Octane Confusion
 

Found this on Mazda's site "Maximizing Fuel Efficiency: Use a high-quality fuel with an octane rating appropriate for your vehicle, and use the lowest octane possible. "

Thought the higher the octane the better?

Generally speaking, you only need to use an octane that is high enough to prevent detonation - anything higher than that is a waste of money. The octane rating is roughly inversely related to the ignition/burn rate - lower octane burns earlier/faster which leads to pinging/detonation more readily for high compression engines, or for engines with more timing advance. However, if your engine doesn't detonate with the lower octane, you'll feel a little better "kick" with lower octane. I know that I could tell the difference in a couple of my previous vehicles. It is harder to tell the difference in newer, computer controlled engines because they'll detect knock if it occurs and will retard timing.

In the 8, I've switched to 87 for most tankfuls, and it runs great. I haven't had any detonation (which sounds llike popcorn popping in the rotary). I run 91 every once in a while to get the extra cleansing/detergent benefit.

I have been using 85 octane gas on my 8 as there is nothing else available where I live. Don't know what the long term effect will be, but so far the engine runs as smooth as anyting. I was using the same fuel on my previous BMW with no ill-effect.

So you guys that have run 87 octane are saying so far it's been pretty safe ?

I had been running 89 and 91 octane for the first three tanks and have been getting around 15 mpg. I ran 87 octane on the last tank and got by far the worst mileage since I bought the car (12.75 - mostly city driving and 3-4 mile commute). I'm not saying it's octane related, but I switched back to 89 for this tank to see what happens. Hell, it could just be my lead foot now that the car is broken in, but 12-13 mpg sucks arse!!

I run 87 octane and get 17-18 city and 20-21 hwy.

They have less cleansing in 87 octane? I think the cleansing/detergent benefits is another myth of higher octane gas. They only real difference between types of gas is the octance added to it.

Yeah, you are probably right on that too. It depends more on the brand though, because all of the base fuel comes out of the same pipeline - its only the additives that the end manufacturer adds that differentiates them.

I use only premium 93octane and I was geting 14-16 miles. Now I switch to 89 and will see....

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Originally posted by flatso
They have less cleansing in 87 octane? I think the cleansing/detergent benefits is another myth of higher octane gas. They only real difference between types of gas is the octance added to it.
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You can't "add" octane to a gasoline the way you can add detergents. A refinery has several process units that make gasoline components of various octanes. The higher octane components are generally more expensive to produce. The way you blend these together determines the octane of the end products. You have to use everything you make, which means that all the process plants operate to just the degree of severity necessary to produce enough octane pool to make all the 87, 89, 91, 93 octane gasoline you can sell. After you add the government mandated oxygenates, the final octane of each product is what it is. There is no secret sauce that turns 87 octane into 91 octane gasoline.

Yes you can.......... Yes there is, it's called Xylene. Run a search on it, you'll find a lot of info.

Symantics. Xylene is an aromatic that is a component of common gasoline. It's part of what makes a 93 octane gasoline higher octane than an 87 octane gasoline. There are safety and environmental concerns to high aromatic gasoline which is why the stuff you pump at the ordinary station doesn't have as much of it as it used to. The point is, xylene is just a high octane gasoline and when you put it in your tank it blends more or less volumetrically (actually, that's a wierd science) to boost the octane. It not a magic bullet additive where a few teaspoons gives you 3 octane boost.

There used to be just such a magic bullet called TEL. But, then, all the kids that lived beside freeways started life with lead poisoning so we don't do that anymore either.

Secret Sauce.....
 

Bernie is right, (and seems to know of what he speaks - 'octane pool' and 'process unit severity' are not everyday terms unless you work with them daily.....) The refinery only runs their 'crackspread' hard enough to meet the demand, and minimize 'giveaway'.

Now that lead additives are in the past, you pretty much have to 'build' a good gasoline, from the ground up. Obviously, Xylene will add a quick octane boost to make 'racing fuel', but if you have low octane to start with, you are pretty much screwed. Some components of the base gas have octanes in the '70's'

Flatso is also correct, a tank of 'SuperDuper' once in a while will keep everything nice and clean. Shell only puts their best cleaners in the 'Optimax' brand, which is usually the top octane level. The other grades, and the wholesale stuff, just get enough to meet the standard.
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doc

93 premium