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Discussion Starter #1
The swami has been hearing a lot of nonsense around the gas pumps these days. People are tanking up with the "good" stuff because the commercials imply that it's better for their engine. When the oil companies use superlatives like "Super", "Extra" and "High"...well it must be better, right? And of course they wouldn't be charging $0.10 - $0.20 more unless they were putting some really good stuff in there, right? Sorry...NOT!


"High Octane" is not synonymous with "good" or "better", and does not mean that it is better for your engine! And the chances are pretty good you don’t need high octane fuel in your scooter.

High-octane fuels only become necessary when your engine has a high compression ratio. It’s a very long and complicated story…that the swami will make short.

First important fact that you must accept:

All gasoline, regardless of its’ octane rating, have pretty much the same amount of energy per gallon. What!!! "Sacrilege" you say? Well, actually, some higher-octane fuels have a few LESS percent energy per gallon…so as not to argue over this small point, for the sake of this discussion we will all agree that the automotive gasoline that you buy at the pump, regardless of octane rating, has the same amount of potential energy.

Second important fact that you must accept:

Octane is NOT a measure of power but of the fuels’ resistance to ignition from heat. A higher-octane fuel also, under identical combustion chamber conditions, will burn slower.

How can this be? If all of the above is true, how do we get more power out of high octane gasoline? We do, don’t we?

Well…yes we do. Here’s how:

But first you must understand "heat of compression". There is a 2,000 year old fire starting device that still amazes the swami. A length of bamboo was hollowed out leaving one end capped. A stick, about the same length as the bamboo, was whittled down until it fit snugly into the bamboo cylinder. A bit of dried grass or wood shavings were placed in the bottom of the bamboo cylinder and the snugly fitting stick was violently rammed down the bamboo tube. The heat generated from rapidly compressing the air in the tube was sufficient to ignite the tinder.

The same thing can happen in the cylinder of an engine. The piston, quickly squeezing the fuel/air mixture into a small space, can generate enough heat of compression to ignite the fuel well before the spark plug fires, with unpleasant results. If the fuel prematurely ignites while the piston is on its’ way up, the burning of the fuel, in conjunction with the rising piston, creates even more pressure, resulting in a violent explosion. This explosion is equivalent to hitting the top of the piston with a very large hammer. If you want to be able to see through the top of your piston, ignore those sounds that are usually called: "pre-ignition", "ping" or "engine knock". Trust me on this one; in his reckless youth, using this method, the swami turned a few pistons into paper weights.

What we really want is a very rapid burn of the fuel, not an explosion. And we want the burning of the fuel to take place while the piston is in a better position to convert this pressure into productive work, like on its’ way down. Think of this burning as a very fast "push" on the top of the piston. Despite the violent noises you hear from some exhaust systems, it really is a rapid push on the top of the piston making the crankshaft go around, not explosions.

So that we can ignite the fuel at exactly the right time with the spark plug, instead of from the heat of compression, they put stuff into gasoline to keep it from igniting prematurely. The more resistant the fuel is to ignition from the heat of compression, the higher its’ octane rating.

Are you with me so far?

Higher compression ratios = higher combustion chamber pressures = higher heat… and it is with these higher combustion chamber temperatures that the magic happens.

At higher temperatures the fuel is burned more efficiently. So, while it’s true that the higher-octane fuel does not posses any more energy than low octane fuel, the increased octane allows the extraction of more of the potential energy that has always been there. Conversely, lower compression ration engines utilize a little less of the fuel energy potential (2-4% reduction) but there is also less heat generated in the combustion process.

So how do you know if you need high-octane fuel? The swami suggests you look in the owners’ manual! Manufacturers really do want you to get the maximum efficiency out of your engine. They do their best to give a good balance between horsepower and engine life. It’s in their best interests to do so.

There is ABSOLUTELY NO BENEFIT to using a higher octane than your engine needs. The only benefit is increased profits to the oil companies that have cleverly convinced some of the public that their new "Super-Duper, Premium-High-Test, Clean-Burning, Used-By-Famous-Racing-Types-All-Around-The-World, Extra-Detergent-Laden-Keep-Your-Pipes-Clean, Extra-High-Octane" fuel is your engines’ best friend. The swami is telling you the truth, don’t listen to that talking cartoon car.

The swami hears people insisting that they got better mileage, better acceleration, and less dental plaque by switching to a high-octane fuel. The swami reminds these people that in every pharmacy is a special miracle pill that is often prescribed by doctors, it works wonders because people believe that it works wonders; it’s called a "placebo". The swami warns: never confuse faith with physics!

