What grade of fuel works best for you?

You've described preignition, not detonation. They're two different things. Detonation is uneven spread of the flame front and occurs AFTER spark ignition. But you are correct that it is detonation that causes pinging. Unlike detonation, preignition often causes serious engine damage.

 

Don't today's engines have detonation sensors that automatically retard the spark if detonation occurs?

 

What is your opinions of gasoline/ethanol (90/10) in the Prius? Advantages? Disadvantages?

I have been using 10% ethanol 89 octane, (midgrade) since I purchased the car but I am only on my third tank because I just took delivery 2 weeks ago. The first tank was purchased by the dealer so I am not sure what it was, probably 100% gasoline 87 octane.

John
'05 Silver, option 6, (mud flaps, EV, auto locks on order.)

 

http://www.hastingsmfg.com/Service%20Tips/...preignition.htm

Interesting article on detonation/preignition

 

If you provide a page #, I can post it.

 

I see no reason to deviate from the Toyota recommended fuel, so I have no "experience" at other grades of gasolene. There are so many variables in "mileage" that it would be difficult, if not impossible to document differences.

Due to varying "additives," I do plan to switch to Shell since some posts have reported better mileage using Shell gasolene. Still, it may be hard to really note any difference.

 

I have now created a FAQ entry for this assembled from the helpful and informative posts by the many here.