How much HP will the thermosiphon handle?

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How much HP will the thermosiphon handle?

Post by ewdysar » Thu Oct 21, 2021 3:30 am

We all know that a well working Ford thermosiphon system will easily dissipate the heat from a stock 20hp T engine. Switching to a new flat tube radiator adds cooling capability that can handle most flathead upgrades like a performance cam, carb, and higher compression, which typically work out to be 30hp or less. Once you get to a overhead valve set-up and the engine can generate 40hp or more, at what point is a water pump or other significant cooling upgrades needed to keep up with the extra heat?

I believe that most Rajo, Fronty, and Gemsa equipped engines have/had waterpumps.

Eric


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 21, 2021 3:52 am

Duty cycle would have a lot to do with that ... how much of the time is the engine running in the higher speed/power ranges? Vehicle weight, rolling resistance, and aerodynamic drag are all factors to consider. Another thing to consider is that an OHV setup will dump less heat into the water jacket than will a side valve setup, all else being equal. Aluminum pistons will help dissipate combustion heat to the oil. Adding an outside oiler or oil pump system will help cool the oil. Ambient operating conditions are another factor to consider. It's worth noting that a number of farm tractors ran very successfully without water pumps. Using modern coolant blends can enhance the performance of thermosyphon cooling systems. The Model A Ford engines had water pumps of a crude sort, and developed about twice the specific output of the Model T in a car that weighed about 25 to 30% more. The Model A system is a a hybrid thermosyphon/pump system that relies as much or more on the thermosyphon principle as it does on the small and poorly-located pump.


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Re: How much HP will the thermosiphon handle?

Post by Wayne Sheldon » Thu Oct 21, 2021 5:15 am

It really isn't a question of thermosyphon versus a water pump. The beauty of thermosyphon is that the more power from the engine? As long as the radiator can handle the heat dissipation, ambient temperatures etc, the faster the thermosyphon will move the water! The limiting factor really is the radiator. Brass era radiators are the smallest. 1917 through 1923 low radiators are better, but still a bit small. The 1924 through 1927 full thickness core radiators are the best for heat dissipation. And as you mentioned, the newer flat tube cores also help.
Honeycomb type radiators can be either better of worse depending upon specific designs and water capacity of the cells. Honeycomb radiators are also much more prone to passage blocking within the cell structures due to rust or hard water. They can be very difficult to clean out if they have been badly plugged.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 21, 2021 10:08 am

Radiator frontal area is limited in T. Racers developed the V-type radiator to address this issue.

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Re: How much HP will the thermosiphon handle?

Post by TRDxB2 » Thu Oct 21, 2021 10:56 am

To properly answer your question if would be helpful to know how much heat your modified engine would be generating in order to ensure that your cooling system (water & oil systems) would effectively maintain a proper operating engine temperature. Most documentation suggest a range between 180 -210 °F. To simplify the thermosiphoning in a Model T, think of maintaining a temperature differential for the system to work. Anti-freeze/coolants are used to keep the coolant from freezing and/or to raise the boiling point of the coolant, but don't have a direct effect on keeping the coolant in the proper operating range - that is the job of the water & oil cooling systems.
Several older discussions have noted that their water cooling system were working properly when there was between a 30-90 °F temperature difference between the coolant entering the radiator and that exiting https://mtfca.com/phpBB3/viewtopic.php?t=4644. The cooling capacity of a radiator is dependent one many factors - air flow through it being a major contributor. You might consider an electric fan...
So the answer to your question depends on how well your cooling system is designed to can keep engine temperatures in range. A water pump isn't always an answer either, if the system can't cool the fluid it would just be passing the hot coolant.
Note: To cold coolant into a hot engine isn't good either.
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Re: How much HP will the thermosiphon handle?

Post by Norman Kling » Thu Oct 21, 2021 12:05 pm

The most important things with a thermosyphon system are (of course) the condition of the radiator and block. Next would be the amount of wind passing through the radiator. this depends on the fan when idling when parked or slow speed or the wind going through the radiator at higher speeds. That is why many T's regardless of the horsepower of the engine will overheat if left idling for a long time or when driving in parades. However the same car will run at normal temperature at cruising speeds or even uphill.
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Re: How much HP will the thermosiphon handle?

