brillo

I have searched the internet and I can't find a good explanation for this. I would think the 93 octane like we get in texas would be better for emissions purposes for engines that can use it. What gives?

RevTo9K

MTBE, an additive, was banned in Cali, and after that 91 was the max. Why they can't currently get better than 91 octane without it, I'm not really sure.

MazdaManiac

iTrader: (3)

So why does Arizona only get 91 and we still have MTBE?

Detroit RX8

They are afraid it might spontaneously combust in the heat

Might have to do with supply since you are along the distribution to Cali you get what they get?

truemagellen

A lot of the Octane ratings simply have to do with Altitude

for instance...in Cape Town, SA we were buying 92 octane as Regular and 94/95 as Premium

if you think I know the science behind it for get it :-p

BlueEyes

They can still make it. Califonias CARB standards make the production of high octane fuels expensive, especially because of how much cali would use. As well, I think that some oil company holds the patents to making CARB freindly high octane fuel, and they would need to get royalites from any other company that makes it.

MikeW

But that AKI number is (not R + M)/2 research / motor.

Usually the R number is five points higher than the AKI average number.

BunnyGirl

I am pretty sure the Chevron I buy here is 92 although I have seen lower for octane for "premium" here at 91. I am pretty sure a lot of it has to do with altitude. I remember going through the mountain areas on I-90 through Idaho/Montana and regular was 85 octane.

playdoh42

I read an article in motortrend that said the reason why Cali only have 91 octane fuel is due to the disporportionate amount of luxury cars and sports cars that require high octane fuel. They have a base amount of crude that they can use to make different grades of fuels.

There are less porpotion of luxury cars on the East Coast so demand for premium gas is lower, therefore they can make higher octane gas.
In california, demand for premium is extremely high, they dont have enough components to make enough 93 octane to satisfy all the demand, so they make 91 instead.

they can make a lot more 91 octane fuel with the same amount of crude than 93 octane.
Im going to see if i can find the article for you, its kinda old, so well see....

playdoh42

Technobabble: February 2001
The Octane Game: Californians just got screwed. Hard.
By Dave Coleman



Dealer Locator

Discount Pricing
Gift Subscription

Subscribe Now



By the time you read this, residents of Nevada and Arizona will have been screwed too. What, you don't live there? Just wait, you're next.
It's not like West Coasters haven't been screwed before. From roadside smog dynos to tickets for shiny mufflers, we're used to the man getting us down, but this time they're hitting us where we eat. This time they're taking our gas. We already have pretty crappy premium fuel in California. Just like most of the West Coast, we're stuck with 92 octane, while much of the Midwest and the East Coast got to play with 93 or better. Now, as of August 1, 2001, the best we can get is 91. Time to turn down the boost.

On the off chance you're only now trading in your Schwinn 10-speed on a twin-turbo Supra, I guess I should stop here and explain what octane is and how it affects your engine.

When fuel is injected into the cylinder, compressed and ignited, one of two things can happen. It either burns quickly and smoothly, shoving the piston down with a strong, even push, or it explodes all at once, releasing its energy in a sudden burst of heat and pressure. This explosion is called knocking or pinging, and it's something engineers like to call "really bad."

Knock is usually ill timed, occurring early in the combustion cycle when the crank and rod are still straight up or even worse, still trying to complete the compression stroke. As a result, all the energy released slams into the top of the piston without actually turning the crank. When this happens under stressful enough conditions--like, 20-psi of boost in a Miata--you start breaking things. Usually the ring lands; however, if your pistons are strong enough, you might get lucky and blow a head gasket.

Octane, for those of you still on the bike, is the rating of a fuel's ability to not do this. The higher the number, the less likely the fuel is to detonate. What this means to us, of course, is the higher the number, the more boost we can throw at that Miata. High-octane gas isn't just for tuners though. Plenty of stock cars depend on the stuff, including a Celica GT-S with its 11.5:1 compression, or a turbocharged WRX or Volkswagen 1.8T.

