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Old 09-21-2010, 10:45 AM   #1
Vanspeed
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Default what gas do you run?

I usually use unleaded regular in my car but I notice when I fill up, the car runs strange for a bit, then clears up. I am talking about 89 octane. What do you use and what is recommended for stock model a's with a 5.5 head?
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Old 09-21-2010, 12:01 PM   #2
1931 flamingo
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Default Re: what gas do you run?

run 87 with some MMoil occasionally
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Old 09-21-2010, 12:06 PM   #3
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Default Re: what gas do you run?

No need for high Octane with a low compression engine by todays standards. Pat Goss the Car Radio god, says 89 has less energy then 87. And dont forget the MMO.
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Old 09-21-2010, 12:18 PM   #4
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Default Re: what gas do you run?

To follow up A-Jay here is a link that explains octane.

http://auto.howstuffworks.com/fuel-e...question90.htm
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Old 09-21-2010, 12:39 PM   #5
J Franklin
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Default Re: what gas do you run?

I use regular pump gas since the ethanol has no effect on the A as there are no rubber parts in the fuel/carb system. don't leave ethanol set for long times tho as it attracts water and separates. I drain my tank for storage.
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Old 09-21-2010, 12:54 PM   #6
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Default Re: what gas do you run?

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Quote:
Originally Posted by A-Jay View Post
No need for high Octane with a low compression engine by todays standards. Pat Goss the Car Radio god, says 89 has less energy then 87. And dont forget the MMO.
Pat Goss is wrong. Gasoline octane is in general not related to energy content, however some high octane gasoline blending components are denser. It is only an indication of pre-detonation(ignites before top dead center at lower pressures) in engine combustion chambers. If anything mid-grade has slightly more energy as it probably has more reformate in it which is slightly more dense than average. The major gasoline blending component by volume that is high octane is reformed naphtha(reformate) with an octane of 93-104. The reformate is higher octane because of the aromatic benzene, toluene, and xylenes that reforming creates from cyclohexanes. Aromatics like benzene(7.33 lbs/gallon) are slightly denser meaning more energy than paraffins like cyclohexane(6.5 lbs/gallon). But you are only talking 15% more reformate to get a 2 octane boost which is only a very slight increase in density. The other major component of gasoline by volume is fluid catalytic cracked gasoline which hovers around 87 octane. I retired with 31 years as a Chemical Engineer last year at an ExxonMobil Refinery.

BTW octane for gasoline in the Model A era was around 70-75. BTW one reason diesel cars get better milage than gasoline ones is that diesel fuel weighs more per gallon than gasoline.

Last edited by mrtexas; 09-21-2010 at 02:10 PM.
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Old 09-21-2010, 12:56 PM   #7
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Default Re: what gas do you run?

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Originally Posted by Jeff/Illinois View Post
87 Octane, try to avoid Ethanol, and add some Marvel Mystery Oil because of today's 'dry gasoline' blends.

Never had a problem everything runs fine.
What do you mean by 'dry gasoline?'
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Old 09-21-2010, 01:54 PM   #8
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Default Re: what gas do you run?

no lead for lube , my guess .................. steve
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Old 09-21-2010, 05:17 PM   #9
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Default Re: what gas do you run?

I have been running on 91-93 and car runs fine.
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Old 09-21-2010, 08:21 PM   #10
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Default Re: what gas do you run?

I pump ethel
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Old 09-21-2010, 08:29 PM   #11
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Default Re: what gas do you run?

Quote:
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I pump ethel
If they run out of Ethyl I use Mabel.
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Old 09-21-2010, 10:01 PM   #12
Michael in Sedona
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Default Re: what gas do you run?

87 Octane, and a little MMO when I remember. Both of mine have HC heads and seem to run fine on that.
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Old 09-21-2010, 10:33 PM   #13
Dennis L Oberer
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Default Re: what gas do you run?

Here in Wisconsin if you use the highest octane it costs more but does NOT contain ethanol and so does not phase separate and so you can leave the gas in the car for months at a time and not have water issues in your fuel.

I run that in the coupe and have had ZERO problems.

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Old 09-22-2010, 03:23 AM   #14
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Default Re: what gas do you run?

96 Octane although I'm not completely convinced it runs any better on this than the cheaper 91
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Old 09-22-2010, 08:03 AM   #15
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Default Re: what gas do you run?

I've run all grade and octanes of fuel with no noticeable difference in performance in the "A".

When is gets closer to winter storage time, I start filling up with Shell 91, as it is not supposed to contain ethanol, which according to numerous comments, does not store well?
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Old 09-22-2010, 04:06 PM   #16
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Default Re: what gas do you run?

Marine Grade 89. No Booze in the mix.
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