Another thing to keep in mind is just do the math: IF base stock was only 80 octane and pure ethanol is 113-115 octane and the gas is SUPPOSED to be 10% (I have seen it higher) take 10 gallons and do the math- 9 gallons of 80 octane, 1 gallon of Ethanol, now multiply 9x 80 =720, add 114 to 720=834. Ok , now divide 834 by 10= 83.4 octane. If base stock was 85 octane, 85 x 9=765 + 114=879 divided by= 87.9 When you buy 93 octane they have to boost the base stock to a MINIMUM of 90.5 octane BEFORE adding the ethanol even if they make up the complete difference with the full 10% ethanol, so you are still getting pretty good fuel when buying 93 octane IF its actually what they claim it is, Smitty

Never thought of it that way but it sure makes sense!! thanks for the Insite.

Smitty, I test the octane using an electronic scan tool, and your right it's not cheap ( $ 12,000.00). I figured if a set of 8 melted pistons cost $ 12K then I'll save myself some time and test the fuel rather than replace engines. I was sure fuel was the problem and I was sure the fuel companies were cheating me. I have yet to find any gas sold anywhere that is less than advertised on the pump. This scan tool also measure ethnol and generally ethanol runs about 8% but it does vary. The safety is built into the system because fuel pumps post the MINIMUM octane. I have never found fuel that is "minimum", lowers was .5 over and more often than no it is 1 - 1.5 octane over the posted minimum. Add water to the test sample, shake it up and the octane goes up as you might expect. Plenty of problems with mixing water and gas but as a detonation suppression it will increases "octane". I own lots of gas engines, weedeaters, generators, cars, tractors,boats, jets skis, chain saws and I would not want to run gasoline that is 2 years old and it probably will not even start, but I would be sure that the octane is ok.

So the comments I have read in the past that gas looses 1/2point of octane a month is not true?

10 points per Octane @ 1/2 point per month loss will work out to .6 Octane per year, thats not too much to get excited about but my test over 2 + year period show 0 Octane losss based on time.

There is a big difference between gas that is freely vented to atmosphere vs sealed. If you have 10% Ethanol gasoline and it is vented to atmosphere over time because the ethanol is so hydroscopic it can attract moisture and if it gets enough it will phase sepearate leaving behind base stock gasoline and watered down ethanol, not good. This is much worse if it is exsposed to direct sunlight or large heat swings. will the gas go bad in this kinda storage, sooner or later. Will its properties (including octane) get screwed up once it gets water in it and it phase seperates, yes.
On the other hand-if it is in a sealed container (like a 55 gallon drum capped tightly) and not exposed to wide heat swings it is safe for alot longer than you could imagine. We just pulled a sample on some E-85 that I had left from dynoing a street motor 13 months ago , it has been sitting in a sealed drum 95% full, there was no "extra" water in it when we tested it and my son ran all 50 gallons of it in his Grand prix at 14 lbs of boost with no issues.

Nice, I looked at them online for 10,000$ a few years ago and never bought one, Smitty

$10,000 well thats out of my leaque, but it is reasuring to know that the octane level is as posted. I have not had a problem with the 93 octane yet! Thanks for all the information.

This is a very good thread, since there is so much crap out there on the subject. James, that tool has to have some rot and tired sensors, probably doesn't come with a trailer, and the carrying case vinyl is probably cracking...will $120 work for you? What's a couple of zeros between "friends", I'll even pay the ride ;)

I read a article in the detroit free press a few years ago that said at least 10% of the metro gas stations and a smaller but still signifigant% of mi stations sell lower octane gas in their tanks than marked to make extra money and because IF they do get caught the fine is far less than the extra profit. The independent stations were the very worst! I also read the state is terribly under-manned in the bureau of weights and measures dept and they check very few stations posted octane vs actual, more concerned about pumps that under-deliver on volume. I think with modern pumps this is less of a concern though. In the 90's I had 2 daily drivers that were octane monsters, a 84 chevy 1/2 ton that had a zz4 crate motor that I had quickly broken the factory hypertectic pistons in and a 69 grand prix with a pontiac 400 with 10.75-1 compression. The truck had 58cc vette heads that were milled even further with porting, I could tell you back then every pos gas station that lied about there octane because IF I didn't get true 92 or better it rattled and there were some stations that it rattled like a can full of marbles after buying gas from that I avoided. The Grand Prix was the same way, if I got anything less than 93 octane I had to get timing light out and retard the timing or it would knock too. These days I try to buy all my gas from stations that I have tested the ethanol content at and have found in Mi for the most part that Shell and Bp have the best premium, Smitty