Projected Octane ratings for specific Compression ratios:
Compression ~ Octane Number ~ Brake Thermal Efficiency
5:1 ~~~~~~~~~~ 72 ~~~~~~~~~ -
6:1 ~~~~~~~~~~ 81 ~~~~~~~~~ 25 %
7:1 ~~~~~~~~~~ 87 ~~~~~~~~~ 28 %
8:1 ~~~~~~~~~~ 92 ~~~~~~~~~ 30 %
9:1 ~~~~~~~~~~ 96 ~~~~~~~~~ 32 %
10:1 ~~~~~~~~~ 100 ~~~~~~~~~ 33 %
11:1 ~~~~~~~~~ 104 ~~~~~~~~~ 34 %
12:1 ~~~~~~~~~ 108 ~~~~~~~~~ 35 %
Remember this statement earlier in your reading: Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark, for example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). Octane Mixing Chart
Gallons of 100 Octane Racing Gasoline (Across)
Gallons of 92 Octane Station Gasoline (Down)
~~~~~~1. 2. 3. 4. 5. 6. 7. 8. 9. 10.~~~~~~~~~
1. 96.0 97.3 98.0 98.4 98.7 98.9 99.0 99.1 99.2 99.3
2. 94.7 96.0 96.8 97.3 97.7 98.0 98.2 98.5 98.7 98.8
3. 94.0 95.2 96.0 96.6 97.0 97.3 97.6 97.8 98.0 98.2
4. 93.6 94.7 95.4 96.0 96.4 96.8 97.1 97.3 97.5 97.7
5. 93.3 94.3 95.0 95.6 96.0 96.4 96.7 96.9 97.1 97.3
6. 93.1 94.0 94.7 95.2 95.6 96.0 96.3 96.6 96.8 97.0
7. 93.0 93.8 94.4 94.9 95.3 95.7 96.0 96.3 96.5 96.7
8. 92.9 93.6 94.2 94.7 95.1 95.4 95.7 96.0 96.2 96.4
9. 92.8 93.5 94.0 94.5 94.9 95.2 95.5 95.8 96.0 96.2
10. 92.7 93.3 93.8 94.3 94.7 95.0 95.3 95.6 95.8 96.0
Note: for unleaded engines only, Sunoco 100 and Unocal 100 are the only recommended fuels. Older engines that were produced prior to unleaded fuel or more modern engines heavily modified to handle lead fuel. Then there are several options available to you from various Mfg.'s such as 110, 112, & 116 octane ratings... Also of importance do not be fooled into Avaition Fuel. Yes, it has a high octane rating but is designed to be used at alititude where the air is less dense & colder...
What about those little bottles of Octane Booster sold at Auto parts stores?
Do they work? Sure! The good ones do. First, let's take a look at what a good octane booster will do to your gasoline. Please make note of that word "good," because there is a lot of trash out there on the market...
Octane boosters can be broken into three types based on their active ingredients. Methyl cyclopentadienyl manganese tricarbonyl
(MMT) and
ferosene are used in limited amounts in off-the-shelf boosters. The majority of commercial boosters use
MMT. Another type of booster uses
alcohols or
aromatics as the active ingredient. Many racers use toluene as a home-style octane booster. Toluene, an aromatic circular hydrocarbon chain, is a regular component of pump gas and is available in various grades at chemical supply stores. Premium street gasoline carries roughly 3- to 5% toluene, which partially helps octane characteristics. Unocal's 100-octane race gas has almost 25% toluene.
The drawback to any of these additive ingredients is the diminishing effect they have on higher-octane fuels. Adding the same booster to 87-octane pump gas will yield a lot more octane gain than adding a bottle to 91-octane premium gas. Excessive concentrations of these additives also damage emissions-control hardware, such as spark plugs, injectors, oxygen sensors and catalytic converters. This is why most off-the-shelf boosters have an emissions-legal street formulation and an off-road formulation that exceeds the government-regulated concentration of MMT or ferosene.