If you are getting pinging or knocking with what should be the correct octane for your engine, start by checking the ignition timing, also check that the spark plug is the correct heat range. For 2-strokes, check for excessive carbon build-up on the top of the piston, the carbon takes up space and increases the compression ratio.

If all is well and correct, and you still are getting knocking, then try the next higher octane. You won’t go faster, you won’t go farther, but you will prevent an unsightly hole in your piston.

This subject is a whole lot more complicated than the swami wants to bother with. If you are curious to know more, put some of these words into your search engine and enjoy the education:

Antiknock Index

Octane

Stoichiometric Combustion

Thermal Efficiency

Flame Front

Highest Useful Compression Ratio

Compression Ratio

Placebo
 

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sticki!
 

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Discussion Starter #4
well hope this will clarify things a little bit for everyone
 

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week by week comparison:

week one on 89 octane = 32.xx MPG

week two on 92 octane = 29.xx MPG

week three on 89 octane = 33.xx MPG

week four on 92 octane = 28.xx MPG

after that I will only put 89 in my car. By reverse scientific thought, if anyone out there has 20 octane, the car will get 300 MPG and be super fast lol.

Seriously, the car acted better on the 89 then the 92. It did not seem to run better, but it just felt a little more alive on the acceleration part. The mpg was better. This was the same car, same average temp, same average driving style, etc etc. Same schedule for my business, everything was the same that could be.
 

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Discussion Starter #6
On that same note, you will not wreak any benifets from driving on high octane fuels especially not with gas milleage

On my recent trip to OKC Tunerfest here from Sachse TX which just so happens to be a 3.5 hour drive i managed to maintain a gas milleage of 50 mpg + and got over 500 miles on a single tank running on 89 octane...

Fuel additives such Octane Booster and NOS Racing formula with Nitro Methane are mainly to help decrease the chance of detonation on high compression engines such as turbo charged, super charged and also those with high compression pistons... These are cars that will actually see a performance Gain by using a higher rated octane rated closer to what their car needs...


Higher octane IS NOT like nitrous shots in which the detonation Power is increased but simply pre-detonation is decreased. If you want to get more power out of your engine without major modification, rather than running higher octane, just get your self a bottle of nitrous, or if i may borrow a quote from a famous source "I need two of the big ones" and blow your engine seals to high hell.......
 

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I know it doesn't help but it's just easier for me to put super in my car because that is what my bike calls for. It's just easier for me to say it when I'm at the pump.
Now you might say I'm throwing my money away but I don't smoke, don't drink and I'm married and go out on occasion.
 

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If you're going to post stuff like this, a source would be nice.

[edit] also, its not necessarily true that you're throwing money away on higher octane. Typically the highest octane available at the pump also has the highest level of additives and such to help your engine run cleaner. Running a tank of high test would be the same as running a bottle of fuel system cleaner in this case.

Also, some testing done by showroom stock racers has shown that certain cars can and do benefit from higher octanes, even when they call for the 87 pee water that most of us use. Some cars gained 1-5 horsepower with 93 octane, some lost 1-5 horsepower, and most couldnt stand race gas (100+ unleaded) and lots 5-8hp. It depends on how flexible the stock ecu is.

[Edited by skierd on Oct 12, 2005 9:32 AM]
 

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I agree, I drive around around all day delivering pizza in an area that allows me to get upto 50 on the street. I've been experomenting with differnt types of fuel for the past couple of weeks. After a while of driving on 93, I put 89 in and could feel a significant difference. And in those instances using 93 I got better milage because I could accelerate easier. call me crazy.
 

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Discussion Starter #10
Originally posted by atullio
[body]
I agree, I drive around around all day delivering pizza in an area that allows me to get upto 50 on the street. I've been experomenting with differnt types of fuel for the past couple of weeks. After a while of driving on 93, I put 89 in and could feel a significant difference. And in those instances using 93 I got better milage because I could accelerate easier. call me crazy.
[/body]
You is crazy :chinese:
 

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My car actually gets around 35 with 93, and only 29 with 87.
 

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Discussion Starter #12
on my trip to OKC Tuner fest from garland Texas i got over 50MPG on 87 octane at a constant speed of 70 and occasionally faster.. I can swear that needle didn't hardly move for like an hour or so
 

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My numbers were both with the same driving conditions. My car really does better for mileage when I run 93, but it's too expensive to run all the time. I can't get my mileage much over 30 with the 87, but it easily does 35 on 93.
 

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Oh, right, this should probably be in the n/a forum. Moving...
 
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