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Thread: Single 40mm Rotec TBI / 912uls zipper custom setup

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    Premium Member (Donated) GravityKnight's Avatar
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    Default Single 40mm Rotec TBI / 912uls zipper custom setup

    *I mentioned this latest project in another thread, but for information/reference purposes down the road I'll start a separate thread.

    Background
    Rotax's dual carb setup sucks pretty bad. In my opinion it's not for the reasons most people complain (carb sync, though that, along with double fuel lines, intake stuff etc. is a cluttered mess). It's because the crappy intake manifold design doesn't allow for equal fuel distribution across the throttle range (physical throttle range). The throttle plate in the carb deflects fuel in different places causing the front cylinders to run lean at WOT, and the rear cylinders to run lean at lower throttle settings (cruise).

    I have tried a lot of things to bring the EGT's back in closer. Some things helped, and I saw actual good results for power and efficiency. I won't get into all that here - as I never could get them close enough inline. My goal is to see EGT's at the very most 50 deg off, hopefully even closer than that?! 20-30 really should be doable. Maybe better with the superior atomization of the spray bar in the Rotec TBI, and of course a more equal intake manifold.

    Setup
    -1 40mm Rotec TBI (floatless, slide, spray bar carb) TBI-40-S
    -Custom 1 into 2 into 4 aluminum manifold placing the carb back slightly behind the engine (above and behind). The manifold will come up from the heads with 1.375" pipe (1.250 ID) about 5" tall so that the main larger pipes will clear the coolant tank. This of course is the major PITA part of the project. I can't tig aluminum very well, so bought the spool gun attachment for my 220v lincoln 180. I have used spool guns before and can do acceptable work. Nothing I'd enter into a beauty competition, but strong.

    *The Rotec has a built in regulator so no adjustments to the fuel system have to be made

    *It also has a feature to prevent fuel from leaking through the spray bar when the engine isn't running and flooding the intake or hydro locking the cylinders etc. if you forget (inevitable) to shut down the fuel system at some point.


    First step was to machine up the flanges to hook to the heads. I did those tonight. 5/16 6061 aluminum is what I used. I left the main holes that feed the heads a little small on purpose, I'll finish those by hand to make sure they line up with the heads nicely (no lip). The 1.375" alum tubes that feed it are a little larger ID than the factory manifolds on purpose. Since my tubes are longer, I didn't want to take a chance of choking off the engine at higher RPM. I will taper the .060 difference in the flange.





    Just been collecting parts other than this. Lots of different size and shape aluminum pipes, cones, couplers, clamps etc.


    I'll update this thread as progress is made, this project (hopefully upgrade!) will take a bit to complete, test, and hopefully put to work!
    S6S 116 w/VGs|MGL/FDS/AoA
    114hp zipper912|homebuilt headers/muffler/ram-air
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    Premium Member (Donated) scsirob's Avatar
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    You are having waaaaay too much fun!

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    Premium Member (Donated) WWhunter's Avatar
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    Gravity, I need you for my neighbor!! I am looking forward to your progress and reports!

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    Basic Member Denali's Avatar
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    @ GravityKnight :

    Amazing work on that Rotax. I heard through the grapevine that you are Austrian and that you used to work for Rotax? True?



    I am sure many forum readers would be interested in seeing what your shop looks like re the tools, drill presses, lathes, 3D Printers, etc. that makes these amazing projects possible. I keep seeing small lathes for sale, and your posts here makes it oh so tempting to start buying a few things like a quality drill press and a small metal lathe.

    Love your images. Please keep posting re the progress on your Rotax.

    Vielen Dank Tshuss...

    Grizzly small metal lathe
    Last edited by Denali; 12-05-2017 at 02:28 PM.
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    Premium Member (Donated) GravityKnight's Avatar
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    Quote Originally Posted by scsirob View Post
    You are having waaaaay too much fun!
    haha.... I dream up ideas that sound like fun in my head. Then I'm running that mill last night and it's 22 deg F in the shop and I'm telling myself I should not be allow to start anymore new projects for a long time!

