Temperature Balancing by Turning/Twisting the Carb
Posted: Sun Jun 11, 2017 2:09 pm
by MichaelFarley56
Greetings Everyone,
I know this subject has been discussed many times in the past, and it seems to be one of those eternally debated topics of conversation, but what the heck, I’m curious…
I’m curious to hear feedback and information from those who are flying behind an AeroCarb/AeroInjector and successfully was able to balance engine temps (EGT and/or CHT) by somehow offsetting the carb. We all know and understand the goal here; if we can somehow favor the mixture towards one intake side or the other, this may possibly help temps by promoting one side of the engine to run a little richer or leaner. The common method is to either twist or tilt the carb to favor fuel delivery towards one side of the intake system slightly. Easy in theory, but I’m curious who all has actually tried this.
If you’ve ever fiddled with carb orientation for this purpose, could you please reply and let us know what the issue was, what you specifically did to the carb, and how it worked out.
I do admit that I want to (probably) fiddle with mine a little bit; on mine, both the EGTs and CHTs tend to run coolest on the front-pilot side cylinder (#4 I believe) to the hottest being the rear, copilot side (#3). In general though, on my AeroVee the pilot side cylinders tend to run richer than the copilot side, so if there’s a solution such as a carb twist to help balance things out, I’d be happy and willing to try. But I hate to run into this blindly, hence the thread.
If anyone has any experience here, please share!
Thanks Everyone!
Mike
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Sun Jun 11, 2017 2:25 pm
by gammaxy
On my Aerovee, I rotated it about 15 degrees and didn’t notice any change, so I rotated it back to the initial orientation. My left cylinders also seem to run cooler than the right ones.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Sun Jun 11, 2017 7:17 pm
by MichaelFarley56
That’s interesting Chris. I know these engines aren’t fuel injected so they won’t be perfectly balanced, but I do run into CHT issues on high performance climbs. My right rear cylinder gets warm but it’s also the leanest so it would be nice to get that cylinder some more fuel at full throttle.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Sun Jun 11, 2017 8:34 pm
by fastj22
I think its more of an issue on the Jabiru. The intake is very close to the back two cylinders. So there isn’t much run to atomize. A small change in the orientation on mine can make big changes on how lean #6 and #5 in comparison. The forward four don’t seem to care. #6 is always my leanest on climb out. Its closest to the intake. Turbo guys shouldn’t matter a nit. And even aerovee with your long intake run.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Sun Jun 11, 2017 10:52 pm
by sonex892.
fastj22 wrote:I think its more of an issue on the Jabiru. The intake is very close to the back two cylinders. So there isn’t much run to atomize. A small change in the orientation on mine can make big changes on how lean #6 and #5 in comparison. The forward four don’t seem to care. #6 is always my leanest on climb out. Its closest to the intake. Turbo guys shouldn’t matter a nit. And even aerovee with your long intake run.
I realise this thread is about aerocarb. My experience is only with a bing on my 3300. When it comes to balancing the mixture by rotating the carb, I find that less rotation is actually more. When tuned so both left and right banks are reading pretty even. A matter of just a degree or 2, maybe even less, will spread the left vs right cruise EGTs by 50 degree C.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Sun Jun 11, 2017 11:52 pm
by jeff0196
My experience with the naturally aspirated AeroVee and cht and egt is the same as yours. The front run richer then the rears, and the left cooler then the right. My friend and I tried twisting the carb. First 15 degrees, no change, then 30, no change, then 90, no change, then 90 the other side to see if we could make it worse. No change. We gave up with moving it. I have a theory that fuel is dropped into the airstream in large slugs/droplets with the aeroinjector. When they make it to the intake manifold on the head, the inertia carries the heavier still liquid fuel drops to the front cylinders due to the design of the intakes. The left/ right balance must be more like pulses in the manifold and moving the injector one way or the other doesn’t seem to help. I think the both left then both right cylinder firing order contributes to this. The uneven running of this system was one of the biggest draws toward the turbo that in my opinion being a draw through turbo can make a homogeneous mixture under pressure that is much less sensitive to the effects of inertia and runs more evenly.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jun 12, 2017 12:04 pm
by sonex1374
I have a theory that fuel is dropped into the airstream in large slugs/droplets with the aeroinjector. When they make it to the intake manifold on the head, the inertia carries the heavier still liquid fuel drops to the front cylinders due to the design of the intakes.
