what octane for a rotary?
Absolute Power is Awesome
Joined: Mar 2001
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From: Issaquah, WA
Originally Posted by Aviator 902S
What happens is that the higher-octane fuel burns slower, with a more uniform flame front than lower-octane fuel. This reduces the possibility of an uncontrolled "explosion" in the combustion chamber that is known as detonation. 94 octane is actually less volatile than 87 octane.
Originally Posted by Aviator 902S
Engines with less than a 10:1 compression ratio and no boost can operate just fine on 87 octane fuel. Your normally-aspirated rotary has a 9.2 to 9.4:1 compression ratio and will not detonate with 87 octane,.
My S5 SP engine seems perfectly happy with 87.
Last edited by purple82; Feb 21, 2005 at 10:16 PM.
Adolf Hitler Verfechter
Joined: Sep 2002
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From: Northern South Africa
I`am running 91 Octane unleaded.Its the lowest octane we have here,and i use unleaded to prolong the life of my Lambda sensor.
Would have liked some good old Mobil 87 octane!
Would have liked some good old Mobil 87 octane!
add to cart
Joined: Jun 2002
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From: Saskatoon, SK & Montreal, PQ
87 in my SE not only works fine, there is no noticeable gain with higher octane fuels that would justify the higher price. If I ever went higher-compression (boosted, or RENESIS 
) then - and only then - would I go to a higher octane.
) then - and only then - would I go to a higher octane.
Rotary Freak
Joined: Mar 2003
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From: Calgary, Alberta, Canada
Originally Posted by purple82
I've noticed this is a common misconception. Depending on formulation, higher octane fuel may or may not "burn faster" than lower octane. The only thing octane tells you is the amount of energy required to start the burn, not the energy contained in the fuel or how quickly it will react with oxygen (defining the flame speed).
Octane requirements are as much a part of the combustion chamber design as the compression ratio.
My S5 SP engine seems perfectly happy with 87.
Octane requirements are as much a part of the combustion chamber design as the compression ratio.
My S5 SP engine seems perfectly happy with 87.
Savanna Rx-7
Joined: Jun 2004
Posts: 1,577
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From: yokosuka japan
same here in Japan
Originally Posted by mortenf
Damn...! 87? Over here in Europe, the lowest you can get is 95! And you can still get 98 leaded! We pay about 1,5$ per litre, thats about 6 bucks a gallon!
Lowest off of the base is 95 and costs 120 yen per liter ($1.20) for about 5 bucks a gallon, on the base I have no clue, as they get to much water in their leaky *** tanks = I don't buy there...
Kenn
spoon!
Joined: Sep 2002
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From: Dousman, WI
Originally Posted by christaylor
It's not so much about Octane as heat content. IMSA cars used to run Kerosene. I'd run it too, but Kerosene on a dialetric test is like inhaling a pound of crack before a drug test.
HEAVY METAL THUNDER
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From: Elsenborn, Belgian Eifel
Originally Posted by mortenf
Damn...! 87? Over here in Europe, the lowest you can get is 95! And you can still get 98 leaded! We pay about 1,5$ per litre, thats about 6 bucks a gallon!
Almost true... In Denmark and Germany I saw 91, but not in Belgium. BTW, it's not leaded 98, but 98 with lead replacement (at least in most EU countries) as leaded is forbidden. But you're basicly right, fuel is WAY more expensive overhere, and higher octan rated (95,98, and 99+ in Belgium) European fuel is also better quality though.
Rotary Enthusiast
Joined: Jul 2002
Posts: 1,119
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From: Virginia
When comparing octane ratings it is important to specify which method is used. In North America is is common to use an approximation of Road Octane Number, the average of Research Octane Number and Motor Octane Number. (RON + MON) / 2. Since RON is higher than MON, the same fuel in Europe will have a higher rating when sold based on RON. AFAIK, the quality is the same, at least for the major producers.
