gas
Tuned
Joined: Mar 2011
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Also known as pre-ignition. It's when the air/fuel mixture ignites prior to the piston reaching the top of it's stroke. Lower octane fuels are prone to it in high compression engines, which is why high performance vehicles usually require premium unleaded.
Junior User
Joined: Aug 2010
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MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
As has been said, octane rating is a measure of how much the fuel can be compressed before it self-ignites. High-compression engines require a higher octane rating so that the fuel can be compressed more tightly without self-detonating. An old smog motor, which would be the case for a '78 400, has relatively low compression and can run just fine on 87. Octane rating has nothing to do with detergents.
Elder User
Joined: Apr 2011
Posts: 632
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From: Bremerton, Wa
Actually,
That is a great question.
Now, this thread is gettong useful
That is a great question.
As has been said, octane rating is a measure of how much the fuel can be compressed before it self-ignites. High-compression engines require a higher octane rating so that the fuel can be compressed more tightly without self-detonating. An old smog motor, which would be the case for a '78 400, has relatively low compression and can run just fine on 87. Octane rating has nothing to do with detergents.
Senior User
Joined: Jun 2011
Posts: 146
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From: Bristow, VA
Just for clarification there was no intent to mislead you on the way detergents are added to gas, in rural counties with Mom & Pop stations some of them can opt to add the detergents to keep down costs. Ask some of them and they will tell you they do. In larger citys the gas comes form a truck, most of which have 4 compartments ranging from 1750 - 2500 gals per container with different octane fuels in each. This is just one reason for the varying prices in gas from station to station. The time/distenace it takes for trucks to make the deliveries is another. Owners do what they can to offset the cost of the fuel and turn a profit. This is from someone I know that ownes a couple of Mobile stations, with and without garages. Take it for what its worth.
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JAM66
2.6, 2.8, 2.9, 4.0 & SOHC 4.0 V6
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Aug 23, 2006 10:44 AM
