what gas do you run?

Vanspeed

Vanspeed

Well-known member
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?
 
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.
 
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.
 
A-Jay said:
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.
Click to expand...

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.
 
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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.

Dennis L Oberer
Green Bay WI
 
96 Octane although I'm not completely convinced it runs any better on this than the cheaper 91
 
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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