WILL OCTANE BOOSTERS ADD HORSEPOWER?
No. This is a misconception. Octane in itself does not add power. However, an engine that's forced to run on fuel with a lower octane than what's needed will run hot, detonate, and eventually lose power. The proper octane level will let the engine run to its full potential, but won't transform it into something special.
SIDE EFFECTS OF OCTANE BOOSTERS
Will attack plastics, rubbers and some fiberglass. Discolor and attack most paints. Foam filters will deteriorate if cleaned in a booster-carrying gasoline. So will the glues holding the filter together. Some oils are affected by octane boosters. Most normal oils are not bothered, but if you have any doubt about your favorite brand, check with the manufacturer, to play it safe. Two-stroke users have to pay particular attention to this. Can make an engine run rich. Rejetting may be necessary. Are toxic to the skin, and the fumes can make you sick. Exposure to air can cause a 50-percent breakdown in effectiveness. Ultraviolet rays - that's plain old sunlight- will make octane boosters deteriorate. Will attack gas tank sealants and could plug up your entire fuel system if used together. Cost a lot of money. NOW...THE GOOD SIDE Don't let all of that scare you. Octane boosters have a real place in the world today. Here are some of the good things they can do: Better throttle response. You can actually feel it. Gets better mileage. Also, you can often lean out the carb slightly when using octane boosters, which will give improved mileage. Best performance possible from your engine, short of using race gas. Reduce detonation and pinging. Clean out deposits. A good booster will actually let the engine run cleaner and inhibit carbon build-up. Acts as a gasoline stabilizer when the machine is left to sit for a period. Gas stores longer with a good octane booster in the fuel. Lets you use whatever gas is available at the time. A good booster doubles as an emulsifier and can keep small amounts of water in suspension. Fuel system condensation is a very real problem, especially when the machine sits for long periods of time between use.
HOW TO TELL A GOOD OCTANE BOOSTER FROM A POOR ONE
The market is loaded with octane additives. Here's one rule of thumb: if the product comes in a clear or transparent bottle, don't even consider it. Ultra violet rays cause deterioration.
There should be specific directions on the label, i.e., how much octane booster to use to how much gas. And, there should be a listing of how many numbers the octane will be raised per ounce of booster used to each gallon of gas. A good octane booster will raise a gallon of gas by two-and-a-half numbers with one ounce added. If the label isn't specific, don't bother with the product.
Consider the cost per ounce. You can get a good octane booster to add 2-1/2 numbers per ounce per gallon for around 30 cents per ounce. Some of the cheaper products might not be as efficient as the more expensive ones.
Make sure the label has a toxicity warning. If it isn't toxic, it isn't going to work. And if it is toxic and there's not a prominent warning, this borders on criminal negligence. Some of the better octane boosters are aniline, nitro benzine and toluene. Additives like acetone and sulfurs can be very corrosive.
Better octane boosters also have metal deactivators in them. This lessens the corrosive action of the additive on brass. And, as you know, all of your jets are made of brass, as are a number of parts in the carb and fuel system. Traces of brass can destroy volatilities in the gas.
Here are a couple of brands that have been tested and passed and can be truly called octane booster... many others out there are a waste of money!
1. (NOS) Racing Formula octane booster
2. Outlaw's Super Concentrated Octane Booster
A good rule of thumb in purchasing an Octane booster is to purchase as fresh a date as possible, it must be in a metal container and have either MMT, alcohols, or aromatics as its active ingredient... a Bottle (12oz) to 15 Gallons of 91 octane fuel is all you should need... This should give you exatly what you need for any engine boosted or not that runs below a 11.1 compression or running boost on turbo/supercharged engines of around 6-8 PSI. If your beyond that compression then Race fuel is your only option... and at last count thats running about $7 a gallon...
Thank you
Hope this has been insightful and the thread is now open for discussions.