Octane question (FOr the octane Savvy)

Ok folks I am sure this one has been beaten into the ground many times. However, I am now on a quest. Sort of. A friend of mine had an interesting
view to share on the topic of 87 octane vs 91 octane (low vs high) Below is his response to my statement (which is below his). For the record, he has a Nissan Sentra, Spec-v, his wife has a Dodge Noen (both run 91) I have a Dodge Dakota, and the bike I was referring to in my post was my old Suzuki SV650s. (I run 87 in both, as per their owner's manuals)
Does anyone happen to know where I might find, in writing, on a fuel company's web site that states that the only difference is the octane rating, and NOT the detergents? (or proof stating otherwise) I will be researching as best I can during the weekend, but any direction would be appreciated.
------------------------------------------------ Yes, i've read some very very extensive articles on gasoline octane. Here's a few notes:
- 91 will always run better than 87. - 91 from the different gas companies is all DRASTICALLY different - Running 91 on a car that doesn't need it WILL NOT damage the car. It will make it run just the same as what the car is tuned for, but it will allow an extra margin of safety from unpleasant car conditions (i.e. heat soaked radiator causing overheating, creating knock conditions, 91 will not require the ECU to compensate nearly as much or as early as if it was on 87) - 91 octane at most gas stations will contain extra detergents and cleaners which will prevent your injectors from clogging up as easy, keep the valves cleaner, and keep all related fuel lines/pump cleaner and free of debris. - 91 octane at 76 or Shell is considered the absolute cream of the crop for Southern California. The difference between these two and Cheveron/Exxon/Mobil/Generic brand is HUGE. Some stock cars are noticing a 5-15% power drop from just using the wrong brand of 91 octane. - For reference, your air conditioner will sap around 10% of your cars horsepower when turned on. - Also for the record, if you do the math with a 10-11 gallon fillup, thats only an extra $2 each time you fill up (1-2 times a week means an extra $8-$16 a month) for a cleaner engine and safer driving condition. Thats worth the extra cost in my book.
----------------- Original Message ----------------- From: Trey Date: Jun 3, 2005 4:18 PM
Have you actually read up on what makes 91, 91? or what the three grades do? If the car is not designed for it, the higher grade can actually damage teh car. My truck for example, it notes not to run 91. 91 can degrade performance in a car designed for 87. Some cars (like your spec-v) spec that it will run on 87, but to use 89 for best performance. In that case, the car WILL run on 87, but the knock sensor will retard the timing (reducing power) to keep it from knocking. and is able to advance the timing with the 89. I remember my motorcycle actually felt down on power when I ran 91, it actually ran better on 87. as for being "negligibly more expensive than 87" its about a .$20/gallon difference. Doesnt sound like much, but when your buying 20 gallons at a time, and get 12 MPG, it adds up VERY fast. Thats an extra $200 a year Im just blowing out the tailpipe of the truck.
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Gasoline FAQ - Part 1 of 4
http://www.faqs.org/faqs/autos/gasoline-faq/part1 /
From Sunoco http://www.sunocoinc.com/market/transportation_fuels.htm Octane
Octane is a measure of the antiknock quality of gasoline. The octane number posted on service station dispensers and listed in car owner's manuals is an average of two measurements: Research octane number and Motor octane number. These octane numbers are determined using a laboratory test engine operated at different temperatures and speeds to simulate different driving conditions. The average of these two numbers, (R+M)/2, provides an indication of on-road performance. Most car owner's manuals recommend a certain octane but advise owners to increase octane if they detect audible knock or unsatisfactory performance.
Many new vehicles are equipped with knock sensors to prevent engine damage resulting from knock or to enhance performance. When engine knock is detected, the knock sensor system retards ignition timing until knock is reduced or eliminated. When ignition timing is retarded, power and efficiency are reduced so drivers can experience poorer acceleration performance and gas mileage. These vehicles require a higher-octane fuel to provide optimum performance.
Sunoco has the distinction of offering a range of gasoline octane levels to satisfy the vehicle population. Sunoco produced leaded gasolines in the 1970s such as Sunoco 190 with 89 to 90 octane and Sunoco 260 with 97.5 to 98.5 octane. Sunoco's current unleaded gasolines include Economy with an 86 octane and Ultra with 94 octane. In order to provide this high-octane fuel, Sunoco has tested different octane enhancers over the years. These tests included oxygenated compounds (methanol, tertiary butyl alcohol (TBA), ethanol, methyl tertiary butyl ether (MTBE), isopropyl alcohol (IPA), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME)), metal-based additives (lead, methylcyclopentadienyl manganese tricarbonyl (MMT)) and aromatic amines.
Sunoco has produced leaded racing gasoline since late the 1970s and unleaded racing gasoline since the mid-1980s. Typical properties for these fuels are listed in Table 1. One of the unleaded racing gasolines, Sunoco GT100 is available at select Sunoco retail stations.
Table 1: Sunoco Leaded and Unleaded Race Fuels
--------------------------------------------------------------------------
Property Standard Supreme Maximal GT100 GT Plus
--------------------------------------------------------------------------
Specific gravity 0.725 0.715 0.700 0.760 0.735
Octane (R+M)/2 110 112 116 100 104
Research octane 115 114 118 105 109
Motor octane 105 110 114 95 99
Reid vapor pressure 8 8 6 8 9
Distillation
Initial boiling point 90 90 100 90 100
10% evaporated 160 155 150 150 135