    Quote Originally Posted by WWhunter View Post
    Gravity, I need you for my neighbor!! I am looking forward to your progress and reports!
    Thank you sir! Hopefully some good results, well.. result from this...


    Quote Originally Posted by Denali View Post
    @ GravityKnight :

    Amazing work on that Rotax. I heard through the grapevine that you are Austrian and that you used to work for Rotax? True?


    I am sure many forum readers would be interested in seeing what your shop looks like re the tools, drill presses, lathes, 3D Printers, etc. that makes these amazing projects possible. I keep seeing small lathes for sale, and your posts here makes it oh so tempting to start buying a few things like a quality drill press and a small metal lathe.

    Love your images. Please keep posting re the progress on your Rotax.

    Vielen Dank Tshuss...

    Grizzly small metal lathe
    Thanks Paul!

    Hey that's a good idea! I'll get some pictures of the shop. In the hanger I have mostly the basics for tools, with a few extras (welder, grinders, just one small vice etc.) Big projects have to be brought home. Thankfully, I'm only 3 or so miles from the airport. I would drag more equipment over there, but we are building a hanger at home and eventually will move everything closer.

    My garage at home has a little bit more to offer... drill press, car lift, bench grinder etc. Nothing too crazy, usually reserved for working on cars of course. The real magic happens at my Dad's shop. My folks live 1/2 mile away, in fact my home runway (1600ft usable) is in between my house and theirs. I have pretty free reign to use my Dad's shop as long as I'm not in his way, and clean up afterwards. Most of my work there happens in the evenings and weekends. He is pretty good about me going wild in there and has been patient over the years. He taught me to weld when I was 6 or 7? And so on... I think he rather have me around making a mess, than not around at all you know. I can run a mill and lathe etc. well enough to make the parts and mods I've done to the plane, and a lot of car stuff in years prior to this... but I am no where near the machinist he is. Most of the things I build don't require the absolute precision of the things I've seen him do. But now and then I make something pretty precise that even works when done!

    He is old school, we have a surface grinder that was built in the 20's I believe it was? All mechanical, noisy clanking back and forth.. I grew up in the shop and still love to hear it clacking around. I used to come up with reasons I needed to flatten something just to run that thing. His largest lathe is like 18ft long, has a chuck on it probably about 2.5ft tall. It's a monster. I'll get some pictures of these cool old tools. He is a genius in his field and I was lucky to be born into a family where I was brought up to believe everything should be done yourself - and we had most of the tools to do just that.
    S6S 116 w/VGs|MGL/FDS/AoA
    114hp zipper912|homebuilt headers/muffler/ram-air
    75"WW STOL|22x8.50mains/21x8.00nose/custom fork
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    Quote Originally Posted by GravityKnight View Post
    Thanks Paul!

    Hey that's a good idea! I'll get some pictures of the shop. In the hanger I have mostly the basics for tools, with a few extras (welder, grinders, just one small vice etc.) Big projects have to be brought home. Thankfully, I'm only 3 or so miles from the airport. I would drag more equipment over there, but we are building a hanger at home and eventually will move everything closer.

    My garage at home has a little bit more to offer... drill press, car lift, bench grinder etc. Nothing too crazy, usually reserved for working on cars of course. The real magic happens at my Dad's shop. My folks live 1/2 mile away, in fact my home runway (1600ft usable) is in between my house and theirs. I have pretty free reign to use my Dad's shop as long as I'm not in his way, and clean up afterwards. Most of my work there happens in the evenings and weekends. He is pretty good about me going wild in there and has been patient over the years. He taught me to weld when I was 6 or 7? And so on... I think he rather have me around making a mess, than not around at all you know. I can run a mill and lathe etc. well enough to make the parts and mods I've done to the plane, and a lot of car stuff in years prior to this... but I am no where near the machinist he is. Most of the things I build don't require the absolute precision of the things I've seen him do. But now and then I make something pretty precise that even works when done!

