happyraul

What are the units for the numbers of the different grades of gasoline (89, 91, 92,...etc) I've always assumed it was a percentace of something, since its close to 100, but not above. Also, what does the higher grade do, in terms of extending the life of your car? Is it worth it?

HamiC

From Car Talk (the best -- and funniest -- NPR radio show ever)......


Dear Tom and Ray:

What is the formula on the gas pump all about? (R+M)/2 -- what's the R? What's the M? -- James

Tom: It's all about octane, James. Octane is a hydrocarbon that, when burned in an engine, has a very high resistance to engine knock, or pinging.

Ray: But since it's very expensive, you never actually burn octane in your engine. The gasolines we use contain no octane. The octane rating simply measures how closely a gasoline compares to pure octane in suppressing knock.

Tom: So a fuel rated 93 octane will resist knock and pinging like a mixture that's 93 percent pure octane.

Ray: There are two different methods used to determine the octane rating of a fuel. There's "R," which stands for "research." The research octane number (RON) is determined in a lab with a test engine running at 600 rpm, which represents a low-compression, low-knock situation.

Tom: Then there's "M," for "motor." The motor octane number (MON) uses a test engine, also in a lab, at a higher rpm. That's supposed to represent higher-speed, higher-temperature operation, where knock is more likely.

Ray: Why is the second one called "motor" when it's also, technically, "research"? Done in a lab, too? We have no idea. Why not L+H for "low" and "high"? Or S+F for "slow" and "fast"? Or if it's going to be meaningless, why not S+R for "Siegfried" and "Roy"?

Tom: Anyway, the way they get the number on the pump is by averaging "R" and "M." Or, put mathematically, "(R+M)/2." So, if the RON of a fuel is 93 and the MON is 87, the octane rating you see on the pump is 90.

Ray: And remember, all the octane rating tells you is how much knock protection you get. A higher-than-necessary octane rating doesn't keep your engine cleaner, make the car go any faster, make your engine last longer or keep your hairline from receding. It just costs more. So use only the octane required by your manufacturer to prevent knock, and no more.

shakran

more practical answers

1) Octane under 100. Yeah, for street driving you won't see 100+ octane. Race cars, however, routinely use 100 and higher octane. 100 is also the octane rating for avgas, the most common aviation fuel.

2) Will it hurt your car?
If your car requires regular unleaded (87-88 octane) and you dump 93 in there, yes it will hurt your car. The 93 burns more slowly than 87, resulting in an incomplete burn by the time the exhaust valves open. The unburned fuel is then depositied in the engine as carbon. Eventually, this carbon builds up enough that it stores heat from the burning fuel. THAT causes the next load of fuel to ignite before it's supposed to - it's being ignited by the carbon's heat rather than the spark plug. This is a condition called predetonation, aka ping, and it's very good at tearing up engines very quickly. What's the solution? Higher octane gas. In other words, unless your car is designed for it, the expensive stuff acts like a drug. Your car becomes addicted, and you will eventually not have a choice but to put the expensive stuff in there.

saltfish

Myths about Unleaded Gasoline
This product information was provided to PSP courtesy of 76 Performance Products, Yorba Linda, California
1. Myth: The higher the octane, the slower the burn.
Fact: In many cases, high octane gasoline has faster burning characteristics than low octane gasoline. It is rarely slower.

2. Myth: Too much octane reduces horsepower.
Fact: Trying a higher octane fuel and getting less performance is usually due to introducing additional variables with the different gasoline which can be overcome by re-tuning the engine.

3. Myth: Too much octane will burn up my engine.
Fact: The only time your engine is aware of octane is when it doesn't have enough. Using a higher octane than the engine needs does not hurt or help.

4. Myth: Street gasoline with oxygenates is junk.
Fact: Street gasolines of today, especially in California, are the best performance gasolines next to racing gasoline.

5. Myth: Leaded gasoline makes more horsepower than unleaded.
Fact: Leaded gasoline is legal for "sanctioned off-highway events only and does not allow the engine to make more power unless detonation is present. More power can be made with a street legal oxygenated unleaded gasoline than with leaded gasoline as long as there is no detonation.