These cars rely on high-octane gas to keep from detonating. Feed them 91 octane and they won't start breaking things, because their knock sensors will see it coming and retard the timing, turn down the boost or otherwise reduce your chances of having any fun.

Whose fault is it this time, CARB? The EPA? The CHP? None of the above. This time we're being victimized partly by the oil companies, and partly--this is the one that hurts--by ourselves.

You see, when crude oil is refined into gasoline, the refinery doesn't have all that much control over what comes out. Crude oil is full of all kinds of stuff, and a refinery simply separates it, sorting all the iso-this and hepta-that in order of density. The really heavy stuff, like tar, is near the bottom, while the really light stuff, like butane, is near the top.

Somewhere in the upper ranges of the stack are the components of gasoline. There are between 10 and 15 different blend stocks, each with a different octane rating, which are mixed together to make gasoline.

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.

In the Midwest, where an extensive customer base of good old boys in pickup trucks consume vast quantities of 87 octane, demand for premium fuel is low enough to make genuine high-octane premium.

In California, however, Lexus-driving executives suck down premium fuel like it's Evian, so 92 was the rule.

CARB isn't entirely innocent. Many of its standards for evaporative emissions and misdirected attempts at oxygenation have raised the manufacturing cost of high-octane gas, but it doesn't seem to be behind the sudden change to 91. Instead, according my super-secret oil industry mole, it all comes back to money. Unocal, you see, has a patent on the 173 easiest ways to make California-friendly 92-octane gas. As a result, every other oil company has to pay Unocal 5.75 cents for every gallon they make using one of these techniques. They haven't actually been paying it, but that's an issue for the lawyers to sort out.

Suddenly it's pretty obvious why our gas sucks, but why doesn't Unocal still sell us 92? Because it can't. In 1997, Unocal sold off all its 76 gas stations, and with them, its ability to decide what kind of gas to make. All Unocal can do now islook for oil, suck it out of the ground, and wish it had some way to make everybody else keep using its patents. You see, not only did Unocal screw us, they screwed themselves.

Ironically, the only gas stations in California with anything better than 91 octane are the ones Unocal used to own--the few 76 stations offering 100-octane race fuel. You can locate these elusive stations at www.76.com, but bring your wallet. The current going rate is $6.00 a gallon.

DOMINION

They are not the only one. We have a station right by our track out here with 91. All the N/A ricers fill up there its so

WRXtoRX8

thankfully I live right by a rebel that has 100 octane race full at the pump. interesting how are full price is always going up and down but the 100 octane stays at $4.99 a gallon. oh yeah and as the article states we only get 91 octane in vegas.

question
Does the rotary run better with the higher octane?

Moostafa29

Because the people in office are a bunch of tree hugging hippies with nothing better to do than to come up with all these rules and regulations to keep our emissions (POWER) to a minimum.

Japan8

NO. Search. Been discussed before.

Combustion chamber shape and issues with flame front propagation is why you have two plugs per rotor. Low octane fuel burns more easily, and faster than high octane fuel. The point of high octane is to make it difficult to burn so that in a high compression FI engine (like the MS3, MS6 and GTI) the fuel doesn't combust early because of the heat from the plugs or carbon deposits in the combustion chamber caused by the higher temp/pressure from high compression and FI.

MercXP

so, your saying buying 89 is better then getting 91 for an Rx8?

zoom44

i used toi say the same thing as above until a year or so ago when i got me some learnin

octane doesnt mean the fuel burns any less or more easy and high octane fuels (In general) burn more completly than lower octane fuels. it simply is a rating of how well the fuel resists UNINTENDED ignition. you shoul duse the grade of fuel that doesnt cause you engine to knock. this can change from area to area and time of year. use ahigher octane in summer and you can switch to lower octane in the winter.

here read this

http://www.faqs.org/faqs/autos/gasoline-faq/part3/

especially 6.2 and 6.3

which include this among other things