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Polishing intake manifolds

in General Tech Discussion 6 years ago

  • Re: Polishing intake manifolds

    by » 6 years ago

    Fellow Flyers,
    I finally did the enlarged balance tube mod on my 912UL over the last couple weeks and have flown for about 2 hours now and can firmly confirm that:
    -It runs very smooth over the full throttle range
    -No change in my performance numbers except that it feels lot smoother overall. (it feels more powerful)
    -Cold start is like a car with no shudder or vibration.

    Not enough time to say if it changed my fuel consumption but I would assume it will run more efficient just because of all that smoothness and both banks running hand in hand.

    I will remember to take some pictures next time but all I did is that I drilled and taped the existing balance tube holes to 3/8"NPT and screwed in the 3/8" 45 degree male to female fittings in them. I drilled out the fittings ID to remove any casting imperfections and increase the ID a bit.Then I took a 3" long 3/8" NPT nipple and cut it in 2 halves. Screwed each half into the fittings added. Connected both sides with a 9/16" Vacuum hose from PartSource. All fittings were thread locked on final assembly.
    Feel free to contact me with any questions and I will consider doing all the machining and supply parts as kit for anyone who would like to give it a try for something around $300.

    Happy Skies,
    Harry
    Thank you said by: Eugene Klimenko
      
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  • Re: Polishing intake manifolds

    by » 6 years ago

    Please post some pics. Thanks in advance.
      
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  • Re: Polishing intake manifolds

    by » 6 years ago

    I don't mean to be skeptical odd man, but after years of research on other projects and props that people swear by, without instrument testing and real time test facts I found many of the proposed gains by some owners to just be wishful thinking.
    You want it to work so bad and some have said how great it is that when you do it it is great, but with instrument fact checking it's no different than it was before the modification.
    You need to have made test with instruments before any modifications and then repeat those test under identical circumstances. Then you need to put on a few thousand hours to see about any long term affects good and bad. There has only been a few owners that have gone to the larger cross over tube. Some swear by it others removed it later on. None ever used test instrumentation to back up any claims.

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

      
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  • Re: Polishing intake manifolds

    by » 6 years ago

    I think the larger balance tube has already been proven to have many benefits and ROTAX would have done this if they had not moved on to the 912si. Here is a link to a product that list the benefits of the larger tube. In my 8 years experience with the 912ULS vibration is a problem that wears on everything attached to the motor. Savings could be realized over time to justify this modification. Also I do not think experimentation should not be discouraged as it is the driver of new products/enhancements.
    https://www.flygas.info/2017/06/18/311/
      
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  • Re: Polishing intake manifolds

    by » 6 years ago

    I am going to have to agree with Roger. Without proper data showing the difference it's very difficult to argue.
    I have been working with Rotax a bit myself. I feel that increasing the size of the tube is simply trying to cover up out of sync carbs.
      
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