Post by John Codman » Thu Oct 21, 2021 1:12 pm

Another thing to remember is that an OHV setup (for example) only will dump more heat into the cooling/oiling systems when the engine is producing more power (then 20 hp). If you are spending 90% of your driving time in pretty much the same speed range as a stock Model T, then I see no problem. If you are asking the engine to produce more then it's stock horsepower for an extended period of time, such as climbing a long hill, there will be heat generated in excess of what the cooling system was designed to dissipate. My Berg's flat tube works fine under all conditions here in sunny SW Florida. I think that it could easily handle another 10 hp for extended periods of time, but I would keep any use of power in excess of that to a relatively short duration. I am assuming that you will have a modern flat-tube radiator in excellent conditions installed.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 21, 2021 2:10 pm

LESS HEAT, NOT MORE. OHV heads typically expose less combustion chamber surface to the combustion heat, and exhaust valve seat cooling is often better than a typical side valve.

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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Thu Oct 21, 2021 2:27 pm

Ok. So the consensus of the performance model T engine builders/owners like Hank, Les, Clayton, Bender, and others is that they don’t use water pumps for high output OHV T engines? Or do they?

Eric

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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Thu Oct 21, 2021 2:37 pm

More specifically, in my planned build of a engine with a Chaffin Rajo head, Scat crank with full oil pressure, Bosch dual plug ZR4 mag, dual Zenith SB4F carbs, and a flat (not vee) radiator, should I plan for a water pump too?

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Re: How much HP will the thermosiphon handle?

Post by Henry K. Lee » Thu Oct 21, 2021 2:53 pm

Hank uses water pumps and thermostats on all performance engines. Why? Because it is better to induce than to have it begin a cooking process. Bored engines always have a little more heat as in has less metal in the cylinder. Old rough water jackets and deep pits have a hell of a time in flowing liquid.

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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Thu Oct 21, 2021 10:18 pm

Thanks for sharing your practical experience, Hank. “In theory, theory and practice are the same. In practice, they are not.”

Are there any other performance OHV T builders/owners/operators that would like to add their perspective to the conversation?

Eric

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Re: How much HP will the thermosiphon handle?

Post by Henry K. Lee » Fri Oct 22, 2021 7:39 am

All my overheads use water pumps/thermostats as heat in performance needs to be consistent.

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Re: How much HP will the thermosiphon handle?

Post by John Codman » Fri Oct 22, 2021 11:04 am

I respectfully and strongly disagree with Txgoat2 on less heat. The whole point of an overhead valve setup is to get more air and fuel into the engine and back out of it. More fuel = bigger bang; bigger bang = more heat. The smaller combustion chamber means that each square inch of surface area of the combustion chamber will have to conduct more heat to the cooling system then a larger combustion chamber would.


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Re: How much HP will the thermosiphon handle?

Post by Kevin Pharis » Fri Oct 22, 2021 11:10 am

I found the water pump necessary on my relatively high output flathead (Sherman head). The rear cylinders were not cooling as well as the front, and was sticking pistons after several minutes of sustained load (60 mph flat highway). I suspect that the standard water inlet/outlets will support just about any T motor running today... but at some point the Fronty style water manifold would be an advantage as it would distribute water more evenly throughout the block


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Fri Oct 22, 2021 11:20 am

Combustion chamber surface area is a huge factor in how much heat is put into the cooliing system. A stock T engine's head and pistons and side valve engines in general have a very large combustion chamber surface area exposed to the peak combustion heat and pressure. Most any overhead valve engine of similar bore will have far less combustion chamber area exposed to the peak combustion heat and pressure at any given level of performance. This reduces the load on the cooling system substantially. A flathead engine making 100 HP will require a larger radiator than will an OHV engine of the same displacement making the same power at the same speeds. The Model T engine has a very large combustion chamber area for its displacement and a larger piston head exposure to peak combustion heat than most other engines of similar bore/stroke, T-heads excluded.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Fri Oct 22, 2021 11:28 am

"Water distributor tubes" were commonly used in flathead engines from the 1930s onward to direct coolant flow within the water jacket to critical areas. Water pumps became universal, and pressurized systems began to appear in the early 1930s. Engine designers began to extend water jackets down to near the crankcase flanges to improve overall cooling and thermostats and bypass devices became commonplace.

