Well, I reached the point in my phase I flight testing where I wanted to see how the engine would run on unleaded auto fuel. I have a Superior IO-360 with one mag and a single Lightspeed Plasma II+ EI. I had flown down to about 5 or 6 gal in each wing tank, so I filled the right tank up with 91 octane no ethanol auto fuel ($1.70/gal) and the left tank with 100LL ($4.00/gal). I did my takeoff and climb with the 100LL, and when I reached my cruise altitude (7.5K) I leaned the mixture to 30 degrees LOP. After letting things stabilize, I switched tanks to the auto gas and waited several minutes to see if I could see any change. The winds were very strong, and the ride was bumpy, but as near as I could tell there was no change in performance. I would have flown more tests including climb performance, etc., but given the winds and ride I didn't think I would get much valuable info. I returned to the pattern and landed uneventfully burning the auto gas, but when I taxied in I noticed that the engine didn't feel as smooth at idle as I was used to. I played with the mixture some, but no help. Back at the hanger, I tried one ignition at a time. What I found was that when I was idling with only the mag, the engine was idling very poorly. When I used the EI, it was better, but not as smooth as I'm used to. I then switched tanks back to the 100LL, and within a few minutes the engine was idling as smoothly as it aways does. I guess from here I'll wait to a better day to fly more testing, but I'd classify today as mixed results. I would sure have liked to have seen no difference between the two, but that wasn't the case, on the other hand at cruise power the auto fuel seemed great. If anyone else has any experience along these lines I'd love to hear about it. Perhaps I should just adjust my idle up to 900 from the 650 I have now and say "good enough." I really like saving $2.30 a gal.
Mark
Mark