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Old 05-07-2008, 10:16 AM   #1
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Window screen vaporizer

I worked on a contract in North Dakota in the early 70's when there was a gas shortage and stations were limiting the amount you could buy.

Several of the old timers there said that during the depression they put a piece of copper window screen sandwiched between two gaskets under the carburetor to help vaporize raw gas droplets.

They said however, that the screen had to be replaced occasionally because a hole would be eaten in the center of the screen after some period of use. The fact that the copper is consumed tells me that at least something is going on in there. Today we have aluminum or fiberglass window screen, and copper is hard to find.

I tried this recently, and it seemed to help. There are no hard figures yet. Here is one thing to watch for: on my Holley, the throttle plates extend below the bottom of the carb when they open and cut the screen in a half-moon shape. A spacer would be required.

There may be a slight reduction in performance since it does in effect reduce the bore area.

Anyhow, here it is. maybe it is a forgotten piece of science, or maybe just country lore, but it does make some sense in theory.
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Old 05-07-2008, 10:43 AM   #2
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Copper is a catalyst for several hydrocarbon reactions... but it's likely it just oxidised, since catalysts by definition are not consumed...

The carb screen theory in general is that it helps break up the larger fuel droplets, making for more efficient atomisation. Stainless steel screen has come to be preferred for this, as aluminum oxidises readily and breaks up, possibly entering the engine.

The most efficient arrangement is claimed to be a cone shape, or orienting the screen at an angle...

My suggestion therefore is to look for sieves/sifters in the dollar store made from stainless steel mesh. There should be enough angle on the sides to give some of the claimed benefits of the cone, and it's a cheap way to find stainless steel mesh. Plus the shape may help the throttle plate clearance issues.

On the copper front, one of the reactions it mediates at temperatures around 100C is the thermolytic cracking of ethanol into H2, and butyl acetate, so a copper screen inside a heated manifold with hot air induction may crack ethanol in gas down into H2.

I am pondering copper plating my intake ports to take advantage of this on a MPFI motor.
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Old 05-07-2008, 11:37 AM   #3
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I did some research, and found this on another forum:

http://www.mpgresearch.com/forum/vie...a&hilit=screen

Most interesting was the claim that two layers of mesh produced FAR smaller droplets. Also, with a single screen some claim no increase in gas mileage.

Depending on where you look, there are claims of anywhere from 10% to almost 50% reduction in fuel consumption.

So I am off to town to search for suitable mesh to give it another try.
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Old 05-07-2008, 03:15 PM   #4
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http://www.maryngroup.com/Archives/A...ackhomemag.htm
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Old 05-09-2008, 12:05 PM   #5
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After some research I found that droplet diffusion screens are not that uncommon today. Some find nice increases in mileage.

But there are problems. An aluminum screen may last two weeks, galvanized iron a few months. Stainless steel in better, but may be a disaster if sucked into the engine.

I am testing my version now. It has a single layer of pantyhose material pulled tight on the upper side of the lower EGR valve gasket, and a looser one glued to the lower side. The idea is the lower one will be pulled more or less cone shaped by the airflow.

Only 10 miles on it so far, but it shows that the material will indeed withstand the forces involved. I light and mirror allow me to examine the fabric by looking down the intake. Lower and mid throttle is smooth and idle is improved. Open throttle has suffered some.

As we know, not all cars respond the same to modifications. This may give me some idea if this is worth pursuing on this car. I have serious doubts it will survive a backfire.
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Old 05-09-2008, 12:11 PM   #6
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Gut feeling here is not to try acetone/xylene or any other solvent additives with the pantyhose, or you might be cleaning globs of sticky crap out of the intake for weeks.
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Old 05-09-2008, 12:16 PM   #7
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Interesting about the double mesh. I theorise that what happens is that droplets split on hitting a mesh wire, but leave fuel behind, after a few hits in the same area, this builds up enough to be a drop that will be sucked off by the airflow... BUT, if you have another layer of mesh, it webs between the sets of wires by capillary action and is dragged off in finer droplet or vapor form, due to offering more surface area to airflow than if it just tried to form the minimum surface area shape around a single wire.
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Old 05-09-2008, 05:48 PM   #8
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I tried that on an old Chrysler Newport I had about 20 years ago with a fine brass screen. I had trouble with the thing icing up on cool humid mornings.It was annoying enough that I took it out before I got a full tank of fuel through it to check the mileage.With some warm air in the intake stream it might work better,I just had an open element round air cleaner on a Carter A.F.B.
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Old 05-09-2008, 05:49 PM   #9
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Quote:
Originally Posted by RoadWarrior View Post
Interesting about the double mesh. I theorise that what happens is that droplets split on hitting a mesh wire, but leave fuel behind, after a few hits in the same area, this builds up enough to be a drop that will be sucked off by the airflow... BUT, if you have another layer of mesh, it webs between the sets of wires by capillary action and is dragged off in finer droplet or vapor form, due to offering more surface area to airflow than if it just tried to form the minimum surface area shape around a single wire.
I think there's enough airflow, even at idle, to keep this from being any more of a problem than puddling without any restriction. I don't know about a port-injected car but my TBI truck I'm sure would benefit from it.
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Old 05-09-2008, 08:19 PM   #10
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This was an interesting and inexpensive experiment, but has not worked for me. Using the same "test path" I got 9.04 MPG without the air conditioner on. Previous test was 12.96 MPG with the air conditioner on. The pantyhose filters will be removed.
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