Cold air coming into the carb is a heavier air and will pick up a greater amount of gas but does not atomize as well as hot air. Hot air is a thinner air, will pick up less gas, but will atomize the gasoline better.
So then does it make sense that we would have cold air enter the carb, pick up a greater amount of gas, then heat the air/fuel mix after the carb to better atomize the mix? wallaw! a super charged fuel mix. Yes?
Or are you getting tired of my stupid questions?
It is correct that cold air coming into the carburetor in heavier then warm air. The benefit of cold air is that is contains more oxygen not necessarily that it picks up more gas. The amount of gas picked up is determined by the carburetor adjustment and not necessarily the density of the air. Oxygen + fuel = energy.
Yes, the heating of the intake manifold after the carburetor helps and it is normal on more modern engines.
Thank you Jim. Good answer. I knew that when we have national drags here, the racers like the air temps to be cool rather then hot.
Perhaps if one were to drill the backside of the gooseneck and install a small electric heating element, maybe a magnesium strip or something, this could be done effectively and without detracting from the original look? The wire could be routed up and under the intake/exhaust manifolds and if you trimmed the gasket, around behind the backside edge of the valve cover to either the mag post or generator?
There were "combination" aftermarket manifolds made for the Model T that heated the air/fuel mixture after the carburetor by using the hot exhaust gasses to heat the intake manifold. I use the "economy" manifold on my '19 Touring with a Stromberg OF carburetor and the combination works really well. I have no idea if the insert to swirl the air/fuel mixture really works as I have never tried the unit with the insert removed.
The Simmons carbs had a heat coil behind the throttle plate. A small hole was drillled through the carb body for the power terminal and insulated. I've never seen one actually hooked up for use, so I'm not sure how they were wired. I've always assumed those were either wired to a switch for "as needed" heat use or maybe to the Mag for full time use?
If it is best performance you are after then anything you can do to isolate the intake from engine heat will be a boost to torque; and as a result, a boost in horsepower. Adding heat is not necessary at all with today's wonderful (for a Model T) gasoline.
In the era when the T was new it was necessary to heat the intake to make use of the wildly variable quality of available fuel. There was often very low RVP (Reid Vapor Pressure) fuel available, and in winter time it caused huge problems.
The Reid Vapor Pressure of modern gas is controlled by law, often varying monthly depending on what state or even county you live in. Your Model T running on 2011 gasoline does not need a heated intake at all.
Have you ever been flying a (carburetor equipped) Continental powered plane and watched the manifold pressure drop while penetrating cloud? Sure makes you hope the @#$% carb heat continues to work! I even saw lots of intake ice on fuel-injected Lycomings.
It's always interesting to lift the hood on the running T and see the ice collecting on the outside of the intake. You can only guess as to the shape of the restriction just downstream of the venturi.
I don't have a heat pipe on T'izzy, preferring to have an air filter in place. A soggy day is guaranteed to make her falter from time to time because of carb ice.
Having said that, I certainly don't dispute your statement concerning vapor pressure and heat isolation at all. But starting and running these engines are two separate evolutions!
Okay, I just happened to think of another issue. It seems that some people have occasional problems with ice and have to run a hot air pipe to keep things working as they should, while other people swear they have never had an issue and don't run one. I think part of the issue here may be driving habits. I have noticed icing as an issue on several Model T's around here over the years. There are a lot of ideal Model T roads in this part of the country with very little traffic. In many cases, we can drive quite a while without adjusting our throttle, or adjusting it very little. Now that I think about it, any case of icing I have had on cars with no hot air pipe have been when driving at steady speeds around 30mph and higher. The engine will start to miss & loose power and if you open the hood and look right away, you will see the telltale frosty spot at the bend in the intake manifold. Once the engine is off for a minute or two, the problem is gone and you can drive sometimes a couple miles before it happens again. Once the issue is identified, driving below the speed the icing happens at will remedy the issue until a hot air pipe is installed.
Now, the part I'm wondering about... What are the driving habits of the people that run stock 1909-1925 intake & exhaust manifolds and no hot air pipe that have never had an issue with icing? Also, what are the driving habits of those who have had icing problems and do run the hot air pipe?
Right now, I'm guessing that people who do not have icing problems may: live in dry areas and/or do a lot of driving at varied speeds. And maybe people who have encountered icing problems may: live in areas where constant speeds can be maintained for several miles at a time and/or relative humidity/dew point gets high in the warmer months?
Even if you have never had an issue, I have a suspicion that if you are the type that travels to various areas of the country for regional tours, etc. It may be a good idea to put a hot air pipe in your tool kit just in case you have an issue somewhere, someday.
The argument goes on. Our 13 T had a heat muff to heat the air going into the carburetor and our 13 Cadillac had a hot water jacket built into the carburetor. The carburetor is a Cadillac Carburetor and is about 14 inches long. A 1/4 inch diameter pipe is plumbed to put hot water in at the bottom and let it flow up hill to thermosyphon out at the top of the water jacket. It takes longer to heat the water than the air and the Caddy is slow to warm up because of it. The intake diameter of that 366 cubic inch four cylinder engine's carburetor is only one inch and it makes ice for quite a while until the water gets hot. I believe that the early REO's had the water jacketed carburetors too. Some good old boys use a coil of large diameter copper tubing filled with water from the engine wound around the intake manifold on their Speedsters rather than the heat muff.
Adam, I had a 24 that iced at idle with no stove pipe in Kansas on hot day, no hood sides. Put a pipe on and did away with icing. I also have a 25 with a pipe and does not ice. I don't drive either car enough to know if performance is different with or without pipe.
I went driving today at about 40 degrees OAT. Ran really good. No heat tube. I pulled the crank up twice with the choke on and key off. When I turned the key on it started by itself with no further touching of the crank (so - called "Compression Start").
Same thing on Christmas eve except it was about 35 degrees.
How does the Vaporizor Carb setup fit into this? Seems like a design solution but reports are performance is not as good as regular carb manifold.
I went on the Texas T Party with my '17 last year in East Texas. It has a Vaporizer, and not many cars can keep up with it. It runs fantastic. The Vaporizeer gets an undeserved bad reputation because not many people even attempt to use it. So, like many things, they think it is bad because it is somehow mysterious.
If any of you drive 1928-31 Model A's you know, Model A's do not have any sort of heated intake manifold.
The Model A might not have a heated intake manifold but the Zenith carburetors used on most Model A's are a touch better carburetor as far as vaporization than most Model T carburetors. Comparing apples and oranges here. At least that's my experience after owning and driving a Model A for 22 years. Also the design of the Model A intake is different than on the standard Model T.
What is this marvelous color you have painted your roadster Royce?! That is gorgeous!
Actually Dad painted it that color in 1951. Not the color I might have picked but it will always be that color as long as I own it.
On a stock Model A Ford, what is the flat on the side of the exhaust manifold with two threaded holes that the intake manifold bolts to used for? It sure looks like it is to transfer heat to the intake.
Maybe some heat transfers there; but in my opinion the more important function is to keep them together and aligned with the ports properly.
What a great car you have, Royce!
I had a '28 touring car with the vaporizer. Ran really smooth but was seriously anemic. We took it to the Christmas light display near Athens (that's in Texas, folks) one year. I had to get everybody else to bail out to get it to climb out of one of the creek bottoms on that trek. Embarrassing! I had gone through the lower end and replaced the pistons and valves which, of course, helped but she just never performed. I never explored far enough to find out why.
And that's only one of the reasons I wish I hadn't had to sell that car.