balance tube

by bill martin in General Tech Discussion 11 years ago

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Re: balance tube

by bill martin » 11 years ago

bill martin

10 757 0

Alan,

I used 6061-T6 grade aluminum. It is about the most commonly available aircraft grade and is what I had lying around the shop. Easily weldable.

I don't really inderstand why Gregs' application didn't work unless, as he said, the side location of the tube caused an airflow problem.

If you have the room to do it, the method I used would allow you to remove the whole thing if it doesn't work. Mine is still working smoothly and I have removed the factory balance tube entirely. Just screwed brass NPT pipe plugs into the manifold where the tube fittings were mounted. In retrospect, The only thing I might have done differently was to use 1" ID tubing instead of 1 1/2". That would have allowed me to use a 1 1/2" block to make the manifold extension rather than a 2" block. It would also more closely match the FLYGAS model.

Using the manifold extension also gives one other benefit. If you are old enough to remember when Chrysler came out with the Ram Charger system in the fifties, all they did was extend the manifold to carb tubes. The carb on the left side fed the manifold on the right side and vice versa. This gave the fuel air mix more space to ram itself into while the valves on a given side were closed. It was that simple and it worked. With that idea in mind, even extending the manifold a couple of inches without changing the balance tube should give some improved performance.

If you do remove the existing balance tube, you will have mount your fuel hose distribution manifold a little differently. Also make a different attachment point for the carb support spring. Both are easily done and I can post pictures of mine if you like.

As I cautioned before, this mod does not increase horsepower or top end performance enough to measure. Since I cruise at around 41-4200RPM it did smooth out my engine considerably and did improve fuel consumption. I do disagree with FLYGAS on one point. They say that balancing the carbs is not as important with the large tube. The large tube will balance manifold pressure much better but it will not balance fuel/air mixture ratios. Carbs still have to be balanced.

Any way I can help, just let me know. Good luck.

Bill.

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Re: balance tube

by bill martin » 11 years ago

bill martin

10 757 0

Alan,

Let me correct one misstatement. Fuel/air ratios remain the same regardless of how far open or closed the carb butterfles are. You get more or less of the mixture but the mixture remains the same. With that in mind the carb balance is not as critical as with a small balance tube. Balance should still be done however. The better the carbs are balanced, the less critical the balance tube becomes.

Bill.

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Re: balance tube

by Alan Arnold » 11 years ago

Alan Arnold

20 188 145

Bill,

Thanks for the info. Yes, I remember the cross plane manifold. It sure looked radical and still does. Also there are several "performance" products on the market, really nothing more than manifold extensions to be mounted under carbs or throttle bodies that promise "more power".

Like you, I'm not looking for more power per se. I like the smoother idle and less requirement for perfect, exact, carb balancing for the entire RPM range.

I just need to gather materials, including shorter air filters.

I'll post progress as it happens. Don't get in a hurry for it though. Honey dos.

Alan

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Re: balance tube

by Alan Arnold » 10 years ago

Alan Arnold

20 188 145

Hey Bill.

I have been working on this mod for a couple weeks now and it is flying. See the pictures below. I made the blocks out of 6061 2" billet (plate?) and 1"ID x 1/8"wall 6061 tubing from onlinemetals.com. A friend welded it for me. The weight savings from grinding the block smooth as you did wasn't worth the effort for me as I don't have a table mount belt sander. Thus the "faceted" look. I couldn't find any short radius aluminum 90 deg bends so I was forced to use 1"ID thin wall copper pipe and solder it together. It is coupled to the aluminum tubing with 1-3/8" fuel/ethanol tolerant hose with a small space between the two tubes for vibration isolation. This is installed in a Highlander with not much room above the engine but there is no contact with the cowling. The 1-1/2" through-hole is very smooth (whew!) and the balance pipe is flush and rounded on all interior edges, at the through-hole and at the soldered 90's.

The engine runs very smooth at almost every power setting except full throttle. With the last 1/4" of throttle the engine starts to "miss". It feels like a lean miss, but it might be a rich miss. It is also running about 200rpm less at full throttle than before. That is mystery number one. Mystery number two is when I pull the throttle back that 1/4" the 200rpms come back instantly and now it runs at the same rpm, 5200, as it used to at WOT. This is static and climb rpm.

I couldn't stay and work on it any more yesterday, but the next time I go out to the airport I'll do a static run for a minute or so and then do a quick shutdown and pull a plug for a read.

Does anyone have any thoughts about the miss? Bill, Roger, Mark? Anybody?

I'll let you know how the plug read goes.

Alan

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Re: balance tube

by bill martin » 10 years ago

bill martin

10 757 0

Alan,

Good looking installation.

As for the throttle anomaly, I had exactly the same problem. My engine was originally set up for full throttle at 5500 RPM. After installing the new balance tube, I would reach 5500 RPM at about 95% throttle. If I went further with the throttle, the engine would begin to miss. I just adjusted the stops on my quadrant so that it wouldn't go past that 95% point.

My thoughts are this:

My prop pitch was set to use all available horsepower (100% throttle) to reach 5500 RPM. After the tube change, the engine was still using all available horsepower to reach 5500 RPM. the difference being that it was reaching the horsepower limit at a lower throttle setting (95%) due to better airflow. Not being an engineer, I don't really understand why the miss once you reach full available HP and continue to open the throttle but adjusting the throttle stop cured it.

The larger tube does not increase HP. The more you open the throttle, the less effect the tube is. It is strictly for better performance at low throttle settings. I cruise at around 4100 RPM and idle at about 1600. My throttle response is perfect between idle and 5500 RPMs. No hesitations, flat spots, or misses throttling up or down. Just did an annual last month and the plugs are a beautiful tan and all temps are well within specs.

If I could cruise my engine at 5000 or 5200 RPM as the factory suggests, I probably wouldn't have bothered with the tube change. For my constant low end operation though, the tube has been a real improvement. Definite improvement in smoothness, especially at idle.

If you figure anything out on the top end miss, let me know.

Bill.

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