Why Does Higher Octane Make More Power?
03-28-2004, 09:03 PM
#12
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Originally Posted by defprun' date='Mar 28 2004, 10:01 PM
Than regular gasoline being slower burning and therefore better for a N/A application is a myth?
03-28-2004, 09:12 PM
#14
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Gas is made of hydrocarbons. These come in different sizes and have different names based on the number of carbon atoms in the string. You've got pentane with 5 C atoms, hexane with 6 atoms, heptanes w/ seven, octane 8, etc. Hexane is the most prevalant hydrocarbon in gas. Back in the day the octane rating literally meant how much octane was in the gas.
Octane needs a higher temperature to ignite than hexane which is a good thing if you have an engine that has conditions that would be more prone to detonation. People got smart and started to use additives, i.e. lead, to raise the temp required to ignite the fuel. Consequently, the gas that you buy at your local shell or citgo is all the same. The only difference is the additives mixed with the fuel so they all basically burn nearly equally efficient but your premium need higher temps to burn than your regular fuel. You don't get more power out of any given sort just a different ign. temp.
Of course, engines are designed for different applications, therefore, some run better with a fuel that burns at a lower temp. and some better with one that burns at a higher temp. This is my take on octane.
Octane needs a higher temperature to ignite than hexane which is a good thing if you have an engine that has conditions that would be more prone to detonation. People got smart and started to use additives, i.e. lead, to raise the temp required to ignite the fuel. Consequently, the gas that you buy at your local shell or citgo is all the same. The only difference is the additives mixed with the fuel so they all basically burn nearly equally efficient but your premium need higher temps to burn than your regular fuel. You don't get more power out of any given sort just a different ign. temp.
Of course, engines are designed for different applications, therefore, some run better with a fuel that burns at a lower temp. and some better with one that burns at a higher temp. This is my take on octane.
03-28-2004, 11:16 PM
#18
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Join Date: May 2002
Location: California
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well i dont claim to be right, but this is what we were talking about this afternoon.
all things being equal you want max cylinder pressure at around 20-35* degrees atdc, on the power stroke. this is where the crank has the most leverage on the crank.
with either low or high octane you can get this by adjusting the timing, in our theory. if we can adjust the timing, then burn speed is irrelevent, because we can set the timing to account for it.
higher octane, means the mixture wont detonate as easily, or it can absorb more heat before it explodes (detonates). it also may contain more btus
so higher octane give more power because it has more btu's.
all things being equal you want max cylinder pressure at around 20-35* degrees atdc, on the power stroke. this is where the crank has the most leverage on the crank.
with either low or high octane you can get this by adjusting the timing, in our theory. if we can adjust the timing, then burn speed is irrelevent, because we can set the timing to account for it.
higher octane, means the mixture wont detonate as easily, or it can absorb more heat before it explodes (detonates). it also may contain more btus
so higher octane give more power because it has more btu's.
03-29-2004, 06:13 AM
#19
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I talked to a guy from speedsource and he was telling me that after hundreds of dyno time tuning the new rx8's that they had only found 1 fuel, that cost 16 dollars a gallon, that made more power than 87 octane grandma pump gas. If that tells you anything.
03-29-2004, 01:43 PM
#20
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Location: Austin, Texas
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But burn speed is *not* irrelevent because it has the same speed regardless of engine speed. So that means at higher RPM there is less time for the charge to reach max expansion, so you need to ignite it sooner. timing = important 