Local gas station now offering 90 octane w/o ethanol, which I topped off last quarter tank, car ran as well as ever. I've always used 93 and no particular brand. With the state of engine management being what it is today (2014 4.7 with 35K fyi) I am leaning toward the ethanol-free 90 going forward, not being particularly sensitive to some "at the limit" decrease in performance.

Thoughts/experience?

 

While I dont like storing cars with ethanol in the gas I dont worry about 10 percent ethanol. I do worry about preignition...

 

Eh, 90 octane is pretty low, and detecting knock often cuts timing quite a bit making the car run worse. What's wrong with 10% ethanol?

 

Hmmm...glad I asked as I had thought avoidance of ethanol would take priority. A bit into the weeds, but reading over the following article “Engine Basics: Detonation and Pre-Ignition” was both enlightening and caution-inducing.

http://www.contactmagazine.com/Issue...ineBasics.html

 

Water absorption leading to corrosion and alcohol's lower energy content. Older cars also are susceptible to damage to rubber parts. But in the case of the OP, I'd be running the 93 as that's the recommended fuel by AM. With 91 actually being the minimum. Lower ratings, under load and heat, will pull timing and lose power. Under 91 and the ECU may not be able to pull enough timing to mitigate detonation.

@ about 8:00 Ian talks about ethanol in classic cars.