What spark plugs with a Siebenrock kit on R75/5?

Discussion in 'Airheads' started by jjwithers, Nov 15, 2020.

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What spark plugs with a Siebenrock kit on R75/5?

  1. W5DC

    33.3%
  2. W6DC

    33.3%
  3. W7DC

    33.3%
  1. jjwithers

    jjwithers Been here awhile

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    I’m not concerned about other plug brands, this is a survey based on heat range and what plugs to run with a R75/5 and Siebenrock kit making the engine close to 1000cc.
    #1
  2. Arktasian

    Arktasian Turbo Cum Laude

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    Plugs are inexpensive, engines & especially those modified tend to react uniquely (especially given overall range of factors)
    Suggest run in, then chop them for a view during suitable long hard run.
    #2
  3. Cogswell

    Cogswell Now living the new normal.

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    What's the estimated compression ratio of the new set up ?

    I have always started with one heat range colder plug on a performance build than specified for a stock motor.
    #3
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  4. Plaka

    Plaka Brevis illi vita est

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    ^^^^^^this.

    plug too hot = detonation = bad
    plug too cold = BFD

    so you want to run hwe coldest plug you can. a fresh top end will burn cleanly, hot plug not needed.
    #4
  5. pommie john

    pommie john Long timer

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    I don't use Bosch plugs, I use NGK so I can't contribute to the survey. But I have two airheads . The standard NGK plug is a BP6ES. In my mildly tuned road bike ( 9.5 compression, big carbs) I use BP7ES. In my full-on race bike with 10.5 compression, race cam and big carbs that gets thrashed to the red line every gear change I use NGK B8ES.
    So to sum up: stock engine use 6, mild tune use 7 , full race use 8.
    #5
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  6. Plaka

    Plaka Brevis illi vita est

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    which is hot and which cold?
    #6
  7. robtg

    robtg Long timer

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    With NGK 5 is hot, 10 is cold. Just the opposite of Bosch.
    #7
    Cogswell likes this.