fuel octane ratings - and the effects of...
03-26-2002, 05:52 PM
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fuel octane ratings - and the effects of...
just read this post on a diff forum..can anyone comment on its validity (for truth? ehhe)
by the way...this was posted on an aussie site..so 95 and 98 RON ratings is what we get here - not sure how it compares with US RON ratings...most probably different..as i hear you premium fuel has a RON rating of low 90's
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There's a massive misconception going around about what octane actually means. Octane is actually a measure of a fuels resistance to burning. The higher the octane, the higher the resistance. By that measure you could say water has an octane of several 1000.
In any given engine running at optimal conditions there would be no difference in power running 98 or 95 octane fuel.
The difference comes about outside optimal conditions, such as on a hot day after idling in traffic for 20 minutes. Under these conditions a low octane fuel is more likely to detonate. Your ECU picks this up way before you will hear it and retards ignition. You'll notice it as a loss of power. In these sorts of conditions a higher octane is better.
But if your car runs fine on 96 octane (is not retarding) then filling up with 98 and six bottles of Octane Boost won't do jack.
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with specific regards to the:
"Your ECU picks this up way before you will hear it and retards ignition. You'll notice it as a loss of power"
i though by retarding or advancing the ignition, no net power loss/gain can be achieved? - i though you will just change the rev point where max power is achieved?
by the way...this was posted on an aussie site..so 95 and 98 RON ratings is what we get here - not sure how it compares with US RON ratings...most probably different..as i hear you premium fuel has a RON rating of low 90's
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There's a massive misconception going around about what octane actually means. Octane is actually a measure of a fuels resistance to burning. The higher the octane, the higher the resistance. By that measure you could say water has an octane of several 1000.
In any given engine running at optimal conditions there would be no difference in power running 98 or 95 octane fuel.
The difference comes about outside optimal conditions, such as on a hot day after idling in traffic for 20 minutes. Under these conditions a low octane fuel is more likely to detonate. Your ECU picks this up way before you will hear it and retards ignition. You'll notice it as a loss of power. In these sorts of conditions a higher octane is better.
But if your car runs fine on 96 octane (is not retarding) then filling up with 98 and six bottles of Octane Boost won't do jack.
--------
with specific regards to the:
"Your ECU picks this up way before you will hear it and retards ignition. You'll notice it as a loss of power"
i though by retarding or advancing the ignition, no net power loss/gain can be achieved? - i though you will just change the rev point where max power is achieved?
03-27-2002, 06:05 AM
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Re: fuel octane ratings - and the effects of... (dallandra)
I don't know if I'd call it 'resistance' to burning, it's more like a rating of the temperature the fuel will burn. So a lower octane fuel will burn at an earlier temperature than higher octane one. With high compression engines like ours you want high octane since high compression = more heat.
I would say under all conditions low octane fuel can detonate (and would in high compression engines). I do agree though, if your car is running fine on 93 octane that running 98 octane would be useless.
I don't know about Preludes, but my brother knows a guy with a Type R who gained 7whp by advancing his ignition timing.
I would say under all conditions low octane fuel can detonate (and would in high compression engines). I do agree though, if your car is running fine on 93 octane that running 98 octane would be useless.
i though by retarding or advancing the ignition, no net power loss/gain can be achieved? - i though you will just change the rev point where max power is achieved?
03-27-2002, 05:15 PM
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Re: fuel octane ratings - and the effects of... (dallandra)
Yes, as I understand it higher octane is beneficial in the conditions when the ECU decides to retard ignition timing or to prevent detonation. I've ran 94 octane in canada before and I felt that my car ran noticably smoother...
03-27-2002, 08:21 PM
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Re: fuel octane ratings - and the effects of... (Mike95lude)
On a Simmular note I heard from my local gas station (mobil, oh yea..) that soon all gas will come w/ ethanol! 
Usually when gas does it's 10% ethanol, so that sux. The reasoning behind these tree huggers plot is that it suppposedly burns cleaner and leaves a nice sticky black resadue on my valves. Either way because of this all of our cars will get crappier fuel econmy and will run worse. The gas station dude suggested that I run colder plugs. Oh and he said that all stations will soon be using ethanol, which is made at a higher boiling point of petroleum, so this is part of the reason that we will get to pay a little more for our gas. Looks like I will be buying my ethanol free gas in barrels and I'm going to get some real gas, I'm thinking 100 octane, muhahaha!!!
Usually when gas does it's 10% ethanol, so that sux. The reasoning behind these tree huggers plot is that it suppposedly burns cleaner and leaves a nice sticky black resadue on my valves. Either way because of this all of our cars will get crappier fuel econmy and will run worse. The gas station dude suggested that I run colder plugs. Oh and he said that all stations will soon be using ethanol, which is made at a higher boiling point of petroleum, so this is part of the reason that we will get to pay a little more for our gas. Looks like I will be buying my ethanol free gas in barrels and I'm going to get some real gas, I'm thinking 100 octane, muhahaha!!!
03-28-2002, 09:08 AM
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Re: fuel octane ratings - and the effects of... (mattmw88)
Here are the facts:
Octane is a measure of how fast the flame front travels in the fuel air mixture. Low octane fuels burn faster than high octane fuels and there is slightly more energy per gallon in low octane fuels. However, the rapid burning of the low octane fuel causes detonation in high compression engines or in engines where the timing is advanced.
As everyone knows higher compression and more timing advance mean more power, thus higher octane is required to slow the combustion process so that detonation doesn't occur.
Ethanol (or grain alcohol) is an extremely good fuel, actually much better than gasoline. It has a high octane rating and burns clean. It also absorbs more energy when it evaporates tends to cool the fuel mixture more than gasoline does Alcohol has two basic problems. The energy content is nearly half that of gasoline, i.e. you must burn nearly twice as much and it is hygoscopic (absorbs water and creates corrosion in the fuel system).
Octane is a measure of how fast the flame front travels in the fuel air mixture. Low octane fuels burn faster than high octane fuels and there is slightly more energy per gallon in low octane fuels. However, the rapid burning of the low octane fuel causes detonation in high compression engines or in engines where the timing is advanced.
As everyone knows higher compression and more timing advance mean more power, thus higher octane is required to slow the combustion process so that detonation doesn't occur.
Ethanol (or grain alcohol) is an extremely good fuel, actually much better than gasoline. It has a high octane rating and burns clean. It also absorbs more energy when it evaporates tends to cool the fuel mixture more than gasoline does Alcohol has two basic problems. The energy content is nearly half that of gasoline, i.e. you must burn nearly twice as much and it is hygoscopic (absorbs water and creates corrosion in the fuel system).
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