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Thread: maximum compression ratio with 98 octane fuel?

  1. #1

    maximum compression ratio with 98 octane fuel?


    Choosing parts and strategy on new engine build based on 7R small spigot case.
    I have to find save compression ratio for the fuel quality in the netherlands.
    We have on all pumps 95 octane and on many even 98 octane!

    What would be the maximum CR if I will limit myself to a 2.5 liter engine?
    Will be on webers IDA40 to start and maybe later on MFI in combination with mod S cams.

    I am interested in max CR with or without twinplug.
    I have been searching in the threads but difficult to find info as much is related to US fuel quality


  2. #2
    Member #226 R Gruppe Life Member #147
    Join Date
    Feb 2009
    Portland, Oregon
    I couldn’t answer that without knowing how your 98 compared to our USA fuel octane numbers. G

  3. #3
    98 RON (Euro) is approx 93-94 (R+M)/2 (US).
    95 RON (Euro) is approx 90-91 (R+M)/2 (US).

  4. #4

    I did not realize that there was a difference....
    hope this helps to answer my question on what is still save and with/without twinspark.

  5. #5
    In the UK I run a 2.7 litre with 10.3 :1 compression with twin spark. It runs on 95 Ron (5% ethanol minimum). Also I have a stock (single spark) 2.2 S which I believe to be 9.8:1. Bear in mind that in Europe there is likely to be an increase in ethanol content in fuel over the next few years.

  6. #6
    Member #226 R Gruppe Life Member #147
    Join Date
    Feb 2009
    Portland, Oregon
    10:1 single plug, 10.5 twin plug.

  7. #7
    I run 10:1 single plug.

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