There are a number of EXTREMEMLY common misconceptions pertaining to Octane rating, and its effect on your cars performance.
*DISCLAIMER* There is a little bit of chemistry coming at you
On the forums, we frequently see the following questions:
1) When should I use a higher octane fuel?
2) Will a higher octane rating mean better performance?
3) Are fuel additives just as good?
First things first, what is an octane rating?
Its simple. The octane rating translates to the ratio of iso-Octane to Heptane in the gasoline.
Lost you yet?
Its easy.
Here is some very basic organic chemistry:
Here is a lone Carbon molecule
Now a molecule wants to have 8 electrons in its outer shell to be happy. Carbon in its natural state has 4.
So a lone Carbon essentially has 4 empty spaces around it, and it wants to fill them, and the easiest way to do this is with Hydrogen molecules.
So the lone Carbon molecule from before really looks like this:
So we write this as CH4, or METHANE.
Now if we replace one of the hydrogens with another carbon, we are going to make a 2 carbon chain. So, after we fill the empty spaces with hydrogens, we are going to get this:
This can go on and on and on, but for our purposes, we will stop at a 9 Carbon chain. Here is a nice easy table:
1 Carbon: Methane
2 Carbon: Ethane
3 Carbon: Propane
4 Carbon: Butane
5 Carbon: Pentane
6 Carbon: Hexane
7 Carbon: Heptane
8 Carbon: Octane
9 Carbon: Nonane
So we are concerned with iso-Octane and Heptane right?
But where does the word "iso" come from?
Well we can have Octane (8 carbons) like this:
CH3CH2CH2CH2CH2CH2CH2CH3
Or we can rearrange it a bit:
iso-ocatane
CH3C(CH3)2CH2CHCH3CH3
Now for heptane:
CH3CH2CH2CH2CH2CH2CH3
So why do we care about all of this?
Since the octane rating is the ratio of iso-Octane:Heptane, there has to be a difference between the two. Right?
Here it is in a nutshell:
It takes significantly more energy to ignite this iso-Octane than it does heptane.
There are a few reasons for this, more carbons in the chain, increased intermolecular forces, etc., but we dont care about that at the moment. All you need to know is that it takes a lot more energy to ignite iso-octane, so if you have more iso-octane in your fuel......
It is going to take consdierably more energy to ignite that fuel.
Make sense?
Here is an example:
So, if your fuel is 93% Iso-Octane, 7% Heptane, then you will have an octane rating of 93. Which takes more energy to ignite than say 89 octane fuel, which is only 89% iso-Octane.
The ratings are on a 100pt scale, and any ratings higher than 100 are achieved through additives which further delay ignition, making the fuel burn slower, taking more energy to ignite (the fuel ignites at a higher temperature).
So when do you need a higher octane fuel?
When why would you need a slower burning, harder to ignite fuel?
When the pressure/temperature in the combustion is so high that the lower octane fuel will ignite before the end of the compression stroke, starting the power stroke early. If this is confusing, you might want to brush up on
4 Stroke Engines
Now, stock Honda engines were designed with one type of fuel in mind, and using anything other than that type of fuel will cause serious problems.
This is precisely why you cannot simply go out and buy 110 octane for your bone stock LS, and expect it to be faster. In fact, your car is probably going to run like crap.
So what makes the pressure/temperature increase the the point that you would need to use higher octane gas?
Simple, if you significantly change the compression of your motor, or introduce boost (which I highly recommend that you do [
] )
However, if you do either one of those two things, you absolutely HAVE TO TUNE YOUR CAR!!!!!
So when you bring your car in to be tuned, make sure you discuss with your tuner what fuel will be best to run with your setup.
Here are some Organic Chemistry terms that can help you understand the next part:
Aromatic: Compounds containing a benzene ring
Benzene Ring: 6 Carbons in a ring with alternating double bonds
Toluene: A Benzene ring with a methyl sub
Now here is a bit on additives from SniperX:
Toluene as an additive in your gasoline
As Danny50 already mentioned the chemical composition of gasoline, Ill skip that and talk more about octane ratings and why adding toluene to your gas can increase your octane rating. Now, toluene is a natural byproduct of manufacturing gasoline from crude oil, so adding It to your gas tank wont have any adverse effects. I even emailed the original person that I got a lot of info from.
I wrote
Read the article you posted 5 or more years ago about toluene, i was wondering, after all these years, have you had any adverse effects anywhere in any of your cars?
His answer was
Nope. About the only thing that's changed is price :-(
- Charlie
It went from $5 a gallon to $15 a gallon.
From that article:
Q: Will toluene damage my engine or other parts of my car?
A: A 5 or 10% increase in the aromatic content of gas will most likely be well within the refining specifications of gasoline defined by ASTM D4814, which specify an aromatic content of between 20% and 45%. What this means is that if the 92 octane gas that you started off with had an aromatic content of say 30% and you increased it by 10% to 40% you would still be left with a mix that meets the industry definition of gasoline. So the above question would amount to: "Will gasoline damage my engine or other parts of my car?"
Even in the unlikely event that the 92 octane gas has a aromatic content of 45% the resulting mix would still be within the bounds of gasoline sold in other countries.
Mindful of the evil reputation of octane boosters in general, toluene is a very safe choice because it is one of the main octane boosters used by oil companies in producing ordinary gasoline of all grades. Thus if toluene is indeed harmful to your engine as feared, your engine would have disintegrated long, long ago since ordinary pump gasoline can contain as much as 50% aromatic hydrocarbons.