    He is old school, we have a surface grinder that was built in the 20's I believe it was? All mechanical, noisy clanking back and forth.. I grew up in the shop and still love to hear it clacking around. I used to come up with reasons I needed to flatten something just to run that thing. His largest lathe is like 18ft long, has a chuck on it probably about 2.5ft tall. It's a monster. I'll get some pictures of these cool old tools. He is a genius in his field and I was lucky to be born into a family where I was brought up to believe everything should be done yourself - and we had most of the tools to do just that.
    I grew up about the same and my dad still uses a bunch of old tools like a huge cast iron lumber mill table saw that the whole table tilts instead of the blade. However he's about a 6 hour drive away and still locks the shop up so I don't take his tools. Hahaha

    Maybe we need a new Thread just for shop tool pics

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    This is gona be a insteresting thread to follow!
    Is the standard 912 fuelpump good enough for the TBI?

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    Premium Member (Donated) GravityKnight's Avatar
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    Quote Originally Posted by Mitchell View Post
    I grew up about the same and my dad still uses a bunch of old tools like a huge cast iron lumber mill table saw that the whole table tilts instead of the blade. However he's about a 6 hour drive away and still locks the shop up so I don't take his tools. Hahaha

    Maybe we need a new Thread just for shop tool pics
    haha


    Is the standard 912 fuelpump good enough for the TBI?
    The injector requires anywhere from .5 to 12psi into the regulator. The pressure is regulated down to a real low pressure at the spray bar. The system relies on air running by the bar to pull vacuum on the backside (engine side) that is flat with the holes drilled in it, to draw fuel out. They work on gravity feed, so the rotax pump will work out good, and I'm leaving the electric pumps in the plane. Helps to fight vapor lock in the lines.
    S6S 116 w/VGs|MGL/FDS/AoA
    114hp zipper912|homebuilt headers/muffler/ram-air
    75"WW STOL|22x8.50mains/21x8.00nose/custom fork
    YouTube Channel

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    I still need to get some pictures of the shop for that thread..... I haven't forgotten .. completely!!


    Wanted to update this thread.

    My original plan was to start building all this jazz around Christmas time. I had a few extra days off and I was going to get after it. I had a Tacoma pickup for sale, and was going to take some of that money to buy the TBI unit when it sold. Surprisingly (they are good trucks, and popular here) it didn't sell until a couple days ago. A few weeks back I realized I wasn't going to be able to get a Rotec TBI from Australia here in time to work on it while I had a chunk of time to set aside. Meanwhile another plane was brewing in my brain. Which can be scary!

    I figured I'd give the Bing carbs/ Rotax manifolds one more try with some further modification. A couple weeks back I started some testing by making some extensions to move the carbs back 2.25" away from the manifolds. I wanted to see if more distance (time) for atomiztion would improve anything. It did help slightly with effeciency... but nothing too exciting. And the un even fuel distribution between cylinders was still very present. Next plan was to do some heavy modifications to the spare set of intake manifolds I have and really get creative!


    I modified them pretty heavily and installed a divider. In order to do that effectively in my mind, I needed to open up the mouth feeding the manifold so that there was plenty of flow available to each cylinder runner. I also wanted to be working with a round hole so I could divide it in half effectively. I cut the front of the manifold off, opened it up, and machined a ring and welded it on the front pretty heavily so I could then grind and open up the inside further. Then cut a slot and installed a divider right in the middle. Welded it up again. Then machined a tapered cone to go on the front of that. It was actually easier to machine up two of these and make them identical than I assumed it would be. Machined stuff like that is fun. Anyway, welded that on the front and cleaned it up. Also installed a 3/4" barb fitting welded on those cones for the crossover tube. After experimenting with a 1" crossover, and the large increase in main jet size needed, I decided to go a little smaller, I think 3/4" is the sweet spot for having plenty of volume to smooth out the engine, but not allow each bank to draw on both carbs so much reducing how much fuel is pulled from the main jet. This ended up being pretty accurate as it turns out.

