Octane question
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sledcrazy,
Many S.A.E. papers have been written on this subject. I will try to summarize. Ocatane by itself has very little to do with BTU or heat content. Octane is a numerical value given to a fuel that relates it to iso-octane. The value makes the relationship of all fuels on the same playing field as iso-octane as far as combustion goes. There are two types of ratings used, one is the research method and one is the motor method. You will see on a pump R+M/2. This is the average of the two. Octane means resistance to burn. In other words the higher the number the harder it is to ignite or higher resistance to auto ignition. As octane number increases the temperature in a controlled engine will decrease because the energy can not be released. The only way to make more power with higher octane comes from raising the compression ratio. Compression ratio has a direct relationship to power output, octane does not. If your engine is designed for 87 octane and you run 93, you are waisting money and power. You waist power because your ignition, compression ratio, and port timing is designed to have the fuel ignite easier. If the fuel does not complete combustion by 15 deg ATDC the process was waisted. Hope this helps.
GLH
Many S.A.E. papers have been written on this subject. I will try to summarize. Ocatane by itself has very little to do with BTU or heat content. Octane is a numerical value given to a fuel that relates it to iso-octane. The value makes the relationship of all fuels on the same playing field as iso-octane as far as combustion goes. There are two types of ratings used, one is the research method and one is the motor method. You will see on a pump R+M/2. This is the average of the two. Octane means resistance to burn. In other words the higher the number the harder it is to ignite or higher resistance to auto ignition. As octane number increases the temperature in a controlled engine will decrease because the energy can not be released. The only way to make more power with higher octane comes from raising the compression ratio. Compression ratio has a direct relationship to power output, octane does not. If your engine is designed for 87 octane and you run 93, you are waisting money and power. You waist power because your ignition, compression ratio, and port timing is designed to have the fuel ignite easier. If the fuel does not complete combustion by 15 deg ATDC the process was waisted. Hope this helps.
GLH
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FUEL IS NOT RATED LIKE JACK DANIELS WHISKEY!
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glhracing,
let me tell you something from my experience then i think it will create a question you can answer for me. i was told by a fuel engineer that high test is best no matter what you use it in because of cleaner whatever from tank to exhaust, i till then always used fuel as bad as what you get from a squeezed oily rag from anybodies pump. i decided to try high test on a 4 day trip and i noticed the sled got much better mileage so i have been using it since. now in this warm season my plugs seem to be wet once in awhile and i think that after reading what you posted i should go back to regular fuel in the warmer weather.
let me tell you something from my experience then i think it will create a question you can answer for me. i was told by a fuel engineer that high test is best no matter what you use it in because of cleaner whatever from tank to exhaust, i till then always used fuel as bad as what you get from a squeezed oily rag from anybodies pump. i decided to try high test on a 4 day trip and i noticed the sled got much better mileage so i have been using it since. now in this warm season my plugs seem to be wet once in awhile and i think that after reading what you posted i should go back to regular fuel in the warmer weather.
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2,083 Posts
Most generally gas companies refine higher octane gas longer (remember the amoco ultimate commercials) and add more detergents so you think you're getting more bang for your buck. My buddy was running premium in his suburban and was having drivability problems. They finnally traced the problem back to him running 93 octane. Apparently it was screwing up the computer which was adjusting everything in the ignition system for 87 octane.
Paul,
I get asked this question ALOT. There is some problem with what I have posted and hope nobody would find it, however you have. As long as the fuel contains the same constituents the previous post holds true. The problem is that each company has their own ingrediant. Detergents, flame increasers, anti-foam, emulsifiers, and so-on. That is why some fuels burn better than others in some situations. Without pulling out one of my college papers and re-writing it, it is best to use the minimum octane required, that is if the gasoline is "fresh" and from a known supplier. The canadian gasoline varies ALOT from the US based fuels as well as from station to station. We tested some 150 different fuels. Some were from the same manufacturer but different state. The difference is mind blowing. Each manufacturer has their own distilation curve, that is what depicts what properties the fuels contain. I can tell you that SUNOCO is a HOTTER fuel than MOBILE, only a few BTU's but... Mobile also has more detergent than CITGO. Does it make it a better fuel?? Not really. Some facts: gasoline has a Sg of .72-.76. Contains about 20,000 btu/lb. The list goes on and on.