Whack 'em and stack 'em
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From: Clarksburg/Bridgeport WV- North Central Appalachia
Originally Posted by purple82
I've noticed this is a common misconception. Depending on formulation, higher octane fuel may or may not "burn faster" than lower octane. The only thing octane tells you is the amount of energy required to start the burn, not the energy contained in the fuel or how quickly it will react with oxygen (defining the flame speed).
Octane requirements are as much a part of the combustion chamber design as the compression ratio.
My S5 SP engine seems perfectly happy with 87.
Octane requirements are as much a part of the combustion chamber design as the compression ratio.
My S5 SP engine seems perfectly happy with 87.
Here is a a damn good explanation and history behind the often misunderstood octane ratings-
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.
The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.
The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.
It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.
During WWI, it was discovered that you can add a chemical called tetraethyl lead to gasoline and significantly improve its octane rating. Cheaper grades of gasoline could be made usable by adding this chemical. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:
Lead clogs a catalytic converter and renders it inoperable within minutes.
The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).
When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline, and octane ratings of 115 are commonly used in super-high-performance piston airplane engines (jet engines burn kerosene, by the way).
The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.
The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.
It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.
During WWI, it was discovered that you can add a chemical called tetraethyl lead to gasoline and significantly improve its octane rating. Cheaper grades of gasoline could be made usable by adding this chemical. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:
Lead clogs a catalytic converter and renders it inoperable within minutes.
The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).
When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline, and octane ratings of 115 are commonly used in super-high-performance piston airplane engines (jet engines burn kerosene, by the way).
Absolute Power is Awesome
Joined: Mar 2001
Posts: 1,973
Likes: 5
From: Issaquah, WA
Originally Posted by Tom
If you mean 'energy' in the form of compression then yes. But that's all octane indicates. Not burn rates, atomization with oxygen or any of that other stuff. 87 will explode just as fast as 92.
Here is a a damn good explanation and history behind the often misunderstood octane ratings-
[b]
Here is a a damn good explanation and history behind the often misunderstood octane ratings-
[b]
Whack 'em and stack 'em
Joined: Mar 2003
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From: Clarksburg/Bridgeport WV- North Central Appalachia
^ Yes- that is in essence what I was referring to. Differentiating between the activation energy via 'spark' and 'compression', which are two different things (and achieving the AE trigger via compression is a bad thing in a motor)
It is funny how gas companies can use descriptive words like 'Supreme' and 'High Test' with higher octane fuels.. Sooo damn misleading.
I used to love hearing people say they were gonna run 'jet fuel' in their muscle cars.. I was like "Oh yeah? I've got a 'jet fuel' powered tractor back at our farm in Ohio!" They were like "ooooohhh"
It is funny how gas companies can use descriptive words like 'Supreme' and 'High Test' with higher octane fuels.. Sooo damn misleading.
I used to love hearing people say they were gonna run 'jet fuel' in their muscle cars.. I was like "Oh yeah? I've got a 'jet fuel' powered tractor back at our farm in Ohio!" They were like "ooooohhh"
Rotary Freak
Joined: Mar 2003
Posts: 1,711
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From: Calgary, Alberta, Canada
Originally Posted by Tom
^ Yes- that is in essence what I was referring to. Differentiating between the activation energy via 'spark' and 'compression', which are two different things (and achieving the AE trigger via compression is a bad thing in a motor)
It is funny how gas companies can use descriptive words like 'Supreme' and 'High Test' with higher octane fuels.. Sooo damn misleading.
I used to love hearing people say they were gonna run 'jet fuel' in their muscle cars.. I was like "Oh yeah? I've got a 'jet fuel' powered tractor back at our farm in Ohio!" They were like "ooooohhh"
It is funny how gas companies can use descriptive words like 'Supreme' and 'High Test' with higher octane fuels.. Sooo damn misleading.
