I want to start this post with an explanation as to why so many things get perceived wrong. More than 17 years ago I was asked to write a paper detailing suspension design, myth & fact! If you ask nearly every car guy who wants a car to handle better than the factory setup & you inquire what they will do to achieve that? They will say nearly to a man, lower the car! This not only is categorically wrong, but the complete opposite! There are a few exceptions where a double wishbone is involved, but that carries a big caveat to do so & Macpherson struts have no exceptions for lowering! Yet to this very day this still dominates the mentality of those looking for a more aggressive handling car. Because those that don’t know or don’t have a clue as to how to accomplish such a task say it’s so! Then the followers who have no clue & looking for the easiest way, buy into it, because they don’t know either & have no interest in finding out the actual fact! Which takes a lot of work & math.

So how this applies to the subject of this post; OCTANE! Do you know what octane is: it’s chemical structure? Do you know how many formulations there are? Do you know how many different octane rating systems there are & why does it matter? 

Recently there was a conversation about dieseling, timing & how one of the components that can cause this is octane. It won’t take you much research to find out how much damage low octane fuel & barreling down the road, you know blow out the carbon, can cause! Especially if you ignore what might be there, but can’t hear it! Can detonation occur without you knowing? Can detonation shorten the life of your engine? 

To these questions there are these answers. Octane is a hydrocarbon with a chemical formula. Its purpose is to resist an engine's ability to knock or pre-ignite. It also has an impact on the power output, AKA energy output, of gasoline. There are 18 different formulations of octane. In short they are all either methylheptane, dimethylhexane, ethylhexane, trimethylheptane or diethylbutane. All of these have different formulations that give the 18 different forms.

There are three different octane rating systems. This is where the separations start to impact fuel quality. There is the RON system. This stands for research octane number. This system is the most used worldwide. Then there is the MON system. This is used by the industry such as petroleum refiners, car manufacturers, engine builders & fuel marketers. Then there is the USA! We use the AKI rating system! This is an average of the RON & the MON! This is actually superior to the RON system, I will explain why in a bit, but this is why it matters! 

I can't wait for Last Indian's next chapter!

I was really shocked when Street Outlaws went down under to race only to find what they called racing fuel wasn't close to the octane we are used to. They had to detune to run the Aussies.

3 hours ago, JUSTA6 said:

I was really shocked when Street Outlaws went down under to race only to find what they called racing fuel wasn't close to the octane we are used to. They had to detune to run the Aussies.

didnt know that !!!!

9 hours ago, 64 kiwi boni said:

didnt know that !!!!

Farmtruck and Azian went to a shop to have NOS tanks filled and had to buy fuel in drums to race the truck.

When you buy a grade of fuel in the same brand in the same country you get more of a % of the octane additive as you go up in grade! That’s it, nothing complex, JustA more! But, what formula it is does make a difference & what system the formula was tested on makes a difference! Hands down the best formula of the 18 formulas is 2,2,4 trimethylhepane. This has been proven through the testing of both the RON & MON.

So let’s take the RON test system. This is the most used worldwide for the consumer at the pump. So Europe, England, Australia, etc, but not the USA. 

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine at 600 rpm with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.[8] The compression ratio is varied during the test to challenge the fuel's anti-knocking tendency, as an increase in the compression ratio will increase the chances of knocking.

But, the MON test system uses a different methodology. The Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 lower than the RON.

What does this really mean? Well, recently there was a post stating the use of a minimum of 95 octane & when possible 98 octane! Yet the misconception, AKA perception, that it was relevant to the USA octane! It is not! Those numbers are of the RON standard. Which places them at a minimum of 6 octane numbers lower than they are when compared to the USA! Meaning they would actually be no more than an 89 & 92 octane, but possibly lower depending on other factors. Those other factors are fuel brand, which means there could be a different octane formula other than the 2,2,4 trimethylheptane. Which can further lower the octane rating. The USA uses the AKI rating for octane! It stands for anti knock index. This rating basically uses the RON & MON combination with a mathematical formula! So in general USA octane rating lie in about the middle of the two. Thus about 6 octane numbers lower than the RON octane numbers!

You didn’t really think that the station down the street that sells the same octane rated gas was giving you the same gas did you? Those brands are using less costly octane formulations, less detergents & in many cases not much else!

Edited 8 hours ago8 hr by Last Indian

Well, I'm a believer, I honestly would've never thought octane could affect an engine the way it did mine. As much time as I spent, as much help as y'all gave me, and not being able to stop the dieseling. I mean y'all seen the videos, I've driven her a number of times since and no dieseling. I even went and put 10 gallons of 87 octane a couple weeks ago to satisfy stupid curiously and when I shut her off, she DID diesel. Dumped in a bottle of booster and justa like before, no dieseling. It's still mind blowing to me.

17 hours ago, JUSTA6 said:

I was really shocked when Street Outlaws went down under to race only to find what they called racing fuel wasn't close to the octane we are used to. They had to detune to run the Aussies

I remember that episode!

Now, here is some unacknowledged & even less understood information by the general population! The octane additive is degraded due to the presence of ethanol in the fuel! Why? Ethanol, no matter what they tell you, is worthless in gasoline! Yes, it actually raises the octane rating of gasoline fuel because ethanol combusts at a high temperature, but & it’s a big but; it has half the BTU content! It takes twice as much ethanol to equal the power output of gas. 

So in plain words, it takes twice as much ethanol to accomplish the same task! Which means when you buy E85, which has 15% ethanol in it you are getting 15% less energy out of the gas. It only gets worse from there. Ethanol is hygroscopic, it attracts water! Then with the presence of water all kinds of bad things happen. In time it causes phase separation & the degradation of trimethylheptane as well as the other octane formulas. Which means whatever octane rated gas you bought, you really aren’t getting! Unless you use it relatively quick. Otherwise it no longer has that octane. So, other than rapid use of the fuel & hopefully no water absorption do you actually get say a 93 octane gas! Look at it this way you buy E85 it takes you a week to go through half a tank. It is hot, high humidity, the fuel has started to absorb moisture. You add back the half tank you used. This continues until little by little the concentration of water suspended in your fuel tank is a breeding ground for phase separation & degradation! Thus lowering your octane rating! So let’s add sta-bil marine formula! You will remove the ethanol from the fuel, but you still lower your octane rating because you removed a component from the fuel that was part of the original octane rating! Do you see how that works? No matter what they have you by the short hairs. Your only real choice is use marine sta-bil to remove the ethanol, then add a portion of octane boost to your fuel to bring it back to the octane you want!