91 Octane: hard to find in US?

I saw a couple of spec sheets that said the 76 100 octane unleaded was 106 RON and 94 MON. I believe pure iso-octane would be 100 each.

It seems to be have been sold under a variety of names, including "76 100 Octane", "76 Cool Blue 100 Octane", etc. The following lists "100 Octane Unleaded Racing Fuel" by ConocoPhillips as an EPA registered fuel:

In modern fuels, the octane rating is really AKI (anti-knock index); the fuel's resistance to detonation. The way they do that is by a process of oxygenation. This gives it an equivalent rating to some percentage of octane (the hydrocarbon). Its how they get octane ratings above 100 (which is equivalent to 100% octane in the fuel). The oxygenation additives they use in the US are not legal in Canada. The additive we use in Canada are very much more expensive. So, while there is nothing in 93 that isn't in

91, there is a lot more of it and it drives the price up.

Its not slower burning, it simply resists detonation on compression. Once burning, high octane burns just as fast as lower octane fuels

I'm not a fuel expurt so don't sue me but:

When lead was phased-out of US gasoline ('73-'75), MMT (methylcyclopentadienal,manganese,tricarbonal) took it's place as the primary octane-boosting additive. MMT has since been phased-out in the US but is still used in Canadian gasoline.

MMT has a nasty habit of growing rusty red deposits on your plugs and when used in sufficient quantities can cause fouling. Some OTC octane-boosters in in can are loaded with MMT. It's every bit as toxic as lead.

US gasoline has been leaning towards achieving the higher octane numbers by blending-in aromatics (xylene, toluene, etc.) The oxygenating components (MTBE, ethanol, methanol) have secondary effects of increasing octane and lowering the specific energy content. -Danny

BTW - AKI is the same as (R+M)/2.

You made it sound like 93 octane fuel would have to be astronomically expensive in Canadian. Perhaps marginally more, but not 2-3X times the price like racing fuels. If oxygenates are needed to boost the octane rating, ethanol is legal and used in Canada. 93 octane fuel could also be made without oxygenates. If there's any reason why you can find 93 octane in the NE US and not in Canada, it's more likely than not a business decision. When the pumps in California's major brand name gas stations went from 92 to 91, it was also a marketing decision.

I'm guessing the "additive" you're referring to is MTBE, which was supposed to have been phased out in California by 2002. The deadline was extended to 2003. The spec sheets I saw for the 100 octane 76 racing gas says it contains MTBE. I don't know if any equivalent product uses MTBE. Possibly not. I think the petroleum companies liked using MTBE in fuel because it's a byproduct of refining. Blending it in fuel was an easy way to get rid of it.

93 octane "super premium" is recommended for the WRX STi.

There are all sorts of strange marketing decisions in play. A few years back, all the name brand premium pumps were relabelled as 91 octane (R+M)/2 when they had traditionally been 92 for as long as I remember. There were article about "Where did the octane go?" It was a marketing decision that gave the producers more freedom to make higher octane products with what they didn't divert to the premium fuel production. It might also have given them an easier way to make fuel without oxygenates if the need arose.

Back in the 80's, Unocal 76 (before Tosco) sold an 89 octane unleaded in California competetively priced with other brands of 87 octane unleaded regular. They didn't carry 87 octane unleaded. They had a 92 octane premium, and some stations even had "Super Leaded".

Y'now what? I forgot to add, "in California.....". :)

This discussion is fascinating, thanks!

I should clarify that while 87-89-91 is the standard at most stations, Sunoco sells four grades, going up to 94 I think. In fact 91 isn't one of them, maybe it's 87-89.5-92-94? Not sure. Since it would require driving up to the pump (recall that the stations here only post 87 prices on the big sign), I've never compared 91 at Petro-Canada to Sunoco's 92 (or whatever my Forester's minimum would be) to see if there's a significant price differential. Now I'll have to, I guess. :)

And there's another brand with a "Magnum" gas that's either 94 or 96, I don't remember.

andrew [ snipped-for-privacy@wwwebbers.com]

I've never seen 94 (R+M)/2 octane on a pump before. I'm curious as to what WRX STi owners make do with in Northern California - 93 octane "super premium" is recommended.

87-89-91 is what we currently see in California. Used to be 87-89-92 as far as 2001. Apparently it was a choice of the oil marketers. Here's an article on the subject:

This is the interesting part, and it involves some math:

"The crude oil being used and little else determine the amount of each blend stock available for mixing. Generally, if you just dump all the blend stocks into a bucket, you end up with something around

88 or 89 octane. If you're selective and only mix the good stuff, you can make 92, 93 or even 95 octane. But once you take out the good stuff, you're left with crap--something like 85 octane. Then you have to leave enough good stuff in the bucket to bring this pee-water up to at least 87 octane. This limits the amount of 95- octane gas you can make. If you make 93-octane premium instead, you use up less of the high-octane stocks, allowing you to make a higher proportion of premium fuel." ** end quote **

So basically, they want to be able to blend what they've got into enough "buckets" to meet the demand for premium, mid-grade, and regular. A 92 octane premium meant they had to divert more of the higher octane blend stocks to premium, and might have eventually had excess lower octane blend stocks that they didn't have enough higher octane stuff to turn into 87 octane regular. So the answer was to lower "premium" to 91 octane and save some of the higher octane stuff to being the "pee-water" up to "regular" octane.

