what octane for a rotary?
02-20-05, 09:45 PM
#5
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Originally Posted by Midwest 7's
just wondering what everybody uses. my stockport 12a and dell seem to like the pricey stuff. 91 octane
I learned to drive in an '81 but had to sell it when I went to college. After the first year there (military school = we were not allowed to have cars the first year), I bought an '84 GS (which I still own). In the last 2 weeks, I bought an '85 GSL-SE (to keep the GS company), so I'm basically on my third first Gen.
The '81 ran SO MUCH better with the high octane fuel that I've never used anything different for my '84 or the '85 (in the limited time I've had the SE). I'm not a racer (or ricer) but I'd certainly recommend the higher octane fuel.
Different people will give you different opinions though....
02-20-05, 09:49 PM
#6
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High octane = resistance to detonation. The higher the octane rating, the less likely detonation is to occur. High octane fuel DOES NOT provide better performance or increased horsepower.
But high powered engines typically need higher octane fuel because detonation is more likely to occur in higher compression and/ or turbocharged/ supercharged engines, with devastating results. 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.
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, unless the engine is overheated--- in which case you have bigger problems. If anything, 87 octane should actually burn cleaner and reduce emissions, since (at least in theory) a more complete combustion will have taken place by the time it is spat out the exhaust ports.
But boosted rotaries absolutely need high-octane beverages. Detonation in these engines will destroy apex seals and if severe enough will actually cave in the faces of the rotors.
But high powered engines typically need higher octane fuel because detonation is more likely to occur in higher compression and/ or turbocharged/ supercharged engines, with devastating results. 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.
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, unless the engine is overheated--- in which case you have bigger problems. If anything, 87 octane should actually burn cleaner and reduce emissions, since (at least in theory) a more complete combustion will have taken place by the time it is spat out the exhaust ports.
But boosted rotaries absolutely need high-octane beverages. Detonation in these engines will destroy apex seals and if severe enough will actually cave in the faces of the rotors.
02-20-05, 09:51 PM
#7
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I've got an old shop manual from 72 that has a whole chapter devoted to the new fangel Mazda Rotary engine. It says that Mazda has run tests with as low as 67 octane fuel (the lowest they could get) and found no problems. Though I'd say under boost you should run the best you can.
Vernon
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02-21-05, 12:49 AM
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Originally Posted by enigma32
Damn, Aviator is smart 
I've run 87 octane in both my first gens...
I tried 91 for a few weeks one time and didn't notice any improvement.
I've run 87 octane in both my first gens...
I tried 91 for a few weeks one time and didn't notice any improvement.
02-21-05, 01:21 AM
#13
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85, it is the regular here, and there is no way I am paying for midgrade without seeing a worth while benefit.
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
02-21-05, 01:32 AM
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Originally Posted by Aviator 902S
High octane = resistance to detonation. The higher the octane rating, the less likely detonation is to occur. High octane fuel DOES NOT provide better performance or increased horsepower.
But high powered engines typically need higher octane fuel because detonation is more likely to occur in higher compression and/ or turbocharged/ supercharged engines, with devastating results. 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.
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, unless the engine is overheated--- in which case you have bigger problems. If anything, 87 octane should actually burn cleaner and reduce emissions, since (at least in theory) a more complete combustion will have taken place by the time it is spat out the exhaust ports.
But boosted rotaries absolutely need high-octane beverages. Detonation in these engines will destroy apex seals and if severe enough will actually cave in the faces of the rotors.
But high powered engines typically need higher octane fuel because detonation is more likely to occur in higher compression and/ or turbocharged/ supercharged engines, with devastating results. 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.
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, unless the engine is overheated--- in which case you have bigger problems. If anything, 87 octane should actually burn cleaner and reduce emissions, since (at least in theory) a more complete combustion will have taken place by the time it is spat out the exhaust ports.
But boosted rotaries absolutely need high-octane beverages. Detonation in these engines will destroy apex seals and if severe enough will actually cave in the faces of the rotors.
02-21-05, 12:06 PM
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02-21-05, 02:18 PM
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Banned. I got OWNED!!!
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.
02-21-05, 02:52 PM
#19
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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
02-21-05, 03:34 PM
#20
Banned. I got OWNED!!!
Originally Posted by 1stgen4life
Nope, it's just regular 85 octane gas.
02-21-05, 04:37 PM
#21
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Alright, lets clear up a few things. I worked for Esso (that's the Candian Exxon brand name)
for two years, so I have a bit of experience in the industry.
Firstly, (for most companies) mid-grade is just a blend of premium and regular fuel.
Second, it's true that N/A rotaries run better on low octane gas, all things being equal.
However, things are not equal, and most premium gas blends have other additives besides the extra octane. Cleaners are lubricants and all kinds of other stuff gets put in to premuim blends so that the oil companies can justify the extra cost.
With a good running well tuned car (rotary or otherwise) you should hardly notice the difference, but if you are noticing a BIG performance jump when switching fuel grades, that's a sign that somthing isn't quite right.
Moisture or gunky build up in the fuel system are far more common than most people realize. Improperly tuned cars, or cars with small vaccum leaks are also comon benifactors of premium fuel.
I reccomend running good quality regular gas (I like Shell, myself), and using my own additives.
In the winter I put gas-line anti-freeze in the tank every 4th fill-up. The rest of the year, about once every other month. This will remove any water that has managed to contaminate your gas.
I also run a bottle of premium synthetic concentrated fuel system cleaner twice a year. This cleans all the fuel system components and removes any build-up.
I also run MMO in every tank. Lubricates and protects the fuel system and engine.
I have also used Lucas fuel addive instead of the MMO, which seems to do about the same, but without the benifit of acting as a backup for the OMP.
-Spencer
for two years, so I have a bit of experience in the industry.
Firstly, (for most companies) mid-grade is just a blend of premium and regular fuel.
Second, it's true that N/A rotaries run better on low octane gas, all things being equal.
However, things are not equal, and most premium gas blends have other additives besides the extra octane. Cleaners are lubricants and all kinds of other stuff gets put in to premuim blends so that the oil companies can justify the extra cost.
With a good running well tuned car (rotary or otherwise) you should hardly notice the difference, but if you are noticing a BIG performance jump when switching fuel grades, that's a sign that somthing isn't quite right.
Moisture or gunky build up in the fuel system are far more common than most people realize. Improperly tuned cars, or cars with small vaccum leaks are also comon benifactors of premium fuel.
I reccomend running good quality regular gas (I like Shell, myself), and using my own additives.
In the winter I put gas-line anti-freeze in the tank every 4th fill-up. The rest of the year, about once every other month. This will remove any water that has managed to contaminate your gas.
I also run a bottle of premium synthetic concentrated fuel system cleaner twice a year. This cleans all the fuel system components and removes any build-up.
I also run MMO in every tank. Lubricates and protects the fuel system and engine.
I have also used Lucas fuel addive instead of the MMO, which seems to do about the same, but without the benifit of acting as a backup for the OMP.
-Spencer