GLH
I get asked this question ALOT. There is some problem with what I have posted and hope nobody would find it, however you have. As long as the fuel contains the same constituents the previous post holds true. The problem is that each company has their own ingrediant. Detergents, flame increasers, anti-foam, emulsifiers, and so-on. That is why some fuels burn better than others in some situations. Without pulling out one of my college papers and re-writing it, it is best to use the minimum octane required, that is if the gasoline is "fresh" and from a known supplier. The canadian gasoline varies ALOT from the US based fuels as well as from station to station. We tested some 150 different fuels. Some were from the same manufacturer but different state. The difference is mind blowing. Each manufacturer has their own distilation curve, that is what depicts what properties the fuels contain. I can tell you that SUNOCO is a HOTTER fuel than MOBILE, only a few BTU's but... Mobile also has more detergent than CITGO. Does it make it a better fuel?? Not really. Some facts: gasoline has a Sg of .72-.76. Contains about 20,000 btu/lb. The list goes on and on.
GLH
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2,083 Posts
If it calls for 93 use 93. Obviously it's a higher compression engine.
Just somthing to think about, old gas can be harmfull to a 2 cycle engine right? How many people do you know that are willing to fill up their car on higher priced premium gas? Some but not alot. Now which gas is fresher mid-grade or premium? I never use preimum only mid-grade. Also around my home town alot of premium fuels are ethonyol or non-oxyganated, also a bad move. What do you think? I would like to here some opinions on this!
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556 Posts
this is like chasing your tail. I used to have fuel tested to the tune of $150 per test at pheonix lab. in chicago il. for my race engines. I'll make a long story short, buy the octane recomended for a stocker,and if you have port work and compression upgrades go for the higher octane nuf said.
GLHRACING is dead on.
If your sled is rated for 87 then use 87 for running on the trails. However i would use 91 for strait on lake running.
Lake running is where most problems start and even though your engine is made to run 87. Carbon build up or hot spots on your sparkplugs could pre ignite and cost you a piston.
And to clerify When i say lake racing i dont mean 1/4 mile. I mean darting accross lakes at 3/4 throttle or full.
If your sled is rated for 87 then use 87 for running on the trails. However i would use 91 for strait on lake running.
Lake running is where most problems start and even though your engine is made to run 87. Carbon build up or hot spots on your sparkplugs could pre ignite and cost you a piston.
And to clerify When i say lake racing i dont mean 1/4 mile. I mean darting accross lakes at 3/4 throttle or full.
Here are my 2 cents worth (Canadian). I recently read a similiar question in the Toronto Star about fuel pertaining to Ontario's Drive Clean emission testing. The person who answered the question stated that when you go in for your test that you should use a regular grade gasoline because it burns quicker than premium.
The second comment this person had was that before the test you should fill up with a fuel containing alcohol. The extra oxygen this fuel carries will help your emission results.
DISCLAIMER: I would hope you all realize that you shouldn't run gasahol in your sleds. This fuel without jetting adjustments creates a lean burn and at lower temps can cause the motor to lean out & go bye bye
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The second comment this person had was that before the test you should fill up with a fuel containing alcohol. The extra oxygen this fuel carries will help your emission results.
DISCLAIMER: I would hope you all realize that you shouldn't run gasahol in your sleds. This fuel without jetting adjustments creates a lean burn and at lower temps can cause the motor to lean out & go bye bye
In my area we have the I/M 240 test.They run your car on a dyno and follow a speed trace for 240 seconds if it doesn't pass the quick test.HCs,COs and NOX are measured in grams per mile.Oxygenated,alcohol,reformulated fuels (whatever you want to call it),definetly helps reduce emissions.Just for the record revrnd,high octane can help your vehicle pass if you have a NOX failure.Again high octane cools combustion temps,thus reducing NOX.Most NOX failures come from faulty egr systems,inducing an inert gas lowers combustion temps.Sorry I rambled on but I do this for a living.
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The only reason I don't run 92 octane is because not to many people use this grade in the winter. This results in the gas siting in the ground all winter collecting water. Thus the 87 octane will give you a better run anyways. I have also had frozen carbs because of high grade gas on my old sled. The only place I buy high grade is at the lakes where there is high snowmobile trafic.
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