The Mustang Forum for Track Enthusiasts

Track Mustangs Online was built specifically for those who track their Mustangs!

Register Log in

Octane arguments

blacksheep-1

TMO Addict
Messages
2,051
Reaction score
1,452
oh..yeahhh Octane rating..
here's an explanation..sort of


Octane Measurement Methods

Research Octane Number (RON)
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 with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and nheptane.
Motor Octane Number (MON)
There is another type of octane rating, called Motor Octane Number (MON), or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load as it is done at 900 rpm instead of the 600 rpm of the RON. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a 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 gasoline will be about 8 to 10 points lower than the RON. Normally, fuel specifications require both a minimum RON and a minimum MON.
Anti-Knock Index (AKI)
In most countries, including all of those of Australia and Europe the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI). It may also sometimes be called the Road Octane Number (RON), Pump Octane Number (PON), or (R+M)/2.
Difference between RON and AKI
Because of the 8 to 10 point difference noted above, the octane rating shown in the United States is 4 to 5 points lower than the rating shown elsewhere in the world for the same fuel. See the table in the following section for a comparison.


COPYRIGHT 2010 - BONZÍ SPORTS, INC. | BONZISPORTS.COM | TECHSUPPORT@BONZISPORTS.COM




Here's how you can fake the octane rating, generally the octane rating is a resistance to knocking, you can do this in a couple of ways, one is to actually have quality fuel, the other..with regards to resistance to knock, is to add a way to prevent knocking..these days that's ethanol. The ethanol will prevent knock but it does so at the expense of creating more power for the engine. as an example, sprint cars run ethanol or methanol, but they run monster compression, and very small radiators because they don't need as much cooling, in this way they take advantage of what ethanol has to offer. so these additives really do nothing to add power to your engine, but they technically have a higher octane number because they have resistance to knock. This is why an engine that has a potential higher octane rating can make less power, depending on how the octane number is determined.







514gasoline.gif

What is Gasoline?

Gasoline is a complex mixture of over 500 hydrocarbons that may have between 5 to 12 carbons. Smaller amounts of alkane cyclic and aromatic compounds are present. Virtually no alkenes or alkynes are present in gasoline. Compounds in Gasoline.
Gasoline is most often produced by the fractional distillation of crude oil. The crude oil is separated into fractions according to different boiling points of hydrocarbons of varying chain lengths. This fractional distillation process yields approximately 25% of straight-run gasoline from each barrel of crude oil. See Distillation Oil Refining.

The yield of gasoline may be doubled by converting higher or lower boiling point fractions into hydrocarbons in the gasoline range. See Conversion Refining.





Typical Composition of Gasoline

General Name

Examples

Percentage
Aliphatic - straight chain
heptane

30-50
Aliphatic - branched
isooctane
Aliphatic - cyclic
cyclopentane

20-30
Aromatic
ethyl benzene

20-30





What is the octane number?


Fuel octane requirements for gasoline engines vary with the compression ratio of the engine. Engine compression ratio is the relative volume of a cylinder from the bottom most position of the piston's stroke to the top most position of the piston's stroke. The higher an engine's compression ratio, the greater the amount of heat generated in the cylinder during the compression stroke.

If fuel octane is too low for a given compression ratio, the fuel prematurely and spontaneously ignites too early and the fuel charge EXPLODES rather than BURNS resulting in incomplete combustion. The net effect is a loss in power, possible engine damage, and an audible "knock" or "ping", referred to as detonation.
The octane number of gasoline is a measure of its resistance to knock. The octane number is determined by comparing the characteristics of a gasoline to isooctane (2,2,4-trimethylpentane) and heptane. Isooctane is assigned an octane number of 100. It is a highly branched compound that burns smoothly, with little knock. On the other hand, heptane, a straight chain, unbranched molecule is given an octane rating of zero because of its bad knocking properties.

Straight-run gasoline (directly from the refinery distillation column) has an octane number of about 70. In other words, straight-run gasoline has the same knocking properties as a mixture of 70% isooctane and 30% heptane. Many of these compounds are straight chain alkanes. Cracking, isomerization, and other refining processes can be used to increase the octane rating of gasoline to about 90. Anti-knock agents may be added to further increase the octane rating.
Octane rating versus type of compound:

Octane ratings decrease with increasing carbon chain length.
Octane ratings increase with carbon chain branching.
Octane ratings increase in aromatics with same number of carbons.
What octane gasoline should you purchase?

