| Author |
Message |
    
Jess Brandt (Disco285)
| | Posted on Tuesday, October 22, 2002 - 11:29 pm: | 
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i have been putting the recommended octane in my truck since i got it about 6-7 months ago... i don't know what the other dude put in it but was curious what you guys though...my parents have owned a '97 disco and currently own a '00 and both have run on the highest octane (93) around here...just curious really...thanks, |
Erik Geagan (Geagan)
| | Posted on Wednesday, October 23, 2002 - 12:49 pm: |
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I've gone below 93 for a month and the engine was running a bit funny. That was enough for me to stick with the 93. It's worth it in the long run. |
Erik Geagan (Geagan)
| | Posted on Wednesday, October 23, 2002 - 12:49 pm: |
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I've gone below 93 for a month and the engine was running a bit funny. That was enough for me to stick with 93. It's worth it in the long run. |
Norm
| | Posted on Wednesday, October 23, 2002 - 08:58 pm: |
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According to the owner's manual for a '95 you should use 90 octane or above, the higher the better. I use 92 or 93 (when I can get it) -- 91 can usually be found everywhere.
---Norm |
rover
| | Posted on Wednesday, October 23, 2002 - 10:28 pm: |
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My engine actually seems to run better with 87 octane than 93. I have been using 93 since I bought it and for the last month i have been using 87, I seem to get better gas mileage and better acceleration. I know this seems backwards but this is what ive experienced. |
Jason Vance (Jason)
| | Posted on Thursday, October 24, 2002 - 12:48 am: |
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An increase in octane effectively slows down the burn of the air/fuel mixture within the combustion chamber. High compression ratio engines often require higher octane in order to reduce the chance/incidence of detonation. Because the burn of the air/fuel mixture is slower due to the high octane, the engine builder/tuner can maximize other engine parameters, such as compression ratio, ignition and cam timing to gain overall engine outputs.
Lower octane gas has a faster burning flame which can potentially offer gains in power and gas mileage, if and only if detonation does not occur (knock sensors are often employed to detect detonation because WE CANNOT ALWAYS HEAR IT!!!!).
So, what do you do? I'm assuming the later GEMS ignition employs a knock sensor to detect detonation and alter the ignition timing to prevent it. If this in fact is the case, running lower octane gas could cause the GEMS to retard the normal timing curve and detrement engine performance. Why? Because eventhough lower octane should give a faster burn, your ignition is less advanced (e.g. the process of retarding, not actually being retarded or AFTER TDC) and is not benefiting from the fuel. With the vacuum-advance distributor on earlier Discos, detonation can not be prevented...if it indeed is occurring (unless you retard the total advance, then you know that you have detremented performance already).
Should you be concerned about low-octane fuels? Probably not...plenty have run low octane without damaging the engines, but it is nonetheless important to understand why high octane fuel is recommended, and why people claim better performance with low-octane.
Car Craft did a big-block engine comparo a year or so back. The builds were fairly mild in CR and cam timing (less than 9.5:1 CR) and all engines put out significantly more torque and HP on 89 octane, than on 91 or greater (tested race gas, too).
Anyway, I run 91...FWIW (and sorry for the long post) |
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