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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Fri Oct 22, 2021 12:07 pm

TXGOAT2 wrote:
Fri Oct 22, 2021 11:20 am
… A flathead engine making 100 HP will require a larger radiator than will an OHV engine of the same displacement making the same power at the same speeds…
Perhaps true, but not really what we’re discussing. The challenge is a T engine with the same displacement making 2-3x the power and whether or not a water pump becomes more beneficial. Based on the practical experience provided by Hank and Kevin, this appears to be true, and not just for OHV conversions.

Eric

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Re: How much HP will the thermosiphon handle?

Post by George Mills » Fri Oct 22, 2021 12:59 pm

(tongue in cheek but still practical)...you find a Clark radiator core in the book that is the exact same hight as a T, and the same depth as a T, but two columns wider...have the radiator guru clip the end columns off. Add stock top tank, add stock lower tank and you now have a super radiator.

The rad shop guy guesstimated a 4 -5 fold increase in cooling over stock. The car was a 25 Fordor so thats about the heaviest, and from that day on I could never verify his guesstimate...the moto-meter appeared broke as it would appear to not rise under any conditions :) :) :)

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Re: How much HP will the thermosiphon handle?

Post by Hudson29 » Fri Oct 22, 2021 1:17 pm

Pat, doesn't John have a valid point? More power HAS to result in more heat to dissipate surely? If it doesn't go into the motor, where does it go? The only other place I can think of would be out the exhaust system. What am I missing?

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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Fri Oct 22, 2021 2:02 pm

An overhead valve configuration is fundamentally better than a side valve arrangement as far as minimizing heat load on the cooling system for the reasons noted above. Substantially increasing the performance capability of any engine will require attention to the cooling system, especially if it is marginal to begin with. An overhead valve head added to a Model T engine, all else being equal, will reduce the load on the cooling system. It's a better design for several reasons, heat management being one of them. A good overhead valve installation would allow higher performance from a T engine with a stock radiator than would be practical with a side valve arrangement making the same power at the same speeds. It's about combustion chamber AREA and heat transfer. With an OHV, more of the total waste heat goes out the exhaust, rather than into the water jacket. A flat top piston will collect less combustion heat than will a domed piston, or any other configuration that increases the surface area of the top of the piston.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Fri Oct 22, 2021 2:09 pm

Where does it go? Ideally, all of it is expended pushing the piston. But most of the heat released goes out the exhaust or into the water jackets. A good OHV head minimizes heat loss to the water jacket compared to other combustion chamber designs that unavoidabley have a larger surface area directly exposed to the combustion gases. An OHV head also lends itself to having a short, direct path for the exhaust gases to leave the engine.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Fri Oct 22, 2021 2:16 pm

Ideally, a hot rod T would have a water pump that pushed water into the water jacket inlet, a thermostat with bypass, and a radiator of adequate capacity that could be run with a 13 lb pressure cap. A water pump of sufficient capacity would probably require a v-belt or modern type belt drive. About 1,000,000 variables would impact exactly what the ideal setup for any particular build would be.

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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Fri Oct 22, 2021 2:44 pm

TXGOAT2 wrote:
Fri Oct 22, 2021 2:16 pm
Ideally, a hot rod T would have a water pump that pushed water into the water jacket inlet, a thermostat with bypass, and a radiator of adequate capacity that could be run with a 13 lb pressure cap. A water pump of sufficient capacity would probably require a v-belt or modern type belt drive. About 1,000,000 variables would impact exactly what the ideal setup for any particular build would be.
Perhaps true, but not really what we’re discussing. Since this problem has been solved many times before and not wanting to re-invent the wheel, I’m looking for the voices of experience to share what has worked and what hasn’t.

My ‘27 Runabout with a Rajo B, Winfield S-1-BB, and full pressure A crank came to me with a water pump of sufficient capacity with no pump belt, a Three-in-One front plate as seen on pg 132 in “Model T Ford in Speed and Sport”. I was told that the car had no cooling issues during long climbs like Pike’s Peak, and I have observed no cooling issues in my neighborhood of 8% grade hills either.

But for my next build, I plan on using a Matco cross drive under a Bosch ZR4 2 Spark Dual and that appears to conflict with the normal T water pump installations, or maybe not. I have been trying figure out whether or not I have to solve that conflict, and the practical advice given so far is that I should count on having a water pump in my build plans.

