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.

[TXGOAT2]

My car has no issues at ambient temperatures down to about 40F.... IF THE AIR IS DRY. If it's colder than that, I don't drive it, but I have driven other vehicles in all kinds of weather with no intake air heat equipment and the same effects are observed. A heat pipe, when conditions require it, can dramatically improve driveability during warm up. Under extreme conditions, a heat pipe might be needed full-time. Is the pipe attached to the manifold stud? If so, get a longer stud and use an extra nut or wing nut and spacer sleeve to secure the pipe. Then you could put it on or remove it in a couple of minutes as conditions demand. When it's needed, it's needed. When it's not, it's not.

[Oldav8tor]

Remember, one reason for a heat pipe was the poor quality gas "back in the day." The heat helps vaporize the fuel. That's not an issue today.

[TXGOAT2]

True. But condensate and frost remain a problem under conditions favorable to their formation. I know from experience that E-10 will not prevent condensation or icing. Higher blends might, but I doubt it.

[speedytinc]

It's nice to see Ford's view as documented in answer #50. Thanks for posting that.

My experience - Left coast.
I had a fresh motor. Took it out for test/tuning runs & I observed the following:
No heat pipe running a warm motor, The manifold iced up externally @ the bend, same as pictured above. From about 1/2 to full throttle, the motor ran rougher with intermittent missing. Back to the barn. Put the heat pipe on & retested. No more miss, but I did lose, maybe 8% of my top speed.

On my 14, I drilled 4 1/2" holes on the back side of the heat pipe. Was a good compromise. Some heat helped her run quite well. No visible frost.
I left the pipe on year round.

[TXGOAT2]

There ya go!

[Matt in California]

I have been doing winter driving at 40-60 degrees. I added the hot air pipe and made a short video:
https://youtu.be/3Y-bwJgEpos?si=5NiDepOqZRDrBidu

I am not sure I saw much improvement from the rough running.

What temperatures do you think Ford intended by “cold weather.”

Matt

[TXGOAT2]

Condensation and/or frost in the carburetor and intake manifold can be a problem under a wide range of weather conditions. There is no specific temperature or humidity level at which problems can or cannot occur. Where humidity is high, problems can occur with ambient temperatures in the 70s. Where humidity is very low, there may be no issues at any temperature when using modern gasoline. The best solution is a heat device with a manual control, which the driver could use when needed. Absent that, you may choose to use the Ford heat pipe during cooler seasons, and remove it in summer. But if you live in San Francisco, for instance, you'd do well to leave it in place all year.

[TXGOAT2]

I'd expect that driving in 40/60 F weather where any significant humidity is present would require the use of a heat pipe for quick warm-up, smooth idle, and optimum overall performance and gas mileage. Adding a heat pipe will not correct problems that are unrelated to manifold heat. If your car runs erratically with a heat pipe correctly installed, there is most likely some other issue besides manifold heat that needs attention. When using a heat pipe, the carburetor adjustment may need to be leaner than without one.

[Jerry VanOoteghem]

Here's what the answer to your question usually boils down to...

If the car runs better with it, it's necessary. If it doesn't run better, or runs worse, it's not necessary. Try it and see what happens.

[Matt in California]

Thanks for the advice as I showed in the video. I tried it. I will need to post a follow up video where I found more critical issue. But I will say that it did seem to run a lot worse in the thick fog that we have.

[TXGOAT2]

If you live where fog is a common occurrence, you need a heat pipe. Ideally, it would have a window or shutter with which you could regulate the amount of hot air directed to the carburetor.

[John kuehn]

I’ve always thought of the hot air pipe is the closest thing to an air cleaner. Yes I know what the purpose for it is but sucking dust and any thing else into any engine can’t be good unless there is some type of filter to keep it out. I guess Henry didn’t consider pulling in dust and dirt wasn’t that bad. Just my opinion

[John.Zibell]

I live in North Alabama and use this air filter. https://www.modeltford.com/item/CARB-FILT.aspx It seems to work fine and I don't experience carb icing even though it can get very humid. Maybe it picks up just enough heat from the hogs head to prevent extreme icing.

[TXGOAT2]

Ford used to consider about 10,000 miles to be the average life of pistons and rings. A T will run better, and far longer, with a good air filter installed, especially if you drive in dusty areas. Dust builds up hard, fused deposits in the combustion chambers and grinds away at pistons, rings, valve stems and guides, and cylinder walls. Some grit will find its way into the crankcase and increase wear on all moving parts. Dust particles will embed in the surface of babbitt bearings and cut away at the crankshaft. Ideally, a T would have a good air filter, and oil filter, and a driver-regulated intake air heat device. An air filter can dramatically reduce ring and cylinder wear. If you think city driving is dust free, try riding a motorcycle in traffic.

[TXGOAT2]

I use that same air filter. It catches a lot of dirt. My car has plenty of power, and I've driven it well over 15,000 miles with no indication of wear in pistons, rings, or bearings. I have not looked at the spark plugs in over 5,000 miles of driving, and there is no indication that they need any attention. Somewhere around 30% of my driving is on very dusty dirt roads.

[Daisy Mae]

I live in North Alabama and use this air filter. https://www.modeltford.com/item/CARB-FILT.aspx It seems to work fine and I don't experience carb icing even though it can get very humid. Maybe it picks up just enough heat from the hogs head to prevent extreme icing.

I've been considering that filter.
I have two issues. Living on the FL panhandle coast we not only have a lot of humidity in the summer, but also a lot of mist always generated off the surf that would suggest the need to retain the stove pipe.
Secondly, the sugar fine sand here is a constant risk always blowing across the beach side main drag. Not that I want to suck up that much abrasive.
A filter with icing risk trumps stove pipe / no icing but risks destroying internals in my mind.