50% evaporated 220 215 220 210 200
90% evaporated 260 235 230 230 230
Final boiling point 360 260 260 260 255
Lead Yes Yes Yes No No
Color Purple Blue Red Clear Light Blue
Oxygen
2.7 wt. 4.5 wt.
--------------------------------------------------------------------------
From the Staging Light Knock, Knock! Sounds of an unhealthy engine
Disclaimer: While based on facts about drag racing, this page contains the personal views and opinions of one racer - Michael Beard
Three weeks ago at Beaver Springs Dragway, Beaver Springs, PA, we used a higher octane fuel than the usual kind. Typically we use 93 Octane from Coastal in our Duster drag car, but we decided to try the much-heralded Sunoco Ultra, which is 94 Octane. The car ran exceptionally well that weekend, and it seemed that our fuel consumption had decreased. It seemed obvious that the higher octane provided the engine with more power and better gas mileage. Hence, you had to wonder what octane was really all about. First of all, what do the octane ratings mean? If you have ever been bored enough while filling up your car at the local gas station, you may have noticed the stickers on the fuel pumps. One of them indicates that the method used for calculating the octane number is (RON+MON)/2. The RON refers to the Research Octane Number, and MON to the Motor Octane Number. The two numbers are derived from different test conditions. The RON method represents normal mild driving conditions, while MON tests are done under severe conditions and high engine speeds. Sensitivity is the difference between the two octane ratings (RON - MON Sensitivity), and indicates how the fuel will respond under different driving conditions. Gasoline in the United States is required to have a high MON, thus keeping the Sensitivity number low. This is important because it means the fuel will operate consistently despite changes in driving conditions. Now, with some of the basics out of the way, we can ask some more interesting questions about octane. The formula (RON+MON)/2 is referred to as the anti-knock index. This leads us to ask exactly what knock is. A good description comes from E.F. Obert, in "Internal Combustion Engines and Air Pollution" (1973, Harper & Row). "During the compression stroke of a spark ignited engine, the pressure, temperature, and density of the mixture are increased and, depending on the fuel, chemical reactions ... may begin. The spark ignites the mixture, then the flame travels across the combustion chamber at a more or less orderly pace with the pressure rising uniformly throughout the chamber. Ahead of the flame front, the unburned mixture ... is compressed by the rising pressure, with an accompanying rise in temperature and density. ... If the ignition delay (chemical) of the end gas is consumed before the flame arrives, autoignition takes place. With autoignition, the orderly process becomes uncontrolled and a violent rise in pressure may occur. Energy may be liberated at such a rate such that the walls of the chamber ... vibrate, and knock is said to be present." The octane rating is the measure of the fuel's resistance to autoignition. When autoignition occurs the gas pressure wave it causes superimposes on the normal pressure wave of the combustion chamber. These two waves interact to create a third sawtooth-shaped wave pattern of pressure oscillations. The pressure oscillations create the knocking sound. Pressure waves caused by knock can build up quickly and shorten the life span of an engine. Knock can be reduced by adding chemicals to the fuel. Common examples are tetra ethyl lead, aromatics, and oxygenates. While these substances increase the octane rating, their composition does not contribute to the energy of the fuel when it is burned. The result may be less energy per unit volume of fuel used, and thus less efficiency. In short, higher octane fuels may require more fuel to be burnt in order to produce the same amount of energy. But wait! Didn't I say at the beginning that we experienced a gain in power and fuel efficiency? There is one piece of information we have been missing. The compression ratio of an engine has a lot to do with knock and the apparent effects of octane. Compression ratio can be thought of as the pressure in the combustion chamber. High compression ratio engines have more of a tendency to knock than lower compression ones. Given what we know, since a low compression engine is not as likely to knock, it does not require a fuel with as high of an octane rating. A high compression motor, however, needs more octane to reduce knock. In such a case, switching to a higher octane fuel would reduce the effects of knock, leading to a more efficient combustion process. This creates more power and better fuel economy. Using a higher octane fuel in an engine that does not experience knock will not help performance. In fact, if the higher octane was achieved through the use of oxygenates, higher octane than necessary may actually hinder the performance of an engine! The goal, then, is to find a fuel with an octane rating that is high enough to prevent knock, but not much higher. It is possible that the tiny performance boost we experienced with the drag car is related to the use of the higher octane fuel. The compression ratio of our motor may be a borderline case where it is able to use the slightly higher octane. Sunoco 116 would not help our relatively low compression motor any more than the Sunoco 94, but it is a necessity in most of today's extremely high compression race engines. In fact, at over $4.50 per gallon, Sunoco 116 would do nothing more than drain your wallet faster! Technology is not cheap. WARNING: Use extreme caution when attempting to use a fuel with a lower octane! If the octane you use is too low, knock will occur, and your engine can be damaged. Follow your manufacturer's guidelines as to what octane is suitable for your vehicle.
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This is in fact, false. A motor designed for regular may perform poorly with premium.

