Gasoline octane

I realize the owners manual specifies 91 octane, minimum. However, modern engines have knock detectors and will retard the timing to accomodate the lower octane, e.g 89. I also realize that retarding the timing will diminish performance. The question is: will a lower octane, say 89, cause engine damage. BTW, I have always used 89 octane in my '04 V8 and haven't heard the suggestion of a "ping."

No, no damage. Like you said, that's what the knock sensors are for...

You may want to get a good mileage reading after several successive tanks of each, though. You may not be saving any money due to the lower mileage. I've never tried to run 89 consistently. Besides, mine pings under light throttle (too much "vacuum" advance and I'm too lazy/busy to retune it despite the fact that I've og thte tools!) on 94.

I've logged about 8,000 miles on the car and have consistently got 23 to 25 mpg. Granted I live in a rural area and only occasionally venture into the city,but I still think the mileage is very good. BTW, at a steady 70 mph, I average over 26 mpg.

Anyone ever try running an LS on ethanol (E85 or otherwise)? I assume the answer is no as it seems like a pretty big risk, however there are quite a few people in my family (who drive less sophisticated cars - IE. an 94 Chevy 1500 pickup) who are willing to try this to save a buck.
There are/were also kits on ebay for converting regular vehicles to ethanol that go on the fuel injectors. This seems like an even bigger risk considdering the LS's engine computer, but I thought I'd mention it.
Oh, and thanks to everyone with all the help. I've had almost every problem listed on this forum at one point or another and I've never found a question without an answer.

Up to 10% ethenol is ok. E85 would cause damage to your cars fuel system if used on a regular basis. Not worth it in my opinion. Plus E85 yields lower gas milage, so why bother?