, but I could drive pretty normally and it was fine. But, as soon as I got a little frisky with the throttle- 4° of KR.
I got 16.75 gallons ($2.38/gal for those counting) of the corn oil and continued down the highway to get some miles on it to see what the virtual sensor would settle at. I've only tried E-85 once before, a couple of years ago. The highest it calculated back then was around 22% with an actual measured content of 65%. I've done the engine work and replaced the O2 sensors since then. Today, the highest I saw was in the 50s percentiles. After about 11 miles, it seemed to have settled at 40.8. The E-85 made a huge difference. I got a little more aggressive leaving each traffic light while watching for KR and there was none. I pulled in to Walmart and, while stopped at the far end of the lot, stomped it and saw 2°. I went in the store for a few things and grabbed a couple bottles of Lucas Octane Booster as well. Once home, I took a sample at the fuel rail to see what the actual net alcohol content is, then poured in the two bottles of booster.
The fuel in the test vial settled to 45%:
I'm feeling a lot better about mine accurately calculating the alcohol content. But, I still want a physical sensor.
I've been racking my pea-brain trying to figure out what that E45 blend yields in octane. The interwebz say that E85 is around 108 octane. I guess I need to know how many gallons I have of whatever is now in the tank to calculate it. I just thought I could equate "If 85% alcohol equals 108 octane, then 45% alcohol would equal 52.9 octane." I know this isn't right. I'm not mathing today.