Hot Air Pipe -- Necessary?

[bluejeepnut]

I have a '26 Touring with a Kingston NH carb. It doesn't have a hot air pipe installed. Should it have one? Do I need one?

Thank you

[speedytinc]

First. Uts either a kingston OR a holly nh.

Thats debatable. Some run one in the winter &/or humid climates & remove in the summer or not run in dry climates. The intake manifold can freeze up @ the elbow. If so you will probably notice a performance difference.
My conclusion is try with & without. I do notice icing where I am & run one.

[TXGOAT2]

In Iowa, I'd put the heat pipe on in October and leave it on until late April. It usually isn't needed in warmer weather, but if you often have cool, damp weather, it might be best to leave it on until Summer. When the engine is running, especially before it is fully warmed up, moisture can collect in the carburetor throat and intake manifold, which will interfere with idle and low speed performance. It's not uncommon for the moisture to freeze, regardless of the ambient temperature. The carburetor acts something like the expansion valve in an air conditioner, and the carburetor and intake can get far colder than the ambient temperature as a result. The heat pipe directs some heat from the hot exhaust manifold into the carburetor intake, which prevents moisture and frost buildup and helps the gasoline vaporize completely. The exhaust manifold gets hot much more quickly than the engine or the radiator. The intake manifold and carburetor can actually get much colder after the engine is first started.

[JBog]

It’s helpful in Wyoming!

[bluejeepnut]

Thanks guys -- this gives me the guidance needed to use the pipe as conditions require.

[Humblej]

I find it easier to just leave it on year round.

[1925 Touring]

I didnt have on on my T at first, I had a filter. I didn't have any real issues, but the intake would always get extremely cold and have mousture. I was heading to work one morning, a cool, foggy morning and the car suddenly began to run terribly in the middle of town. I thought I might have had an engine issue. That evening, I put my hot air pipe on, and it ran a LOT better. Never have run without it since. It keeps the intake nice and warm. It it seems to depend on the specific car, and driving conditions. I'm in Illinois, and weather varies, including humidity.

[Dan Hatch]

It is more about dew point than vaporization of fuel. Look up carburetor icing. Where I live we need them more in summer than any other time of year. Dan

Which makes me wonder, does a Holley straight through need one?

[Mike Silbert]

I leave it on all year round, it does not hurt driving in Maryland.
My favorite car tends to not like cold weather until it warms up.
Its a bone stock rebuild with Holly NH.
Even on the hottest days it will run faster than I should be driving it.

Heading for the 2024 MTFCI tour in Cadillac Michigan we left behind afternoon high temperatures of 100+ and woke up there to 40 degrees.
Had to go to the store and buy winter gloves and hats - In June!

Both MTFCA tours in 2026 are in northern areas and the MTFCI tour is in Canada
When you tour far from home you need to be prepared for anything.

If it didn't help, Henry would have been too cheap to install it.
My 2 cents
Mike

[Pep C Strebeck]

It is more about dew point than vaporization of fuel. Look up carburetor icing. Where I live we need them more in summer than any other time of year. Dan

Which makes me wonder, does a Holley straight through need one?

Northern Michigan in humid August, you need one, and that is running with a Straight Through NH. I agree with Dan, dew point/humidity more than anything else. Put it on, leave it on and be done with it.

[TRDxB2]

Your '26 Touring will let you know when to put it on

[TXGOAT2]

My car has no heat pipe. It does have an air filter. In dry weather, you'd never miss the heat pipe. When the humidity is way up, especially in cooler weather, the engine may exhibit "cold naturedness" for a couple of miles or so after startup. The relative humidity here can vary from very high to very low in a couple of hours or less. Temperatures can vary as much as 20 to 50 degrees F in an hour or so. At this moment, there is a 40 to 60% chance of rain or thunderstorms here and the temperature is 70F with high humidity. By 2 PM this afternoon, very low humidity, 20% or less, and 30 MPH winds are predicted with temperatures near 80F and blowing dust likely. Ideally, a manifold heat device would have a means to allow the driver to adjust it as conditions required, or an automatic adjustment like those found on more elaborate vehicles and most all modern vehicles.

[Loftfield]

No heater pipe on 1912 in North Carolina mountains. We have about 70 inches of rain per year,. so quite humid. Many years running a couple Model T's with no heater pipe. A post many years ago reported that dynamometer tests showed that heat pipes reduce HP by 10%. Since you don't have much HP to begin, the loss of ten percent might make a difference going up hills.

[TXGOAT2]

A heat pipe will not cause any noticeable power loss except in very hot weather, and the hot weather itself is a factor as well as the heat pipe. A heat pipe with a driver control would be best on a Model T, provided that the driver knew how and when to use it. In the 1920s, commercial gasoline was of rather low quality, with some of it being nearer kerosene than gasoline. Many automakers and aftermarket suppliers developed elaborate devices to offset cold starting problems and poor performance prior to full warm-up. The Ford heat pipe was a simple and effective way to get better performance from poor quality gasoline and prevent cold weather performance issues. The Vaporizer was a more complex device to better utilize poor quality gasoline and avoid cold weather issues. By around 1929, gasoline quality was improved by better refining procedures and many carmakers had adopted "hot spot" intake manifold assemblies. In the 1960s and 1970s, cars had elaborate automatic manifold and intake air and carburetor idle circuit heating systems along with automatic chokes. They worked very well when they worked right. The advent of fuel injection made most of that stuff obsolete, but I believe that idle circuit heat devices are still used on many F/I designs to prevent problems with frost.

