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Thread: Precision tuning the Rotax 912 UL/ULS

  1. #91

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    Default Re: Precision tuning the Rotax 912 UL/ULS

    I am at exactly 12.8 at WOT so that is good. This is important as you say to get power

    Cruise now at 15 and it runs fine there too. Lean stuttering now gone at cruise which was priority. Much better than it was. I only cut off two coils from the springs but it was an improvement. Supports the vacuum theory. Might try cutting off one more coil later or not, for now I am happy and plane is operative.



    Quote Originally Posted by AvDES LLC View Post
    runs fine and most efficiently are two very different things. The engine shouldn’t bog when seeing the numbers you’re providing, but you’re also not pulling peak power at any rpm in which your ratio is outside of 12.8 to 13.1 ( I believe the scientifically proven upper threshold is actually more around 14 but I aim for that 13.1 for consistency).

    those FI systems are very nice, but I’m with you - I cannot justify that level of expense for my little 80hp sky dirt bike. Maybe if there was a way to make some of that money back, but since I’m no competitive racer or silver spoon child, I’ll stick with the carbs for now haha
    Last edited by trond; 01-13-2023 at 10:24 AM.

  2. #92
    Senior Member jiott's Avatar
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    Default Re: Precision tuning the Rotax 912 UL/ULS

    I wonder what the AFR numbers are thru the rpm range for a 912 with Edge EFI system, or for that matter what they are for a 912is? Would be interesting to put an AFR meter on those engines-maybe someone already has?
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #93

    Default Re: Precision tuning the Rotax 912 UL/ULS

    Quote Originally Posted by jiott View Post
    I wonder what the AFR numbers are thru the rpm range for a 912 with Edge EFI system, or for that matter what they are for a 912is? Would be interesting to put an AFR meter on those engines-maybe someone already has?
    apart of those systems REQUIRES that an AFR meter be in place. The computer “sniffs” with the O2 sensor and adjusts the parameters as far as pulse peak width and duration in an effort to hit the AFR the system is set to operate at. I cannot make any statements for edge, however I can make statements as far as BDTurnkey’s Yamaha conversion EFI controller and I know for 100% certainty that system is set to operate at exactly 12.8 to 13.1.

  4. #94

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    Default Re: Precision tuning the Rotax 912 UL/ULS

    325024110_500402275532697_8151983764044584091_n.jpg

    This an from the dyno. 912 ULS with big bore kit and Edge EFI

    Quote Originally Posted by jiott View Post
    I wonder what the AFR numbers are thru the rpm range for a 912 with Edge EFI system, or for that matter what they are for a 912is? Would be interesting to put an AFR meter on those engines-maybe someone already has?

  5. #95

    Default Re: Precision tuning the Rotax 912 UL/ULS

    Thank you for posting that! Looks like their range is 12.2 to 13.4 at the extremes. Depending on sampling rate of the system it could also be that the data samples were pulled at major peaks / valleys and those points were attempting to be corrected by the system at that instant. Either way this looks to align with the numbers I remember from many many moons ago when I was a kiddo being taught this stuff by Grandpa and Uncle T.

  6. #96

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    Default Re: Precision tuning the Rotax 912 UL/ULS

    it certainly looks great. Awesome system. Obviously this is at static and does not show cruise values that are bound to be leaner

  7. #97

    Default Re: Precision tuning the Rotax 912 UL/ULS

    Why would you say that cruise values are bound to be leaner? Interested in your thought process on this one.

  8. #98

    Default Re: Precision tuning the Rotax 912 UL/ULS

    Ah. Thanks for the response. I’m aware of the 3D maps, I thought you had some first hand insight / knowledge into the Edge system that the rest of the world isn’t privy to about their maps or settings. I see now it’s just based off of the standard tuning assumptions.

  9. #99
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    Default Re: Precision tuning the Rotax 912 UL/ULS

    I know many that are running the edge efi and love it on their 912ULS. If it was in the budget the first thing I would do to the 912uls is put EFI on it. The guys that have done it say how much smoother the engine runs. Starts like a modern engine. Freezing cold, burning it hot, they don't care. You can richen up the lean midrange and lean out the rich ends. Keep in mind the dyno chart you listed is for a turbo 912uls (edge915) so the AFR are a little different. The 912is and 915is are trying to acheive peak fuel efficiency so rotax runs them very lean imo. Also turbo engines needs richer AFR's to help stay away from det.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  10. #100

    Default Re: Precision tuning the Rotax 912 UL/ULS

    100% agreed that a FI system will be leaps and bounds above tinkering with carbs to get them into "best range". Another thing I find very interesting is the differences in "mission" that people have with these aircraft - some are worried about peak fuel efficiency which is not peak power whereas I am one of the individuals that is tuning for peak power and not really taking fuel efficiency into consideration. Depending on the goal of the plane - short back country strips with rising terrain and mountains on either side is the kinda flying i play with and in these instances I want as much power as possible at that prop, not best fuel efficiency. If I had the desire to go FI for the consistency and the ability to tinker with the maps, id still likely aim that system toward the 12.8 - 13.1 AFR that I continue to mention - that would give the best of both worlds from the smooth engine perspective while still keeping that engine in a fueling range that provides maximum cylinder cooling and power simultaneously. Just my .02

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