Eric


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Fri Oct 22, 2021 2:54 pm

Specific output, duty cycle, ambient operating conditions...

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Re: How much HP will the thermosiphon handle?

Post by TRDxB2 » Fri Oct 22, 2021 4:10 pm

There are "water pumps" and then there a "Model T Water Pumps"
If you look at many of the Model T "water pump" their impeller designs do not incorporate centrifugal force to move fluids. Modern impellers have vanes that flow from the center to the outer edge of a circle. As the impeller rotates, it pulls liquid in at the center, or eye, of the impeller, and the spinning vanes create the centrifugal force that pushes the liquid to the outside of the pump casing, and ultimately out the discharge port.
Model T impellers have blades (like on an old paddle wheel river boat) intended to speed up the flow of the moving coolant. Does a paddle wheeler moving upstream cause the river to flow faster down stream -think not.
Picture a Model T water pump mounted horizontally near the water inlet: the available supply of coolant is whatever passed through the radiator. If there is something slowing down the flow of the coolant to the impeller, the"pump" could not cause the coolant to flow any faster than what is being supplied to it. Also it is doubtful if they have sufficient force to push the coolant into the water jacket, out through the water outlet, up through a hose and into the radiator any more than what is already being cause by thermosiponing.
Model T "water pumps" in the water outlet neck use propellers or impellers. The are being supplied by coolant that was already about to enter the radiator (worthless)
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By Mark Chaffin on Monday, January 25, 2010 - 11:01 pm:
Robert,
Because most people we spoke to indicated a desire for a more refined finish on the aluminum accessories, we felt inclined to give them more value for money. ....
Keith,
The water pump is not necessary if the builder is running a new radiator such as those offered by Bergs or The Brassworks.To be honest, it just looks cool having one attached to the engine for visual effect. Most run water pumps to avoid spending the money on a new radiator. Unfortunately, in the end, they end up chucking the water pump and buying a new radiator after all. Do overheads in general require a water pump? No. They really don't if the engine and radiator are functioning properly (IMHO).
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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Fri Oct 22, 2021 6:25 pm

Interesting that Mark said that, and yet all of his promotional photos of complete engines with his Rajo Reproductions BB head that I have seen show mounted water pumps.

I agree that many of the water pumps made for Ts over the years are useless at best, and harmful at worst. But even in period, there were more effective versions available. The water pump portion of the “Three-in-One Oiling System” from the mid-1920s (like on my Runabout) is described as “a gear driven centrifugal water circulating pump, having a capacity of 8 to 10 gallons per minute, as an integral part of the equipment”. In the 1921 Laurel Motors Special Bulletin 19, they stated that their “Centrifugal water circulators will circulate 5 gallons of water every minute, increasing your present circulation from 7 to 10 times as rapid as gravity - gravity being the method of water circulation in a Ford.” If anywhere close to accurate, it would explain why period racing companies like Laurel Motors and Fronty-Ford recommended the Three-in-One, Tri-Unit, Green Triple front plate, water pump-HT magneto mounts, or other centrifugal water pumps in their “build your own race car” instructions. Each of these systems have the water pump closer to the radiator outlet than to the engine inlet.

In the 21st century, of the 2 common belt-driven T water pumps available from our regular vendors (Snyders, Langs, Chaffins) I believe that the traditional looking one is a centrifugal type, the newer “leakless” Texas T Parts pump appears to be an impeller design. I would believe that either of these pumps would be more effective than ones shown in your photos, but I do admit that I have no experience with either one.

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Re: How much HP will the thermosiphon handle?

Post by Henry K. Lee » Fri Oct 22, 2021 6:50 pm

Eric we have found that Bergs, Atlas, and Texas T works the best. Just my $0.02 worth.

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Re: How much HP will the thermosiphon handle?

