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Wed Dec 07, 2016 1:31 pm

I have been thinking a lot about all the progressive carbs out there that run kinda crappy because the manifold is not heated. Just wondering if something like 4 of these at say the 2 amp versions, or something like it might not work to heat the runners so the carb runs better. 4 x 2+ amps is about 10 amps. It is a lot for someone already running a lot of equipment but one could put a switch on them to switch off when running at night with headlights and fogs on.

something like:

http://www.annodindustries.com/shop/drain-pipe-heaters

Wed Dec 07, 2016 1:38 pm

I suspect that would be like a fart in a windstorm, they are designed to keep a plastic drain pipe slightly above freezing, the BTU's a large volume of fast flowing air with gas evaporating in it generates (or pulls) would overwhelm it I think.

Wed Dec 07, 2016 1:42 pm

I tried something like that years ago on my 1300 bug engine, Wrapped heat element wire around the manifold just below the carburetor. Couldn't tell it did much though. It was icing. Eventually burned out the generator.

Wed Dec 07, 2016 2:57 pm

I thought about something similar Steve but using "heat tape". I have to believe that Mark is right about the flow being too high. Warm air down the carb throat works too and I confirmed that on my test stand. Either down the throat or onto the runners themselves. Kinda reminds me of flying a Cessna on short final. I believe that's how Wildthings solved the problem.

Wed Dec 07, 2016 4:19 pm

aeromech wrote: I thought about something similar Steve but using "heat tape". I have to believe that Mark is right about the flow being too high. Warm air down the carb throat works too and I confirmed that on my test stand. Either down the throat or onto the runners themselves. Kinda reminds me of flying a Cessna on short final. I believe that's how Wildthings solved the problem.

Thought about the heated air, I had a carb heat stick open on Jacumba grade in 1985 on my CJ7 and set the inside of the manifold on fire, melted the intake and carb in the 20 seconds or so the torch was lit. That is the only reason I was kinda steering away from that solution. The flap stuck in the open position and the heat set the plastic on the preheat tube on fire which ignited the spray in the carb and manifold....

Wed Dec 07, 2016 4:40 pm

Wow, although we can pick up warm air from under the heads at a fairly consistant temperature so odds are it'll never get hot enough to start a plastic fire like a stove on an exhaust manifold may.

The only way I can think of to get enough BTU's on the runners economically is small exhaust tubes brazed to the bottoms in a similar way to a type 1 manifold, like that industrial motor Wildthings had. To do it electrically would require a second alternator at the very least, and oil doesn't always get hot enough so bypassing the cooler to similar pipes attached to the runners may not get warm when you need it or overcool the oil.

Myself I've given up trying to reinvent the wheel, VW already did all the R&D and went with dual carbs or FI. I like the Weber progressive, it's a really great carb and very tuneable, but it only works well on heated short manifolds like you find on watercooled cars.

Thu Dec 08, 2016 7:08 am

busdaddy wrote: Wow, although we can pick up warm air from under the heads at a fairly consistant temperature so odds are it'll never get hot enough to start a plastic fire like a stove on an exhaust manifold may.

Isn't this how VW did it in 72-74 with dual carbs? route warm air heated by the passenger side heads up through the firewall and into the air filter? Seems a simple solution to get gently heated air.

Some motorcycles and some air-cooled small aircraft engines do use electrically heated carbs to prevent icing so that's not a crazy idea either. I suspect it wouldn't be enough to keep the runners themselves from icing/condensing, but only real way to tell is to try it.

http://www.aircraftgraphix.com/jabiru%20carb%20heat.htm

Thu Dec 08, 2016 7:22 am

VW used two carbs mounted on short manifolds and never used a single center mounted carb probably due to the icing troubles.
I fought it on my 72 when it was cold so I had long warmups before driving.

Thu Dec 08, 2016 8:09 am

all of you are certainly correct. I was just thinking about it because there are so many folks here who have gone the progressive route thinking it was a lay down deal. I am sure it could be done with plumbing but that sure doesn't seem like a simple solution with so many different kinds of exhausts. I was just wondering if the electric heat from a strip might be better than nothing. The 2.5 amp ones X 4 would have been 10 amps which with the headlights off is doable on a 55 amp alternator. The center of my CJ7 manifold had a heater under it that came on when the car first started cold. That was enough to heat the fuel - however it had little fingers that stuck up into the airstream to be sure all the heat went into the air and fuel. Basically it stopped fuel puddling under the carb when cold.

Thu Dec 08, 2016 11:26 am

WhirledTraveller wrote:
Isn't this how VW did it in 72-74 with dual carbs? route warm air heated by the passenger side heads up through the firewall and into the air filter? Seems a simple solution to get gently heated air.

