How Low Octane Will You Go??

I moved this post. I realized that I was hijacking another great post, so I moved it for courtesy and clarity.

Now, how low will you go??
Here is the reason that I ask. 93 octane, here in Kentucky, is Premium, with 10% Ethanol added. That same premium, without the Ethanol is listed as 91 octane at some stations, and 90 octane at others. I've polled the tanker drivers, and they all say that premium, is premium, and that all mogas in our area comes out of the same pipeline in Nashville TN. One driver I talked to told me that each retailer adds their own additives. One example being Shell, who he claims adds butane as a cheap filler. He also said that Ethanol adds 3 points to the octane rating. It sounds like the retailers are not all using the same measuring stick. I have several sources for Ethanol Free Premium, and I would love to use it, but I have been shy about using it, because of the questionable accuracy of the measurements. It looks like the highest octane that you can get from mid range mogas is 89. That being said, anything 90 octane, or above, must be premium. I know what the book says, but.... Any thoughts out there?? Would you run the 90, or 91, and feel comfortable with it?

Tom

For me personally, 91. Better to usually stick by an MFG's recommendation.
Could 90 be okay? Maybe? If you didn't get near a detonation scenario then it would be okay, but no one ever knows when that moment might come. Too many variables that could happen in a moments notice and I have seen 912's with detonation. It isn't pretty and can cost $4500+ on just one cylinder.

Is it worth the risk, not for me and if I have detonation and a gas station said it was 91 and you had it tested after an incident and it was only 90 or less then you might have some recourse.

Don't forget when this happens you are also going down and may not like what's below you.

Aren't you good to go with the 93 with ethanol? If so use it. Many of the Rotax LSA aircraft fleet in the US use 91 with ethanol and don't look back.

Roger, 93 w/ethanol is what I use at home. My primary reason for asking is that when fuel is needed away from home, not all airport mogas is 93. I see some 87, some 90, 91, and 92. I just wondered where to draw the line, or if they all used the same yard stick. My minimum number will be 91, ethanol, or no ethanol. Thanks for the reply..............Tom

Ditto. Around here we can find 91 AKI without ethanol. (I Jerry-can the fuel.) But the nearby place that had that closed, so it is a longer trip. I have no fear about running the Rv12 on 91AKI with ethanol. (They have more than here in Brazil y'know!) I like having the NO ethanol also for my 4 wheelers, lawn mower, etc where I think it DOES make a difference!

If you really believe one vendor can blend more of an element like Butane in than another, you should read this on how gasoline is formulated. ALL gas has as much butane in it as the refinery can get away with:

http://eprinc.org/2009/06/a-primer-on-gasoline-blending/

Butane has an octane that is about 93, so you shouldn't be worried about it at all just because it's "cheaper." Your engine would run great on that if you could run straight butane.

Thanks Ian. Great link with good info...Tom