Post by Kevin Pharis » Fri Oct 22, 2021 7:28 pm

I have to agree with Mark’s statement... within limits. Most of the overheads we see in operation these days are commercial or production car oriented, rather than race. These heads were typically advertised with additional water capacity and were intended to be direct replacement with minimal peripheral impact to a stock motor. Sure, they can produce impressive results, but were arguably designed to be relatively low performance. Some of the more obscure, exotic, and performance heads have really crowded and indirect water passages, and no doubt would need water pumps regardless of performance level.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Fri Oct 22, 2021 8:41 pm

Ford didn't figure out where water pumps ought to be located until 1937. In a proper installation, the pump draws cool water from the radiator outlet and discharges it into the engine's water inlet port(s), which typically enter the lower part of the water jackets. There are good reasons for this.


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Re: How much HP will the thermosiphon handle?

Post by Kevin Pharis » Fri Oct 22, 2021 9:47 pm

You mean like this...?🤔
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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Fri Oct 22, 2021 10:07 pm

Yep. Compare the early 1930s Ford V8s water pump placement with the later Ford V8 engines with the water pumps located in the block, or the Model A system with most any automotive engine from the mid 1930s on. A stock Model T makes about .09 HP per cubic inch. The Model A makes about .25 HP per cubic inch. Ford added a (half-baked) water pump to the 1928 Model A. As output rose during the 1930s and 40s, from around .25 HP/cubic inch to around .45 HP/cubic inch by around 1950, water pumps, pressure caps, and thermostats became the norm. That suggests to me that the practical limit for specific output on a straight thermosyphon system in an automobile is somewhere around .2 HP per cubic inch for general use.


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Re: How much HP will the thermosiphon handle?

Post by John Codman » Sun Oct 24, 2021 11:40 am

Sorry to beat a dead horse, But it's very simple - you get more power by using a more efficient engine design, in our case valves in head vs valves in block. As I stated earlier, more power requires more fuel and air, and more fuel and air means more heat. The OHV engine will use less fuel then a flathead (for the same power output) due to a smaller combustion chamber volume and avoiding two 180 degree turns for the fuel and air entering and exiting the cylinder. I will agree with you that an OHV engine will generate less heat to develop the same horsepower then a flathead of the same horsepower, but the whole idea of the OHV conversion is to make more horsepower then the flathead. More HP equals more heat, and the load on the cooling system will be greater, not less then the stock engine.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Sun Oct 24, 2021 11:54 am

Flatheads are handicapped compared to OHVs as far as getting rid of heat. That's true at any level of performance. They are also comparatively limited as to the maximum compression that can be obtained and limited as to maximum breathing and scavenging capability. If you want a high performance Model T that looks like a Model T, start with an OHV head. If you don't care what it looks like, run a supercharged flathead with a HUGE radiator and intercooler. You'll need higher octane fuel with the flathead, too.


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Re: How much HP will the thermosiphon handle?

Post by Art M » Sun Oct 24, 2021 2:10 pm

In addition to all of the above, you might consider keeping your engine rebuilder on speed dial.
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Re: How much HP will the thermosiphon handle?

Post by TRDxB2 » Sun Oct 24, 2021 6:35 pm

Interesting study performed by the Society of Automotive Engineers "COOLING CAPACITY OF AUTOMOBILE RADIATORS"
Author(s): E H Lockwood Source: SAE Transactions, 1923, https://www.jstor.org/stable/pdf/44723674.pdf
I think this is very applicable as it was performed on the technology of the time and period engines and radiators.
Types of cores.jpg
cooling capcity speed.jpg
cooling capcity speed.jpg (83.36 KiB) Viewed 4121 times
Basically the study recommends a core value of 50cu.in. per each horsepower. Thermosiphoning radiators are usually 15% larger than pump units. Note no mention of a hybred pump/thermo system
summary.png
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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Sun Oct 24, 2021 7:16 pm

Manufacturers moved away from the straight thermosyphon system as specific output began to rise. Another issue with thermosyphon systems is bulk and weight. They require free-flowing water jackets and comparitively large radiators, which add bulk and weight. At higher engine speeds and horsepower, the coolant needs to be moving fast enough to keep critical, high heat areas, like exhaust valve seats, sufficiently cool and to avoid steam pockets. The thermosyphon system's comparitively low flow rate becomes inadequate, especially in an atmospheric system using plain water as a coolant. In applications where bulk and weight are not a pressing issue, and specific outputs and engine speeds are fairly low, a thermosyphon system can work very well, even where the engine typically sees high loads at high duty cycles, such as in a farm tractor. Kubota was building thermosyphon systems for small tractors until very recently, and may still be doing so. I doubt if Ferrari ever built one. So, pick your lane, and choose your equipment to meet your situation. I don't believe a water pump would be useful on my Model T. If it was making 30 HP or more much of the time, or was a load carrying truck, or used in hill climb events, that would be another matter.