This is exactly the conclusion I have come to as well. The intake design of the AeroVee is simple and compact, and has a lot going for it. However, getting perfect mixture distribution into the front/back cylinders is a bit harder because of this design. I have experimented with various means to better mix the fuel/air charge in the intake, but all the methods I tried were unpredictable and ultimately not worth keeping. I’ve often thought of continuing the experimentation with vanes installed in the intake runners to better split the intake flow to the front and rear cylinders, but haven’t done this yet. The turbo, however, is clearly the best mixture-homogenizer out there!
I have also experimented with twisting the carb, and I have also found that a few degrees one way or another will have an impact. However, if you are running overly-rich to begin with, you probably won’t notice the change (it will be obscured in the data). Try leaning to a very efficient mixture setting in flight and you should see the effect.
Jeff
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jun 12, 2017 10:00 pm
by rizzz
jeff0196 wrote:I have a theory that fuel is dropped into the airstream in large slugs/droplets with the aeroinjector. When they make it to the intake manifold on the head, the inertia carries the heavier still liquid fuel drops to the front cylinders due to the design of the intakes.
It’s a shame I only measure EGT’s on my rear cylinders (my MGL E1 only has 2 EGT inputs), as I believe the revmaster style intake manifold I have on my VW would fix this issue if your theory is correct. We would have some data to confirm it:
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jun 12, 2017 10:12 pm
by rizzz
And on that topic,
Here’s a recent learning I have to share, it may help others.
I recently did quite a bit of work on my engine including replacing the air filter on my AeroInjector.
When I went flying I noticed a serious imbalance in EGT’s left vs. right, well over 100 degrees C! The engine was also not running very well and I had to get the mixture setting just right to get it to run at all.
Obviously that flight wasn’t a very long one.
Comparing the data too older EGT data recorded during phase 1, it seemed EGT’s just went way lower than before on the left and way higher than usual on the right.
I had a serious mixture imbalance all of the sudden.
Because of all the work I had done on the engine it did not immediately come to me what the cause of this sudden problem was but to cut a long story short, it turned out to be the new air filter.
Once I replaced that again with another one all problems went away. Nothing looked obviously wrong with the bad one but I must admit I did not inspect it in detail, it must have had a tear or something which would perhaps “swirl” the air intake much more than usual and thus getting it pushed more towards one side than the other.
Anyway, this might be something to look at if you’re struggling with left/right EGT imbalance.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Tue Jun 13, 2017 2:01 pm
by Doron
It looks like the Jabiru main problem is the carburetor is very close the the manifold.
Is anyone ever try to extend the distance by adding a tube between the carburetor and the the manifold ?
Doron
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Tue Jun 13, 2017 9:26 pm
by vwglenn
Mike,
All VWs are notorious for the temp issue you describe. #3 is consistently the hottest cylinder in the cars for a multitude of reasons. It might be extremely difficult to beat that out of it.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jul 10, 2017 3:37 pm
by lutorm
Our AeroVee also has a very uneven mixture between front and back cylinders. I tested a redesigned (3d-printed!) intake elbow to see if it would alleviate the problem:
The short story is that avoiding the 90-degree turn helped even the mixture out some, but did not fix the problem entirely. I’ve written the experiment up here. It has EGT plots comparing the stock and custom intake.
Ultimately I think the solution is to run a separate intake runner for each cylinder, none of this tying together of cylinders (especially the ones on the same side that are firing unevenly.)
