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In the heavy maintenance manual there is a graph of throttle position versus "target" manifold pressure (see attached). In the installation manual there is a graph of rpm versus manifold pressure (I can't reproduce this curve on this computer).
If I plot the two graphs together (attached) knowing the different engine speeds for different throttle settings then the two graphs don't agree.

My manifold pressure seems to follow the speed curve but I don't understand what the "target" pressure graph is telling me.
Can anyone explain the value of this graph?

Mike G
  • Re: 914 manifold target pressure graph

    by » 11 years ago


    I managed to attach the attachments this time.
    Mike G
    Targetpressurepage.pdf (You do not have access to download this file.)
    manifoldpressures3.pdf (You do not have access to download this file.)

  • Re: 914 manifold target pressure graph

    by » 11 years ago


    I'm not surprised that nobody has answered, I've asked a lot of "experts" and none could help.
    I joined and paid to be a member of this forum in the hope that there is some way of asking Rotax my question.
    This Target pressure curve is in the manual so Rotax must have put it there for a reason.
    Is there any way of getting a reply from Rotax??
    Mike G

  • Re: 914 manifold target pressure graph

    by » 11 years ago


    Hi Mike,

    Sorry your having the problem with the answer, but there just isn't enough 914's out there to have as many experts as the 912 or the 2 strokes. Send me your email and I'll send you a special email.
    ssadiver1@yahoo.com

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


  • Re: 914 manifold target pressure graph

    by » 11 years ago


    Roger
    Thanks, I've sent my e:mail to you.
    The reason I'm asking this question, which may seem rather theoretical, is because I have a definite loss in power at 3200 rpm static and this occurs at exactly 15% throttle opening which is the point at which the "target" pressure drops and I can see the waste gate start to open at that point. This loss in power occurs at higher rpms when in flight but with a fixed pitch prop this is logical since at higher speeds the 15% throttle position will give a higher engine speed. So my question is because I have a real problem. speed.
    I've changed the throttle potentiometer and the French Rotax agent has recalibrated it with the TCU.
    Mike G

  • Re: 914 manifold target pressure graph

    by » 11 years ago


    Hi Mike,

    I sent you an email.

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


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