If you look at Volkswagen's engineering with any of their carbureted engines, you will see two completely parallel systems at work.

a) preheated intake air (mostly to control water condensation/frosting)
b) manifold heat (mostly to control gasoline condensation)

a) preheated air is designed to switch off around 60* on the thermostatically controlled systems
b) manifold heat never does shut down

ergo!
a) there is little condensation or carburetor icing above 60* in the intake air itself
b) but large metal heat-sinks like manifold pipes need to be warmed more substantially because downstream of the carburetor, a fuel/air vapor will readily condense out of the intake air onto the walls of the pipes.
The heat provided by exhaust flow through the heat riser is pretty substantial, and it needs to be hot to keep the passage clear.

The intake manifolds on the factory dual carbs are cast iron for a reason, they draw heat from the heads nicely and maintain a steady heat-sink.

Latent heat of evaporation seems to be about 20-30* below ambient, so don't think you can't get condensation on a 80* day.
Colin

Thu Dec 08, 2016 11:43 am

Going back to electrical solutions: What is you were to use something like a boat battery (a large battery made to be drawn down over and over) then us something like what the OP was suggesting. And since you have a whole battery designated to heating your manifold during the winter warm-up period, if needed you could increase heat there and even pre-heat before start up. As well as you could turn it off once the motor is going with either a sensor near top of the intake manifold. This would allow you to charge the battery just like you would any other secondary battery, shouldn't be too much of a strain on the generator/alternator (whichever the OP has)

Although if you have a warm intake manifold with cold air running through it, you may end up with essentially condensation on the intake manifold and be running water through your engine. Not like it isn't happening already during humid times though I suppose.

Thu Dec 08, 2016 1:18 pm

But manifold heat isn't just for warmup or winter, it needs to be hot all the time when running, even on a warm summer day. Cooling air comes in over the top of the engine and also cools those manifold runners whether it's warmed up or not.

Thu Dec 08, 2016 1:38 pm

we didn't run manifold heat on the race cars but they get hot enough under the hood to burn the paint off on the motor above the headers etc. I was hoping for an easy solution without folks having to weld and run piper everywhere. Many of these folks have trouble adjusting the idle screws so something significant is not a viable solution I think. maybe just build some simple aluminum tunnels that cover both runners on each side and plumb part of the heat exchanger heat to them with an aluminum tube fitted onto the heat exchanger risers. Maybe add a small siphon Y and venturi to bring in ambient air to semi-cool the air a little.

Thu Dec 08, 2016 2:00 pm

busdaddy wrote: But manifold heat isn't just for warmup or winter, it needs to be hot all the time when running, even on a warm summer day. Cooling air comes in over the top of the engine and also cools those manifold runners whether it's warmed up or not.
Plus there is the latent heat of evaporation in taking liquid gas and vaporizing it, which is the carburetor's job. As the gas goes from liquid to vapor form, it absorbs heat, which is why the carb gets cold, and the intake manifolds, too. (Also happens if you use aerosol "canned air" -- you can feel the can getting cold.) Somehow, this cooling effect has to get overcome. And busdaddy is right -- it is there constantly, which is why carbs "ice up".

Fun fact: This effect is so powerful that the ancient Egyptians used it to make ice, in the desert. If you put out a thin pan of water in the dry desert night air, it will lose so much heat due to this effect that a thin layer of ice will form on the surface.

Thu Dec 08, 2016 2:30 pm

I built this for a friend of mine last summer who's manifold runners were sweating worse than a whore in church..I didn't invent this as I'm sure you all have seen something similar to this before..but it did help a lot, especially on hot and humid days..
It didn't totally fix the icing problem, but it could be something professionally engineered ( not by me haha) and sold to the masses..
Personally, I think the progressive is a waste of $$ on the aircooled engine and will always recommend duals..

Thu Dec 08, 2016 3:26 pm

fes - where are you pulling the warm air from?

Thu Dec 08, 2016 3:35 pm

The fresh air heater hose goes through the hole in the the engine tin on the 3/4 side with a fitting and sits just above the number 4 exhaust manifold by the head..

Thu Dec 08, 2016 3:42 pm

you drilled a hole and installed a fitting above the cylinders? The reason I ask is there is an inlet into the heat exchanger where #4 is. That is where air is pushed into the exchanger on late bays when the boost/defrost fan is on.

Thu Dec 08, 2016 3:51 pm

Use a late heat exchanger dump on the driver side. Run it into a silicone hose thru the driver battery tray and into a plenum made of bent aluminum that lays over the runners on both sides. If the heat is too much use an aluminum can about the same size as the hose in the hose and put different size holes in it to get different flows. At some flow the heat should be about right. The plenum can as simple or sophisticated as one wants. This should be able to provide enough heat to keep the runners warm under any circumstances.

Thu Dec 08, 2016 3:52 pm

SGKent wrote: you drilled a hole and installed a fitting above the cylinders? The reason I ask is there is an inlet into the heat exchanger where #4 is. That is where air is pushed into the exchanger on late bays when the boost/defrost fan is on.

Nope.. no holes drilled, used the existing heater booster fan inlet..( if we're talking about the same thing here) it's about the size of the holes in the rear engine tin of a type1..found a fitting in the electrical conduit section of the hardware store that fit almost perfect..screwed in and sealed with aluminum duct work tape.