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EGT Distance Impact

in 912 / 914 Technical Questions 6 years ago
I have a Highlander with a 912ULS with an EGT on each side in the rear cylinders. I was starting to play with the needle and main jet as I’m seeing 1375 at WOT and 1450 at partial throttle. However, I noticed the EGTs were placed at about 70mm (2 3/4”) instead of the manual stated 100mm (3.94”) distance from the flange. I could move them, but it’s kind of a PITA. Does anybody know the impact of having the EGTs 30mm (1.25”) closer? About 100F higher? Maybe just shoot for 1550 EGT and then check the plugs to see if they are a nice beige?

8122F0CB-1970-4859-98AE-E3BF786766FD.jpeg (You do not have access to download this file.)

  • Re: EGT Distance Impact

    by » 6 years ago

    There is nothing wrong with your temps. They are well within normal. Could the EGT probe be a little more out to the correct measurement, sure, but it seems to be fine. Unless you're having some kind of issue with rich running i.e. operating and living at high altitudes why mess with it. The colder denser air will also make it run a tad leaner. Unless you have a specific need to play with the needle I'd leave it in the #3 position. Any dry black soot you may see is from idling. When running up at cruise rpms this is all burned off.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: EGT Distance Impact

    by » 6 years ago

    Just for a point of reference...

    The 912-U series engines call for 100mm EGT placement and 1616°F Max.
    The 912-i series engines call for 50mm EGT placement and 1742°F Max.
    The 912-i series engines operate Leaner by design.

    You are under 1500°F.
    If it "Ain't" Broke, Don't Fix It!

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Guilherme Tomazini
      
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  • Re: EGT Distance Impact

    by » 6 years ago

    I agree with Bill. It ain't broke.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: EGT Distance Impact

    by » 6 years ago

    Ok, fair enough to not fix something that isn’t too broken. It seemed a little leaner at partial throttle vs. wot to justify going richer on the needle, but then after doing that it’d be too rich overall. Is that typical to have partial vs wot be 100F richer on EGTs?

    Thanks on the 912i EGT placement. I didn’t know it was at 50mm, it is closer and hotter. And, somewhat apples to oranges as it’s injected.
      
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  • Re: EGT Distance Impact

    by » 6 years ago

    Mid range on the throttle can produce slightly higher EGT's because it's leaner there. It is richer at high rpm to help protect the engine. You shouldn't be flying around with in the 4K rpm range as your constant cruise rpm. It wasn't designed for that.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

    Thank you said by: Guilherme Tomazini
      
    Report
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