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Thread: What fuel / octane to use?

  1. #1
    Senior Member 72911E's Avatar
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    What fuel / octane to use?

    Does your early 911 run on high octane? run ok on 95?

    Thanks
    Derek

  2. #2
    Quote Originally Posted by 72911E
    Does your early 911 run on high octane? run ok on 95?

    Thanks
    Derek
    My 1973 911E with 2.7RS-spec engine runs on Regular (87). I use Premium (93) when I play at the track.
    Jim Richards
    Aubergine 1973 911E Sunroof Coupe w/ 2.7RS MFI
    Early 911S Registry Member #589
    GruppeB #911

  3. #3
    Senior Member MoparBoy72's Avatar
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    Derek,

    Our engines tend to be considered lower compression and will run on 87 just fine. I doubt your E motor will see any benefit from 95 Octane fuel. If you have different than stock pistons like JimR you would benefit from higher octane fuel.

    I run my E on mid grade (89) with very nice results. A stock motor will have very little benefit from higher octane fuel.
    -Andrew
    '72 911E
    '82 931, '92 968, '93 968
    S Reg #1074

  4. #4
    Your stock '72 911E should have a compression ratio of 8.5:1. You can run all day on 87 octane fuel. Anything higher will just send a portion out the tailpipe as unburnt fuel. If there is carbon build-up in the combustion chamber and you hear the resulting knock, go to the next higher octane level (mid-grade in this instance).
    Peter Kane

    '72 911S Targa
    Message Board Co-Moderator - Early 911S Registry #100

  5. #5
    Senior Member rgrimm's Avatar
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    Most, if not all of the mid-grade in our market (89) is ethanol...
    Roger
    68 Sand Beige 911 Coupe #11830091
    84 Moss Green 911 Carrera

  6. #6
    Luft gekuhlt Bummler's Avatar
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    I believe there are thirteen different formulations distributed throughout the US. Most of it is predicated on the states requirements and the season.

    http://www.epa.gov/otaq/rfg/whereyoulive.htm#required

    Definitions of Gasoline Grades

    The classification of gasoline by octane ratings. Each type of gasoline (conventional, oxygenated, and reformulated) is classified by three grades - Regular, Midgrade, and Premium. Note: Gasoline sales are reported by grade in accordance with their classification at the time of sale. In general, automotive octane requirements are lower at high altitudes. Therefore, in some areas of the United States, such as the Rocky Mountain States, the octane ratings for the gasoline grades may be 2 or more octane points lower.

    Regular Gasoline: Gasoline having an antiknock index, i.e., octane rating, greater than or equal to 85 and less than 88. Note: Octane requirements may vary by altitude.

    Midgrade Gasoline: Gasoline having an antiknock index, i.e., octane rating, greater than or equal to 88 and less than or equal to 90. Note: Octane requirements may vary by altitude.

    Premium Gasoline: Gasoline having an antiknock index, i.e., octane rating, greater than 90. Note: Octane requirements may vary by altitude.
    Stefan Josef Koch
    RGruppe #194/SRegistry #1063
    1969 Porsche 911E, Light Ivory (38 years and counting)
    2015 Porsche Cayman S
    2012 BMW R1200GS, 1973 BMW R75/5


    "An intelligent man is sometimes forced to be drunk to spend time with his fools." -E. Hemingway

  7. #7
    I assume we are talking about the US calculation of octane here: (RON+MON)/2. Derek, where do you live? 95 octance in the UK and continental Europe means something very different to the US based numbers quoted above.
    Kenik
    - 1969 911S
    - 1965/66 911
    - S Reg #760
    - RGruppe #389

  8. #8
    I am not aware of any 95 octane as rated in the US being sold at any pump in the US at least not as a std. grade of gasoline ie premium unleaded. You will find premium rated anywhere from 90 to 93 but no 95. I have seen a few select stations sell 100 grade racing gasoline. Where are you seeing 95? I know premium in some countries in euro can be as high as 98 but again that is a different rating system than US. Have heard leaded gasoline is still available too?
    Early 911S Registry #750
    1970 911E - The Good Stuff
    2001 Toyota Landcruiser

  9. #9
    In Scandinavia and northwest Europe we use 92/95/98 octane fuel. Most "sportscars" run 98. In eastern Europe lower octane fuels are more common. Not sure if or how octane numbers in Europe compare to US octane numbers.

    John
    Early 911S Registry #931
    --------------------------------
    1971 911 2.2S Coupe Albert Blue
    1971 911 2.2T Coupe Tangerine
    2005 997 C2S Coupe special 1965 slate grey
    1978 911 3.0 SC Targa Silver w/chrome trim

  10. #10
    Luft gekuhlt Bummler's Avatar
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    Europe uses RON or research octane, the measurement derived under optimal test conditons determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

    As Kenikh noted the US puts an AKI (anti knock index) number on the pump (R+M/2) an average of the RON and MON (motor octane). Motor octane is a measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance.
    Stefan Josef Koch
    RGruppe #194/SRegistry #1063
    1969 Porsche 911E, Light Ivory (38 years and counting)
    2015 Porsche Cayman S
    2012 BMW R1200GS, 1973 BMW R75/5


    "An intelligent man is sometimes forced to be drunk to spend time with his fools." -E. Hemingway

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