I used to love hearing people say they were gonna run 'jet fuel' in their muscle cars.. I was like "Oh yeah? I've got a 'jet fuel' powered tractor back at our farm in Ohio!" They were like "ooooohhh"
So kerosene-based fuels are excellent when burned under extreme high pressure, as in deisels or turbines. But muscle cars with compression ratios on the order of 11: 1 just won't get it done.
Last edited by Aviator 902S; Feb 23, 2005 at 02:57 PM.
Joined: Mar 2003
Posts: 1,270
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From: up to my ass in alligators
Originally Posted by brak
Are you talkin E-85? We have to run that in all our Gov't vehicles.
85% Ethanol (alcohol)
15% unleaded (so people don't drink it)
I wish i could set the Rex to run it. you have to have a special cam, but it really makes a noticable difference in power and fuel economy. Filled the govie with 90 on accident, boy did it run like crap compared to the E-85
Oh yeah, I run 87 in the FB
85% Ethanol (alcohol)
15% unleaded (so people don't drink it)
I wish i could set the Rex to run it. you have to have a special cam, but it really makes a noticable difference in power and fuel economy. Filled the govie with 90 on accident, boy did it run like crap compared to the E-85
Oh yeah, I run 87 in the FB
Also, e85 doesn't make a car run any better than unleaded gasoline, it burns faster and therefore you can't go as far on a tank of it. It also leads to far more driveability problems like poor idle when cold or on hot starts. Put all those things together and the only people benefitting from e85 are the corn farmers
Lean Mean Speed Thingie
Joined: Mar 2002
Posts: 1,102
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From: Moscow, ID
Originally Posted by brak
I wish i could set the Rex to run it. you have to have a special cam
. I'm really suprised i was the first one to jump his **** on this! All you smartasses are slacking!
EliteHardcoreCannuckSquad
Joined: May 2001
Posts: 4,126
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From: Acton, Ontario, Canada
Originally Posted by Mills
the only people benefitting from e85 are the corn farmers
It's a much better long term choice as sooner or later we WILL run out of fossil fuels, and E85 can help string our supply along A LOT longer....
Full Member
Joined: Jul 2002
Posts: 177
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From: Perth, Western Australia
can someone explain how if i fill my car with 89 octane im lucky to see 220km's per tank, but if i fill it with 98 i get about 260km's a tank??? i dont drive it any differently, just cruise to work and back
and it feels like it pulls harder too, yet everything you guys say should mean that it doesnt???
im all confused
-James
and it feels like it pulls harder too, yet everything you guys say should mean that it doesnt???
im all confused
-James
Joined: Dec 1999
Posts: 7,855
Likes: 517
From: Behind a workbench, repairing FC Electronics.
Back when I was a computer tech, and I had first gotten my 7, one of the older techs looked at it and said, "Woah man. One of those Mazdas with the Rotary Engine eh?"
So I said yeah...
He goes into a story (like many others who see it or hear about it do...) about how he had a rotary back in the day... So he starts telling me about his RX-3 Wagon...
He used to hang out with a buddy of his that lived near an airport, and who worked night security or something there... He's go by an dhave some beers or play cards late at night to keep the guy company, because it was uneventful... One night, he goes with a very low tank of gas, and upon leaving, the car wouldn't start because it was totally drained.
He asks the airport guy if there was any gasoline around. The guy says the only thing they have is this "Blue fuel" for the airplanes.
So they push the wagon over to the refueling tank and funnel some into the wagon... The older tech told me, "Man, that thing never ran better." He never was able to get the same effect out of pump gas.
So I said yeah...
He goes into a story (like many others who see it or hear about it do...) about how he had a rotary back in the day... So he starts telling me about his RX-3 Wagon...
He used to hang out with a buddy of his that lived near an airport, and who worked night security or something there... He's go by an dhave some beers or play cards late at night to keep the guy company, because it was uneventful... One night, he goes with a very low tank of gas, and upon leaving, the car wouldn't start because it was totally drained.
He asks the airport guy if there was any gasoline around. The guy says the only thing they have is this "Blue fuel" for the airplanes.