For most automobiles, use the lowest grade of 87 octane, unless they specifically say to use a higher octane gasoline. Using higher octane grades does not provide any extra power or extra mileage.

Note the last paragraph of the article
 
Last edited:

Fabman

Project: "Frankenstang"
Messages
2,612
Reaction score
1,550
Location
Pleasanton: 1/2 way between Sonoma and Laguna Seca
So happy to be on e85.
Only 3 bucks a gallon, more Timing/HP and a cooler running engine.
Unfortunately it not legal for many classes of racing and not always practical for a street application, but it sure is awesome when you can use it. SCCA has cleared it for 2 classes and I believe NASA is ok with it.
Drag racers and circle track guys use it as I'm sure many other sanctioning bodies do.
 

Tonymustang302

TMO Intermediate
Messages
87
Reaction score
38
Location
Chicago, IL
So happy to be on e85.
Only 3 bucks a gallon, more Timing/HP and a cooler running engine.
Unfortunately it not legal for many classes of racing and not always practical for a street application, but it sure is awesome when you can use it. SCCA has cleared it for 2 classes and I believe NASA is ok with it.
Drag racers and circle track guys use it as I'm sure many other sanctioning bodies do.
its $1.40 by me right now lol
 

captdistraction

I am the breaker of things
Messages
1,535
Reaction score
1,025
Location
Phoenix, Az
I won't put less than 100UL in my car, but that's an all out racecar racing in the southwest. If 93 was available, I'd likely blend fuels. I'm tuned for 91, but despite the crazy costs of fuel at 100UL, its cheaper than engines. E85 would be a consideration if I was running a larger tank since I need to be able to make up to 45 minutes at a time.
 

jmv

TMO Beginner
Messages
4
Reaction score
2
The newer cars with 12:1 compression need high octane. And here in cali 91 oct is too low for track usage. On top of performance( my 96oct tune gain 25whp)
Better timing and knock will benefit.
100oct is A piece of mind that i do mind To use:)
I met you at a Vacaville Texaco station last year. Tanker driver and Boss 302 owner. Remember ?
 

Fabman

Project: "Frankenstang"
Messages
2,612
Reaction score
1,550
Location
Pleasanton: 1/2 way between Sonoma and Laguna Seca
I won't put less than 100UL in my car, but that's an all out racecar racing in the southwest. If 93 was available, I'd likely blend fuels. I'm tuned for 91, but despite the crazy costs of fuel at 100UL, its cheaper than engines. E85 would be a consideration if I was running a larger tank since I need to be able to make up to 45 minutes at a time.
Fuel consumption is an issue, its about 20% more. I just went with a 22 gal cell and it is way more than enough.
I'd rather have the extra capacity and not need it then need it and not have it.
 

ARMORINE

TMO Beginner
Messages
8
Reaction score
5
Location
tulsa
Fuel consumption is an issue, its about 20% more. I just went with a 22 gal cell and it is way more than enough.
I'd rather have the extra capacity and not need it then need it and not have it.
what tank did you go with? ive considered going to larger tank but im not sold on it yet.

my current motor mandates E85 with its compression. running 11.7:1 could prolly get away with 93 but its hard to find here in Oklahoma.
 

Fabman

Project: "Frankenstang"
Messages
2,612
Reaction score
1,550
Location
Pleasanton: 1/2 way between Sonoma and Laguna Seca
what tank did you go with? ive considered going to larger tank but im not sold on it yet.

my current motor mandates E85 with its compression. running 11.7:1 could prolly get away with 93 but its hard to find here in Oklahoma.
I used a 22 gal ATL fuel cell and an external pump.
There is some fabrication involved, but it's really not that big of a thing.
I have the whole install in pictures if you are interested. I don't want to trash up the thread too much here.

41412364_10156669873943535_537854579769868288_n.jpg
 

TMO Supporting Vendors

Top