Toluene is a pure hydrocarbon (C7H8). i.e. it contains only hydrogen and carbon atoms. It belongs to a particular category of hydrocarbons called aromatic hydrocarbons. Complete combustion of toluene yields CO2 and H2O. This fact ensures that the entire emission control system such as the catalyst and oxygen sensor of your car is unaffected. There are no metallic compounds (lead, magnesium etc), no nitro compounds and no oxygen atoms in toluene. It is made up of exactly the same ingredients as ordinary gasoline. In fact it is one of the main ingredients of gasoline.
Toluene has a RON octane rating of 121 and a MON rating of 107, leading to a (R+M)/2 rating of 114. (R+M)/2 is how ordinary fuels are rated in the US. Note that toluene has a sensitivity rating of 121-107=14. This compares favorably with alcohols which have sensitivities in the 20-30 range. The more sensitive a fuel is the more its performance degrades under load. Toluene's low sensitivity means that it is an excellent fuel for a heavily loaded engine.
Toluene is denser than ordinary gasoline (0.87 g/mL vs. 0.72-0.74) and contains more energy per unit volume. Thus combustion of toluene leads to more energy being liberated and thus more power generated. This is in contrast to oxygenated octane boosters like ethanol or MTBE which contain less energy per unit volume compared to gasoline. The higher heating value of toluene also means that the exhaust gases contain more kinetic energy, which in turn means that there is more energy to drive turbocharger vanes. In practical terms this is experienced as a faster onset of turbo boost.
Chevron's published composition of 100 octane aviation fuel shows that toluene comprises up to 14% alone and is the predominant aromatic hydrocarbon. Unfortunately composition specifications for automotive gasoline is harder to pin down due to constantly changing requirements.
Now when I looked at the MSDS(Material Safety Data Sheet) for Sunoco
I found that the 260 GTX has 35-45% Toluene and 50-60% Alkylate and that has a octane rating of 98 (R+M)/2. Thats a race fuel
I also found that 260GT with ethanol has 30-40% Toluene and 80-85% Alkalyte. The Toluene rating dropped 5% because the Ethanol added was 5%, so less Toluene was needed. That is a street legal octane rating of 100 (R+M)/2. And thats a street legal fuel.
I have the quotation because if its in a tank, its not guaranteed 100 octane.* see quotation at the bottom of the article
How does this relate and why not add Alkylate and not toluene to our fuel if it makes the octane rating go up more than Toluene?
An Alkylate is a byproduct of alkylation, which is used to make gasoline from crude oil.
Alkylate is a high-octane, branched hydrocarbon mostly made of isooctane and isopentane. Isooctane has a octane rating of 100 (R+M)/2
So, because you cant actually buy alkylate, we cant add it.
However, you can buy toluene, and as mentioned earlier, it has a octane rating of 114 (R+M)/2, which is higher than isooctane. Toluene occurs naturally at low levels in crude oil, but is separated into pure form after the processing of crude oil. Its sold under the name Toluol.
The toluene content is controlled by OSHA, but the alkylate content is controlled by Sunoco, so they can add as much as they please, but cant add as much toluene. Because toluene is a byproduct of alkylation, and is readily available, we can add that to our gas and save ourselves some money while getting a higher octane rating.
How do we know how much to add to our gas tank for a desired octane rating?
The formula is as follows:
(whatever octane you normally use)*(gallons of it) + (114)*(gallons of it) / Tank capacity = New octane rating
In our case we have a 13.2 gallon gas tank. Say youve got a GSR with 12:1 CR and TODA VTEC killer cams, ITBs , et cetera ,et cetera. And your tuner said you need 100 octane. Now, you can go buy it (if you can find it) for 8-10 bucks a gallon or make it using 9.2 gallons of 93 octane and 4 gal of toluene.
Using the formula: (93*9)+(114*4.2)/13.2 = 99.68 (R+M)/2
13 gallons of 100 octane is $104 @ $8/gal
13 gallons of 100 octane is $130 @ $10/gal
9 gallons of 93 octane @ $3/gal is $27
4 gallons of toluene at $15/gal is $60
Total is $87
$87 or $104/$130? Which is better for you to get the same octane rating?
By same I mean this:
You don't know for sure if you are really getting what is being advertised. You should find out if the fuel inspectors verify the actual octane of the racing gasoline in addition to ordinary gasoline. If you paid $3/gallon and only got 94 or 95 octane instead of 100 octane you may conclude erroneously that your car does not benefit from octane boosting.
You don't know what octane boosters are used in the racing gasoline. The worst case scenario is buying leaded racing gasoline without knowing it. Unleaded racing gasoline may still contain damaging octane boosters like MMT or methanol. A very high alcohol content will lead to fuel line erosion, accelerated fuel pump wear, very poor fuel economy and possibly lower performance, as alcohols have a less impressive MON rating than aromatics.
It takes smaller quantities of toluene to achieve the same octane boost compared to 100 octane racing gas. I have not seen unleaded racing gas for sale that exceeds the octane rating of toluene.
Since toluene is not officially sold as a fuel, gas taxes do not apply. Also racing gasoline tend to have higher markups being of interest to the performance minded enthusiast and thus is very likely to be more expensive to buy and use long term than toluene, which is typically used in more mundane applications like paint thinner.
Source:
http://www.team-integra.net/sections/art...cleID=1260