BTW - most of the off the shelf "octane boosters" aren't worth it. If it claims that it can boost the octane rating "up to 10 points", read the fine print that says that 1 point = 0.1 octane rating.

Octane booster. :-)

And yet, a few bottles per fill-up might just be necessary if you're in an area where there's only 91/92 octane available. :(

The jist is that many of these things are a high octane blend of one or more solvents. The "up to" probably refers to more "points" boosted if you're starting off with lower octane. Let's say this stuff is xylene (I've heard some of it is) with an (R+M)/2 octane rating of

116. Add that 16 oz bottle to 10 gallons, you get the following assuming linear blending of octane rating: 85 octane -> 85.38 87 octane -> 87.36 91 octane -> 91.32 100 octane -> 100.19

Some of these aftermarket additives contain MMT. There's only so much that can be in your fuel before it starts having a detrimental effect of your fuel system. There might already be some in the pump gas. Berryman has a line of octane boosters, and the one that boosts more octane isn't recommended for any cars with oxygen sensors or catalytic convertors.

We used to have some leaded race fuel available to the "cruisers" here in the Detroit Metro Area called "Turbo Blue" that was listed as R+M/2 = 104. Just a little bit in the palm of your hand would evaporate coldly & quickly not unlike a solvent ...even had a bit of a sweet ketone smell to it or something.

Aside from the good octane number, it ran really crisp in "cammy" motors that normally tended to stumble and hesitate on the standard-fare premium no-lead. It had really good vaporization in the intake manifold or something. I haven't seen it in a while.

Moving up one octane grade (about 2 pts.) shouldn't cause trouble, although using the recommended octane is recommended. If your vehicle requires a higher octane than recommended, it has a problem. Either a timing error or cylinder deposits.

A few times a station was out of the 87 octane my car requires, I refused the 93 octane they offered me at the same price. Operator thought I was silly, they just showed their ignorance of octane.

Since 1989 I've had perfect success with Chevron, no injector cleaning ever required over many miles. I moved to Chevron at Chryslers suggestion after Shell's additive for leaded fuel requiring vehicles fouled up my '87 vehicle's throttle barrel injector twice. There was a problem with Shell's additive in our winter climate which results in water in the fuel. Most Shell stations here shut down after their serious additive error.

I don't have the details in front of me, but there was consistently a

9c-10c difference between grades, which at most stations was 87-89-93.

At Sunoco with four grades, it was typically 87-89-91-93, with the 93 being 10c more than 89, as normal, and 91 being 1c or 2c less than 93 (it was 1c less in Plattsburgh on the way down, and 2c less in Albany on the way home). Encountered one full-serve Sunoco on the NJ turnpike with 87-89-93-94, I took 93 but did see a Porsche Turbo filling up with 94.

=aw andrew [ snipped-for-privacy@wwwebbers.com]

Most NA vehicles with the base engine take 87 octane- Chrysler 2.7L V6. The slightly hopped up engines take 89 octane- Chrysler 3.5L V6. I believe Volvos take at least 91 octane.

My wife's Sybring 2.7L V6 takes 87 octane for 200HP giving very good acceleration in that car. Her brother's Volvo 60, 2.4L with turbo takes 91 octane for slightly over 200HP giving similar acceleration and fuel mileage, but 91 octane is 15 to 20% more expensive than 87 here.

European cars suffer from tax laws based on engine displacement, so they build smaller engines and hop them up more.

When they say "points" they're not talking hundredths, they're talking tenths at a minimum. Also, you're forgetting that a bottle of octane booster may not act purely in an averaging capacity. A small amount may in some cases act far beyond what simple averaging would do.

Otherwise, those scientifically empirical tests of octane boosters when the booster is only in a 16 oz bottle wouldn't increase the octane value by 2-4 actual AKI.

That's race-track- or offroad-only booster. Unless the government in your area is braindead, they doesn't allow products like that to be sold at your average gas station without clear and obvious labelling. The STP additive, which is what is sold in the Canadian stores I've been to, is clearly stated to be safe for catalytic converters and oxygen sensors, and contains no alcohol.

This isn't true. My old 80s boat car, in the final years before I bought my STi, wouldn't run smoothly on anything but 94 octane. It was old, crappy, had serious problems: and 94 octane made it run nicer, with less knocking.

Recommended by who? Your implication by ommission is that higher octane is

*not* recommended by car manufacturers. I'd love to hear which ones state that "only octane of this value is recommended. Higher octane is not."

This is the part where you explain how the higher octane is somehow bad for your car.

I believe that I did mention that the Prestone octane boost products are labelled as "1 point = 0.1 octane rating number".

Depends on the product. Tetraethyl lead will boost the octane rating of any gasoline. Its octane boosting capabilities aren't from "blending octane".

My only point was that it's generally less cost effective to spend (in US dollars) $5 to boost 20 gallons of 91/92 octane than to buy marginally more expensive 93/94 octane fuel if available. Some people are even silly enough to use this stuff on regular unleaded when mid-grade or premium are available.