Author Topic: Which gas, octane vs ethanol? 331  (Read 282 times)

Offline bullet bob

  • Posts: 103
  • Name: b beebe
Which gas, octane vs ethanol? 331
« on: June 20, 2017, 06:46:25 AM »
I can't find any 93 octane fuel around here that is non-ethanol. My choices are either 93 w/ethanol or 90 "pure". I'm leaning towards the 90 pure but would like your input. Fuel pump has been professionally rebuilt. Thanks all. Bob
Honda Goldwing 1800  "I don't need no stinkin' map, I've still got gas"

Offline cadman56

  • Posts: 341
    • CLC Member
      CLC Member #5820
  • Name: Larry Blanchard
Re: Which gas, octane vs ethanol? 331
« Reply #1 on: June 20, 2017, 07:22:24 AM »
I started using EO87 in my 91 Brougham and was thrilled at how much smoother the engine ran and power was increased also.  The wife has to do the driving and she even remarked at the difference.  See what others may say but I would give the pure gas a try.  Larry
1956 Cadillac Coupe deVille (sold)
1956 Cadillac Convertible (sold)
1956 Cadillac Eldorado Seville
1967 Cadillac Eldorado (sold)
1968 Cadillac Convertible
1991 Cadillac Fleetwood Brougham dElegance
Larry Blanchard CLC #5820

Offline Art Gardner CLC 23021

  • Posts: 1015
    • CLC Member
      CLC Member #23021
Re: Which gas, octane vs ethanol? 331
« Reply #2 on: June 20, 2017, 08:27:56 AM »
The 331 runs well on regular and doesn't need high-test fuel.  In fact, it won't help the engine run better at all.  Non-ethanol fuel (regular grade) is best for the 331, IMO...

Art G
Art Gardner


1955 S60 Fleetwood sedan

Offline bullet bob

  • Posts: 103
  • Name: b beebe
Re: Which gas, octane vs ethanol? 331
« Reply #3 on: June 20, 2017, 08:39:22 AM »
Appreciate that Art. The memory's not what it used to be, but I thought the 331's required 93. I suffer from CRS!
Honda Goldwing 1800  "I don't need no stinkin' map, I've still got gas"

Offline Art Gardner CLC 23021

  • Posts: 1015
    • CLC Member
      CLC Member #23021
Re: Which gas, octane vs ethanol? 331
« Reply #4 on: June 20, 2017, 09:32:36 AM »
No worries!  The 331 engine started out at something like 7.5:1 compression and increased over the years (starting with 52, i think).  They increased the compression ratio, while keeping the displacement the same, by decreasing the volume of the combustion chambers in the heads.  With the introduction of the 365 in 1956, the engine went to about 10:1 compression (maybe 10.5) and then needed hi-test fuel for sure.  The last 331, the 1955, had a compression ratio of about 9:1 and should be okay on regular fuel. Certainly, the early, lower-compression 331s from 1949-51 don't need hi-test.
Art Gardner


1955 S60 Fleetwood sedan

Offline T J Lankes

  • Posts: 37
  • Name: T J Lankes
Re: Which gas, octane vs ethanol? 331
« Reply #5 on: June 20, 2017, 12:59:19 PM »
You may already have this site for locating non-ethanol stations but here it is just in case you need it:

https://www.pure-gas.org/

Offline D.Yaros

  • The Gray Lady, a '55 Coupe de Ville
  • Posts: 772
  • Ed./Pub. Car Collector Chronicles
  • Name: Dave Yaros
Re: Which gas, octane vs ethanol? 331
« Reply #6 on: June 20, 2017, 03:55:54 PM »
Regular worked just fine for me in my 1955 331 c.i. engine.
Dave Yaros
CLC #25195
55 Coupe de Ville
92 Allante
62 Olds  

You will find me on the web @:
http://GDYNets.atwebpages.com  -Dave's Den
http://GrayLady.atwebpages.com -'55 CDV site
http://www.freewebs.com/jeandaveyaros  -Saved 62 (Oldsmobile) Web Site
The home of Car Collector Chronicles.  A  monthly GDYNets newsletter focusing on classic car collecting.
http://www.scribd.com/D_Yaros/

Offline bullet bob

  • Posts: 103
  • Name: b beebe
Re: Which gas, octane vs ethanol? 331
« Reply #7 on: June 20, 2017, 08:26:41 PM »
You may already have this site for locating non-ethanol stations but here it is just in case you need it:

https://www.pure-gas.org/
Thanks. I do have that. The only thing around here is at the lake. 90 octane. $3.79/gal.
Honda Goldwing 1800  "I don't need no stinkin' map, I've still got gas"

Offline Jay Friedman

  • Posts: 1641
    • CLC Member
      CLC Member #3210
Re: Which gas, octane vs ethanol? 331
« Reply #8 on: June 20, 2017, 09:04:24 PM »
90 octane is fine.  My '49 with a 331 runs perfectly on 87 octane non-ethanol fuel.
1949 Cadillac 6107 Club Coupe
1932 Ford V8 Phaeton (restored, not a rod).  Sold
Decatur, Georgia
CLC # 3210
"If it won't work, get a bigger hammer."