[Scott_Conger]

There is zero doubt in my mind that an air filter will extend the life of an engine - my '13 is now going on 113 years still with its original engine and no filter, so imagine how much longer it would have gone WITH an air filter!

On the other hand, ask someone who had fuel run into the foam or paper filter while just sitting or while choking to get started, and then suffered a backfire how their day went.

Air filters work great until they don't.

A long lost poster here used to admonish everyone that a "T" that was properly wired never needed a fuse - and along that line of thinking, a properly carbureted car with an air filter doesn't need a fire extinguisher, either.

[TXGOAT2]

A Donaldson-type filter would be best. My next choice would be a paper element type. If I ran a car in coastal Florida, I'd insist on an air filter. A car run in areas where rain or snow is more common than not, or run exclusively on clean pavement, an air filter would be less critical. Where I live, road dust is a fact of life 90% of the time, and an air filter is necessary to avoid high wear rates. Frequent chassis oiling is also important to help flush grit out of working parts.

[Daisy Mae]

The sugar fine sand here is the biggest issue, it's in the air no less than the water mist. Ya T's survived fine without, but....I figure I need to protect the deep pocket investment of its rebuild. It's amazing how much sand I vacuum out of my F150's air box!
I run a wire mesh filter on Annie Elizabeth, my A, and she does NOT like it. I just tell her tough and lean her out.
As for fire extinguishers, I carry one in all my cars, antique or modern, something everyone should aspire to do like a good Scout!
Like everything it's just a balancing act of risks.

[TXGOAT2]

Cars that are driven on the road need an air filter.

[Steve Jelf]

With a habit of driving a lot of dirt/gravel country roads, it has been my custom for many years to run with an air filter in place of a pipe. Possibly because of where I've done that driving, the lack of a hot air pipe has never given me any trouble.

[TXGOAT2]

That's a very nice installation... and no significant fire hazard. If flooding were to be a problem, a small hole in the elbow at the lowest point would take care of that. Some updraft carburetors with breathers, such as used on the 8N Ford tractor, have a small hole in the carburetor air horn with a porous bronze plug to allow excess gasoline to escape.

[John kuehn]

My view is the same as using a transmission filter just under the access door to collect any debris in the engine. It’s a definite improvement in a T engine to have an air filter along with an oil filter.
For the historians among us when did Ford finally start using air filters for the engine air intake.
I know the early V8 did. So was that the earliest?

[TXGOAT2]

I don't think the Model A had an air filter as standard equipment. I don't know if Ford offered one as an accessory. I don't know about the B, but I'm pretty certain that all the V8s had one. Most other makes had air filters of some sort by around 1920 onward.

[Daisy Mae]

I know the A was not equipped.
My belief is Ford first introduced them with the introduction of the V8, but neither certain of that.

[John kuehn]

Here’s an early day photo I think I posted before. It’s the reason why an air filter may have helped to extend the life of a Model T engine. This was taken around 50 miles 100 years ago from where we now live. Think of the dust in those days and the tire punctures that T owners experienced on those roads and got use to it. And no triple AAA either I don’t think.

[Scott_Conger]

For at least the last 15 + years that I've participated in this Forum, these air filter conversations seem to occur about every 18 months or so. Some are more interesting than others. This one is pretty much middle of the road. The one thing that seems consistent, at least where pictures are involved, is that the majority of air filter proponents will not take even a rudimentary stab at protecting their carburetor with engine dust pans as supplied by the factory. So why is it important to take extraordinary precautions when the most basic original factory precautions are ignored?

When folks trot out the old "FORD expected you to re-ring the car at 10,000 miles" I have to chuckle because when these cars were new, the US was primarily rural and it was common for the earliest cars that they might not see 10,000 miles in their entire life. The plethora of folks new to "T"s and posting pictures of their original two-piece valves is testament to the fact that an enormous number of our cars survived intact for over 100 years despite not running air filters. For the cars that DID wear totally out, why is it always a single factor, i.e.: air filter which would have saved it. Could it not be the poor lubricating oil that carboned up into little black diamonds that cut every moving part be to blamed as well? Or the poor quality fuel that the factory admonished to "pour through cloth to remove dirt and sticks"? Wouldn't dirty or adulterated fuel cause wear? Or a myriad other contributing factors that ultimately wore these engines out. Blaming the lack of an air cleaner as the culprit would appear to be simply be building a case to support a predetermined conclusion.

I live in about as dry and dusty a place as there is...and I too, have to occasionally change a modern air filter in my car or truck that has collected dust/dirt - but I am following modern traffic at 55+ MPH with a forward facing intake, and have the pitted, chipped and cracked windshields to prove it. It's not enough that it is dry and dusty here, we put sand and gravel on the road instead of salt in the winter. It's such a joy to be passed by someone and have my car sandblasted and battered by rocks as they go by (but it beats a rusted hulk due to salt). On the other hand, My T sees no such speed, follows no other cars kicking up dust, wears its original dust pans, and has a carburetor which faces away from airflow. Do my "T"s suck in some dust? Of course. In the 15 years of driving them, have I ever noticed a deterioration of performance? No, I have not. Oil changes every 500 miles seems to do the trick in keeping things clean and in good condition.

So I say "knock yourself out" and do what seems smart to you - but at the end of the decade, my cars will more than likely still be running as well as any car sporting an air cleaner - and in most cases, with far more aged engines, to boot...and when that time does roll around, they may be running even better, since our carbs are not jetted or designed to run with the restriction an air cleaner provides.

Going sans filter isn't "right" and running a filter isn't "wrong", but if it takes a filter to allow one to sleep better at night, then do it. I on the other hand sleep just fine. It might be due to the fresh unfiltered air here.