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jul 10, 2017 5:39 pm
by Fastcapy
I have similar intake elbows and it bumped up my rpms a bit (150ish static) and evened out the temps fairly well. With the rounded elbows and the Rotec TBI I have pretty consistent temps across the cylinders now and haven’t had problems with high CHTs like I did before the changes.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jul 10, 2017 7:24 pm
by MichaelFarley56
That’s a cool experiment! I can’t help but agree with you guys; I tried to accomplish the same thing by pulling the red 90 degree intake elbows and installing a set of Great Plains (had to modify them a little to fit) intake elbows. In fact, they look a lot like the 3D printed ones above.
They helped slightly, but just slightly overall. On my engine, the front two cylinders nearest the prop are certainly richer while the back two are leaner overall.
I also think there may be some limitations with the airflow through the cowling as well, at least on my engine. My back two cylinders nearest the flywheel have nearly identical EGT readings, but the pilot side cylinder (Sonex calls it #1; I call it #3) runs around 30 degrees cooler than the rear copilot side (Sonex calls it #3; I call it #4). If there’s a balance of mixture but a cylinder head difference, that almost has to be baffling/cooling air flow. I do have the top mounted oil cooler so maybe that’s blocking some air? I have played with some air dams in front of the cylinders a little to get more air to the back cylinders but haven’t had much luck there either. Oh well, it’s something to mess with!
Ultimately I also agree that a redesigned intake system with 4 equal length intake pipes, one to each cylinder, would help balance things. If someone wants to make me one, I’d be happy to try it out!! 
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jul 10, 2017 10:17 pm
by kevinh
Wow lutorm,
That is a great experiment (also a cool 3d print). I’m really curious about your future experiments!
Kevin
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jul 10, 2017 10:18 pm
by Bryan Cotton
Nicely done! Fun stuff!
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jul 10, 2017 10:19 pm
by lutorm
Yeah, it was fun!
Yeah, there’s clearly also something to do with cooling, apart from the mixture isuue. My assumption was that the difference in temperature between the left and right was due to the propeller rotation which would make the airflow go down towards the cylinders on the left side and up towards the top of the cowling on the right side. I don’t know how much difference that would make in flight, though, all my tests have been ground runs.
(It would be an interesting experiment to take pressure measurements inside the cowling, just above the left and right rear cylinders, and see if they differ. I’m also in the process of getting set up to measure cooling airflow in the spirit of http://www.n91cz.net/Pressure/PlenumPressure.pdf, but I was only planning on measuring the average upper plenum pressure.)
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Mon Jul 10, 2017 10:25 pm
by kevinh
FWIW - Even with a lycoming in my previous plane I spent plenty of quality time filing flashing off of heads and tweaking baffles to get the EGTs closer between the front and rear cylinders.
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Tue Jul 11, 2017 6:56 am
by peter anson
I think there is only so much you can do to even up temperatures. The photo below shows the internal passages of the Jabiru intake manifold. It’s really quite beautiful. They obviously went to lots of trouble trying to get even flow distribution, but my EGTs vary considerably, with a very noticeable difference between #5 and #6, the two outermost branches of the tree (top in the photo).
Peter
Re: Temperature Balancing by Turning/Twisting the Carb
Posted: Tue Jul 11, 2017 8:17 am
by DCASonex
For what its worth, my old Jabiru 3300 which had intake manifold with the single airfoil flow divider, tilting the carb very slightly did have the desired effect, also with that manifold, replacing the airfoil shaped flow divider with a plain 1/2" (12 mm) dia. round rod cut the EGT spread at WOT about in half but at a cost of slight increase in spread at cruise.
My new CAMit engine appears to have an intake manifold identical to later Jabiru ones, with two round rod flow dividers. That does seem to result in reduced EGT spread, but tilting the carb has little effect with this manifold.
Briefly tried the new manifold on old engine after some work on it, and seemed to behave same on both.
David A.
Now, opening the throttle you have to be more careful, precisely because if you do it too fast you’ll get a lean stumble and the engine won’t respond.