False.
In general, this is not true; if a motor has knock sensors and was designed to run on regular, it will not run any better or be "safer" with 91.

No. Chevron, for instance, puts the same amount of Techroline in all their gas.

Hard to believe; I doubt it on general principles. If you can find anything but anectdotal evidence I would be very surprised.

If you're talking a 4-cylinder 150hp engine, yes. They take 10-15hp.

You will gain neither of those (cleaner/safer), so you're wasting your money.
FloydR - drives BMWs that *do* require and perform better on premium.
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wrote

I agree it won't run any better. Why would it run worse?
SNIP a bunch of stuff

Shell is making a big deal about its new premium formulation. Whether or not its any better than anybody elses, who knows?

Floyd, I suspect many of the posters on this board drive BMW's.
R / John
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Yikes; it was late, thought it was a different bbd.
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wrote

Using 91 allows the engine to be build with a higher compression. If you run a lower compression engine, the air/fuel does not compress enough to take advantage of its resistance to combustion. The fuel doesn't burn completely, since it was not ignited in the environment it was designed to ignite in.. so the excess fuel is then burned in the cats... do this for a prolonged period, and you can burn out the cats.
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wrote

Sounds like an urban legend to me. Higher octane isn't combustion resistance, it's resistance to combustion due to compression. Flame front propagation after ignition by spark is identical in both fuels ... they both burn to the same level of completeness.
R / John
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John Carrier wrote:

No, you are dead wrong. Higher octane does translate into (marginally) slower burning. Not just detonation resistance. Whether it is enough to allow raw fuel to escape the combustion chamber is dependant on the engine timing (late ignition and early exhaust valve)
-Fred W
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