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Old 07-10-2010, 06:10 PM   #1
Blackstone
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non premium use for cobra

For normal cruising and around town driving, has anyone had extensive experience using 87 octane instead of 91? I tried one tankful and couldn't detect anything unusial. Engine damage issues? I have also a 2000 lincoln Cont with the 32 valve engine and have tried the same unleaded without hearing anything unusual.
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Old 07-11-2010, 10:50 AM   #2
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Be careful ... some cars will start to skip, stutter, and some will even shut down. I don't think that I would take a chance over 10cents a gallon.
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Old 07-11-2010, 04:19 PM   #3
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early detonation will be cause by using under 91 octane when the manufacture tells you to use it. It will melt rings and other things. I would never consider using anything other than premium with any car that takes it, especially a supercharged one. it being supercharged raises the chance. do not listen to anyone who says " oh i have been running 87 octane for a while without a problem." they have a problem. they just dont know it. and people do use 87 all the time in premium cars. and people ruin engines all the time in premium cars.
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Old 07-18-2010, 11:31 PM   #4
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I wouldn't. My buddy has a C-5 vette and does...why I don't know. Save a few nickles on gas < detonation potential IMO.
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Old 07-27-2010, 04:53 PM   #5
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Octane values represent the combustion level ie 87 has a lower combustion temp than 91 and so forth 93 higher. What that is doing is keeping the combustion level in the combustion chamber high so the gas doesn't ignite before the spark sets it off. Using a lower octane in high performance engines is a no no. What happens as the piston travels up compressing the air fuel mixture it can ignite from the compression before the piston has traveled to its upward position causing the ignition to go against the travel of the piston motion (reversing) while all the other cylinders are still going forward at which point something is going to break.
Also termed dieseling because there are no spark plugs in diesel engines they fire from the compression of the air fuel mixture in the cylinder.
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Old 07-27-2010, 08:45 PM   #6
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C-5 Corvette ... not supercharged so not as much heat for detonation. It would be safer in his engine than in the Cobra. You also have to factor in the Chevrolet thing ... not too bright to skimp when the car costs that much.

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Originally Posted by ohiiicobra
I wouldn't. My buddy has a C-5 vette and does...why I don't know. Save a few nickles on gas < detonation potential IMO.
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Old 01-03-2011, 11:22 AM   #7
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For starters, fuel with a lower octane rating are less stable and more prone to detonation under compression. Octane is a hydrocarbon molecule in gasoline which has a stable molecular bond when compared to the other hydrocarbon molecules found in gasoline. The higher amount of Octane the lesser amount of preignition or detonation. Also, since the computer used in the 04 or earlier models is not very fast it will not compensate for the change in Octane fuels like the newer vehicles will. Not sure if ford installed knock sensors on the 03/04 model years (believe the supercharger noise was a reason why they were omitted). The newer computers used since 05 have the capacity to detect knock and adjust fuel ratio to prevent detonation regardless of what grade fuel is used. Recommended fuel grade is premium 91+. Like others said, the extra cost for premium fuel is less than the cost to replace/repair a damaged engine.
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Old 01-08-2011, 08:37 AM   #8
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I work for a large oil producer (not Shell), but work in the petrochem side of the business. I have asked folks on the gas and oil side what is the best premium gas to use in my Cobra and Shell is mentioned.
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Old 01-22-2012, 01:55 PM   #9
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One other comment, since the 03/04 Cobras use old technology in the CPU (processor speed is too slow) I would would not use low octane fuel.

On newer models (just about any make) with the more advanced CPU systems, they can detect grade of fuel while the engine is running. My Toyota FJ Cruiser for example requires 91 Octane fuel. Although it is not recommended, I can safely run lower octane fuel but at a compromise to fuel economy. It will run rich when using low Octane fuel. The newer models after 2010 will operate efficiently with the low Octane fuel since the programming of the CPU and addition of other sensors can prevent detonation before it happens.
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