So they push the wagon over to the refueling tank and funnel some into the wagon... The older tech told me, "Man, that thing never ran better." He never was able to get the same effect out of pump gas.
Absolute Power is Awesome
Joined: Mar 2001
Posts: 1,973
Likes: 5
From: Issaquah, WA
Originally Posted by deeman111
can someone explain how if i fill my car with 89 octane im lucky to see 220km's per tank, but if i fill it with 98 i get about 260km's a tank??? i dont drive it any differently, just cruise to work and back
and it feels like it pulls harder too, yet everything you guys say should mean that it doesnt???
im all confused
-James
and it feels like it pulls harder too, yet everything you guys say should mean that it doesnt???
im all confused
-James
Whack 'em and stack 'em
Joined: Mar 2003
Posts: 1,373
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From: Clarksburg/Bridgeport WV- North Central Appalachia
^ and what vehicle is he referring to. If it's a boinger, then I'd ask if he's knocking with lower octane, which very well may cause poor(er) mileage.
If it's the 12A bridgeported rx-7 listed in his profile- then I'd ask- why do you give a rat's ***!
If it's the 12A bridgeported rx-7 listed in his profile- then I'd ask- why do you give a rat's ***!
Rotary Freak
Joined: Mar 2003
Posts: 1,711
Likes: 0
From: Calgary, Alberta, Canada
Originally Posted by Pele
Back when I was a computer tech, and I had first gotten my 7, one of the older techs looked at it and said, "Woah man. One of those Mazdas with the Rotary Engine eh?"
So I said yeah...
He goes into a story (like many others who see it or hear about it do...) about how he had a rotary back in the day... So he starts telling me about his RX-3 Wagon...
He used to hang out with a buddy of his that lived near an airport, and who worked night security or something there... He's go by an dhave some beers or play cards late at night to keep the guy company, because it was uneventful... One night, he goes with a very low tank of gas, and upon leaving, the car wouldn't start because it was totally drained.
He asks the airport guy if there was any gasoline around. The guy says the only thing they have is this "Blue fuel" for the airplanes.
So they push the wagon over to the refueling tank and funnel some into the wagon... The older tech told me, "Man, that thing never ran better." He never was able to get the same effect out of pump gas.
So I said yeah...
He goes into a story (like many others who see it or hear about it do...) about how he had a rotary back in the day... So he starts telling me about his RX-3 Wagon...
He used to hang out with a buddy of his that lived near an airport, and who worked night security or something there... He's go by an dhave some beers or play cards late at night to keep the guy company, because it was uneventful... One night, he goes with a very low tank of gas, and upon leaving, the car wouldn't start because it was totally drained.
He asks the airport guy if there was any gasoline around. The guy says the only thing they have is this "Blue fuel" for the airplanes.
So they push the wagon over to the refueling tank and funnel some into the wagon... The older tech told me, "Man, that thing never ran better." He never was able to get the same effect out of pump gas.
Either way, these fuels had gobs of lead in them, even the "low lead," but especially the 100/130 green stuff. If he ran just one tank (or more likely, just a few gallons to get to the next station) the lubricating qualities of the lead "may" have contributed to performance by reducing friction, if only for a short time. (Or the performance increase "may" have been his imagination, and based on the mistaken assumption that higher octane = more hp).
Any prolonged use of this fuel in engines with as close running clearances as the rotary or modern automotive engines have would clog up seals (and rings in boingers), as well as foul the plugs. He obviously didn't run enough of this fuel through his car to witness the more negative aspects.
Last edited by Aviator 902S; Feb 24, 2005 at 03:55 PM.
Whack 'em and stack 'em
Joined: Mar 2003
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From: Clarksburg/Bridgeport WV- North Central Appalachia
tetraethyl lead was added to 'boost' octane ratings for gasoline.
I would imagine the low(er) lead stuff was for aircraft with low compression ratio or standard piston engines.
I would imagine the low(er) lead stuff was for aircraft with low compression ratio or standard piston engines.