    Anyway... here is the kicker... the divider manifold was a flop! I played with clocking the carbs and it didn't matter, EGT's were actually slightly WORSE from front to rear cylinders after doing this! Side to side they were within a couple degrees.. but at wide open throttle, I went from about 150-175 degree difference to over 200! RPM was down, power and efficiency both took a hit. I don't feel it flowed as well either - Overall RPM during climb and flat and level sucked. Damn!!! That was a LOT of work to end up worse off. Was pretty bummed... my big idea, well... didn't work worth a crap!

    Back to the drawing board it was. Figured, hell at this point, I'll just do some experimenting, until I have finally ruined those intake manifolds and have to put the other set on! After thinking it over, I decided to get rid of the dividers.... something told me that my opened up, enlarged, ported manifold might actually at least flow good, even if the fuel distribution isn't there... so I ground out those dividers and spent a few hours cleaning them up inside, porting them the way I think they should be, smoothing, blending etc.

    So what I ended up with, is a larger internally manifold in the area where it splits into the runners, and then that area smoothly tapers back down to the ID of the carbs and mates up to them nicely. This also places the carbs about 1/2" or so (have to measure again, I don't remember off hand what it was exactly) further back away from the manifolds.

    Anyway... I stuck them on there figuring it would be another blah waste of time result. And to my surprise, they work great! What!? Yea.... 50-60 degree at most difference at wide open throttle!!!! Cruise EGT's vary a little as you change the throttle plate position, but again, with real reasonable temps most of the time (0-50 depending on position). Power was up 130+ RPM's at the same altitude and temp! Thing is running strong again! Made a take off today in a nice crisp and cold headwind that was about 70ft lol.

    Now that things are so much more even, I was able to lean the snot out of it without any cylinders getting hot, and without it running rough due to some cylinders being leaner than others etc. Up this high, you can lean it pretty far without temp problems. I was cruising around at 8100 or 8300 or something like that today (I have a vid clip I'll upload) doing 104-105 MPH indicated, burning 4.0 GPH, and my plane is pretty draggy with not much prop pitch. Those are really good numbers. Before I would be around 100mph ish at that fuel burn. Pleasant surprise. Wide open it will go past 6000 rpms somewhere around 115-117mph indicated up high. I know when I was in Kansas a few months ago it would do 123-125 or so but was heading way to high RPM wise with only 17.1 or 17.2 degrees of pitch. A wild prediction is that at sea level, with a lot of pitch this thing would break 130mph no problem flat and level... but that is just a theory and I'd rather have it setup for take off and climb. Anyway, it was a long week of day after day, working on this, trying stuff, taking it apart, putting it back together, it was miserably cold. I was getting burned out, and thinking instead of relaxing while having some time off work, I have been going at this hour after hour, and not getting anywhere! It feels good to finally see some results and the best EGT spreads I have seen yet with this plane. There is no doubt in my mind, that if done right, the Rotec setup has the potential to run better with more power and efficiency... but I might save that project for the next plane, since I do plan to sell this one in a year to year and a half from now. If anything changes on that I'll report back. For now, I'm going to box up the countless pipes, materials, couplers, the flanges I machined etc. and save all that for a rainy day. I'm pretty happy with the bings (for once...for now). Thanks to anyone for reading!

    Couple pictures. I did not get any pictures of the final product without the dividers... I didn't expect them to work! But you can get the idea of the manifold modifications. Thanks,
    -Todd













    S6S 116 w/VGs|MGL/FDS/AoA
    114hp zipper912|homebuilt headers/muffler/ram-air
    75"WW STOL|22x8.50mains/21x8.00nose/custom fork
    YouTube Channel

  10. #10
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    Do you think this works the same with or without the Zipper?
    What do you use for leaning?
    Did you look into making a new manifold with equal individual runs to each port, a single carb and move the water tank?

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