[NealW]

A heat pipe will not cause any noticeable power loss except in very hot weather, and the hot weather itself is a factor as well as the heat pipe.

Not according to this dyno test with and without the hot air pipe!

https://www.mtfca.com/discus/messages/2 ... 1341900318

Some of the loss is due to the manifold heated air going into the engine, but the design of the hot air pipe itself, particularly on the earlier pipes, also greatly restricts the airflow. That doesn't help either.

After seeing these results, I haven't used the hot air pipe for several years. Granted, I don't drive if it is really cold, but I have not experienced running issues without the hot air pipe, and I don't want to lose that much horsepower for a device that was intended to better vaporize the poorer quality fuel of 100+ years ago.

I'm also a pilot with an airplane that has a carburetor. Depending on the temperature spread between the dew point and air temperature, you normally use "carb heat" (like you get with the T hot air pipe) when you throttle back to low power when in the pattern getting ready to land, but you don't want to leave it on all the time due to the power loss unless the dew point temperature difference is so small that ice can build up at any power setting.

[Steve Jelf]

Kingston NH?

[ewdysar]

A heat pipe will not cause any noticeable power loss except in very hot weather, and the hot weather itself is a factor as well as the heat pipe.

Not according to this dyno test with and without the hot air pipe!

https://www.mtfca.com/discus/messages/2 ... 1341900318

Some of the loss is likely due to the manifold heated air going into the engine, but the design of the hot air pipe itself, particularly on the earlier pipes, greatly restricts the airflow. That doesn't help either...

Gale Banks, Smokey Yunik and other famous racers have long expounded the benefits of more air density. Superchargers and turbos are the extreme answer, but cooler air has been proven over and over to produce more power. So hood scoops and cool air snorkels to get outside (ambient) air to the carburetor rather than the preheated air in the engine compartment have been used by racers, hot-rodders, and manufacturers alike for decades.

With all else staying equal, 100 deg air is 10% less dense than 50 deg air, which in turn, makes less power. We see the same thing from increases in altitude, less dense air = less power. The hot air pipe focuses even more heat into the incoming air, so the decrease in power is noticeable, even by just the seat of your pants. Mike Bender, Ralph Ricks and plenty of other heroes in this forum did the work and provided the objective proof that this is true, specifically for Ts.

All of that said, a hot air pipe can be useful today in the rare conditions that cause internal icing in the carb or manifold. And leaving one on continuously might not matter, if your typical driving doesn't exploit the full 20hp that your T engine should be able to produce. But for most of us, having one to install if the conditions warrant, could be justified. It's the T version of aviation carb heat, which every pilot knows should be used sparingly. For me, I'll take any small power improvement for my Ts, especially one that is as cheap and easy as not running a hot air pipe. If I ever experience carb icing in my T personally, I will revisit the issue then.

Keep crankin',
Eric

[TRDxB2]

Just an explanation of how icing occurs

When as a gas expands (air-fuel mixture) it causes its surroundings to get colder, hence the temperature in the intake manifold will decrease to what's called "latent heat of vaporization". The change in state (liquid to vapor) absorbs heat energy from the its surroundings (the intake air & manifold). This can cause the intake manifold can get cold enough to cause carburetor icing in cold or humid weather (need the moisture).
Same principle used in refrigeration, air conditioners, evaporation air conditioners and micro-fiber neck towels as the water evaporates.

As you already may know and/or experienced. cold air results in more dense air-fuel mixture than normal and a richer fuel mixture is needed.

[TXGOAT2]

Ideally, the heat pipe would be under the driver's control, like the choke, throttle, etc. Modern gasoline does not need the heat to vaporize under any but the most extreme conditions, but the heat is needed under some conditions to avoid moisture and frost problems caused by the refrigeration effect that occurs around the throttle plate and just downstream of it. If you drive in an area where conditions often cause problems due to lack of manifold heat, you might want to rig up a heat pipe with a driver control, or try putting a dime-size hole with a hinged shutter in a stock pipe to temper the incoming air.

[TXGOAT2]

The most practical solution for most situations where weather conditions vary widely:

OP: "Thanks guys -- this gives me the guidance needed to use the pipe as conditions require."

[Oldav8tor]

I live in Michigan. Plenty of moisture, wide range of temperatures. I do not use a heat pipe. I carry one under the back seat but "just in case" has never come up. I've installed a foam carb air filter, preferring to keep particulates out of the engine as much as possible. I lean the engine which results in it running a little warmer. The intake gets cool but I've never seen any frost. No problems over 13000 miles of driving my 1917 Touring.

Side note: Airplanes are provided with a control that lets you apply heated air to the carb if icing is suspected. In 50+ years and over 5000 hours flying I have detected significant carb ice maybe a half-dozen times or so, usually in less than perfect weather conditions. The only time it got serious enough where I had to leave the carb heat on continuously I was flying in clouds in the late winter, coming back from Florida. I picked up a little structural ice too and ended up landing in Tennessee and spending the night while the weather cleared. And yes, ducting heated air into the carb does reduce power.

[Allan]

In 60+ years of model T motoring in more than a dozen different cars I have never had the need to run a hot air device of any sort. Think southermn California climate.
Allan from down under.