6. Myth: Adding nitromethane to gasoline improves power.
Fact: Nitro knocks the octane number down severely, and makes the mixture way too lean. Jeff Smith, formerly of Hot Rod Magazine, tried this a few years back and destroyed an engine before he got the Air/Fuel ratio correct.

7. Myth: Octane number is power.
Fact: Octane number is resistance to detonation. Higher octane will increase power only if detonation is present.

8. Myth: The octane requirement of my engine is always the same.
Fact: Operating conditions like air temperature, barometric pressure, humidity, and coolant temperature have an impact on engine octane requirement.

9. Myth: Detonation and Pre-ignition are the same.
Fact: Detonation can hurt your engine; Pre-ignition will destroy it.

10. Myth: Mixing regular and premium gasolines is not a good idea.
Fact: All gasolines are miscible and no adverse effects will develop when mixing two or more grades. It is not really necessary to mix gasolines since there are three grades of unleaded gasoline at most service stations.

11. Myth: Octane number is simply a ploy by the oil companies to sell more expensive gasoline.
Fact: Approximately 70°/o of the cars on the road in the US are satisfied with 87 octane or lower. The other 30% need a higher octane gasoline. The higher octane gasolines are available for the people that have cars that need these products because of high compression ratio, or high performance in general. Many automobile manufacturers recommend the use of premium grade gasolines in some or all of their engines. (Cadillac, BMW, Corvette, Mercedes Benz, Lincoln, etc.) We make 76 Competition 100 Octane Unleaded Gasoline for people with highperformance cars that want a higher octane gasoline than what is normally available at the pump.

12. Myth: Gasoline is the same all year in all parts of the US.
Fact: Gasoline is "seasonally adjusted" based on the temperature that is anticipated in that particular marketing area. Changes are made at least six times per year in all areas of the US except Hawaii. A "seasonal adjustment" means that the gasoline is
blended to vaporize more readily in the winter than in the summer. This feature allows cold starts without stalls, and good driveability (no hesitations, stumbles, etc.) while the engine is warming up.

13. Myth: My owner's manual says to use premium grade gasoline, but I use 87 octane and don't hear any ping.
Fact: Many engines that have premium fuel recommendations also have knock sensors. The knock sensor knows when the engine pings and retards the spark timing until ping is gone. This all takes place at a sound level below what the human ear can detect, so the knock sensor may be saving your engine even though you don't know it. The retarded timing will reduce horsepower and fuel economy, so it is best to stay with the car manufacturer recommendation for gasoline octane.

14. Myth: I buy premium grade gasoline because it has more and better additives to keep my injectors and valves clean.
Fact: All gasolines sold in the US are required by law to contain an additive that will keep injectors and valves clean. Tests are required and the additive must be licensed with EPA before it can be used. Most companies use the same amount of additive in all grades of their gasoline.

For your nearest 76 Racing Gasoline Distributor: 1-800-345-0076

Wusz 1/8/02



Good Read

-SF

shakran

#1: Wrong. If it's resistant to burning, then it takes longer in the cylinder before conditions are right to burn it. Therefore, it's slower to burn.

#3: Tear down an 87 engine that someone's been running on 93 for 3 years some time and see what you find

saltfish

http://www.mustangandfords.com/techarticles/30643/

Octane is the most important issue when it comes to selecting the proper gasoline. Octane is a numerical rating that indicates a fuel’s resistance to detonation. The higher the octane number, the more resistant it is to detonation. Higher octane allows an engine-builder to create higher cylinder pressures to make more power. If your engine does not detonate, rattle, or ping on 87-octane fuel, there is no advantage to using a higher-octane fuel. Also, a common fallacy is that higher-octane gasoline burns faster or slower. As octane increases, the components that increase the octane chemically react in the combustion process to merely prevent detonation rather than change the burn rate.


-SF

shakran

I'm not talking about the burn RATE. I'm talking about the amount of time it takes in the engine for the fuel to burn. Once it starts buring, it goes at about the same speed. But it takes longer - i.e. it is slower - to get to the point where it burns. It's slower to burn. If it wasn't then it wouldn't be any different from lower octane gas