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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Mon Oct 25, 2021 3:28 am

TRDxB2 wrote:
Sun Oct 24, 2021 6:35 pm
Interesting study performed by the Society of Automotive Engineers "COOLING CAPACITY OF AUTOMOBILE RADIATORS"
Author(s): E H Lockwood Source: SAE Transactions, 1923, https://www.jstor.org/stable/pdf/44723674.pdf
I think this is very applicable as it was performed on the technology of the time and period engines and radiators.
Types of cores.jpg
cooling capcity speed.jpg
Basically the study recommends a core value of 50cu.in. per each horsepower. Thermosiphoning radiators are usually 15% larger than pump units. Note no mention of a hybred pump/thermo system
summary.png
Great find, Frank! Real world observations on T era engines. And a specific answer to the question that I started the thread with. And what I infer from table 3 is that the manufacturers of the time were comfortable with almost 30% more horsepower through a given fin and tube radiator core volume with a pump compared to straight thermosiphon.

Keep crankin’
Eric


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Mon Oct 25, 2021 5:20 am

"More specifically, in my planned build of a engine with a Chaffin Rajo head, Scat crank with full oil pressure, Bosch dual plug ZR4 mag, dual Zenith SB4F carbs, and a flat (not vee) radiator, should I plan for a water pump too?"


.......Yes......


Another thing to consider is the fact that a thermosyphon system will not respond immediately to an increase in engine speed/load. A pump system will do so.

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Re: How much HP will the thermosiphon handle?

Post by RajoRacer » Mon Oct 25, 2021 11:08 am

I run a large shaft "water circulator" on my BB RAJO Racer - water pump is a bit of a misnomer as the T's system in non-pressurized.


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Re: How much HP will the thermosiphon handle?

Post by John Codman » Mon Oct 25, 2021 11:22 am

RajoRacer wrote:
Mon Oct 25, 2021 11:08 am
I run a large shaft "water circulator" on my BB RAJO Racer - water pump is a bit of a misnomer as the T's system in non-pressurized.
I'm asking this question because I really don't know the answer - Why does cooling system pressurization have anything to do with whether it's a water pump or a water circulator? The reason for pressurization is to raise the boiling point of the coolant, it has nothing to do with the circulation of the coolant.

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Re: How much HP will the thermosiphon handle?

Post by TRDxB2 » Mon Oct 25, 2021 1:00 pm

ewdysar wrote:
Mon Oct 25, 2021 3:28 am
TRDxB2 wrote:
Sun Oct 24, 2021 6:35 pm
Interesting study performed by the Society of Automotive Engineers "COOLING CAPACITY OF AUTOMOBILE RADIATORS"
Author(s): E H Lockwood Source: SAE Transactions, 1923, https://www.jstor.org/stable/pdf/44723674.pdf
I think this is very applicable as it was performed on the technology of the time and period engines and radiators.
Types of cores.jpg
cooling capcity speed.jpg
Basically the study recommends a core value of 50cu.in. per each horsepower. Thermosiphoning radiators are usually 15% larger than pump units. Note no mention of a hybred pump/thermo system
summary.png
Great find, Frank! Real world observations on T era engines. And a specific answer to the question that I started the thread with. And what I infer from table 3 is that the manufacturers of the time were comfortable with almost 30% more horsepower through a given fin and tube radiator core volume with a pump compared to straight thermosiphon.

Keep crankin’
Eric
Just a caution. I don't consider period Model T "water pumps" as doing any pumping. Their location is about halfway even with the radiator core and their impeller designs do more to rotate a column of water than to push it through the head. If one was mounted lower at the bottom of the radiator core, then they may be of some use.
Last edited by TRDxB2 on Mon Oct 25, 2021 1:09 pm, edited 1 time in total.
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Re: How much HP will the thermosiphon handle?

Post by TRDxB2 » Mon Oct 25, 2021 1:07 pm

TXGOAT2 wrote:
Mon Oct 25, 2021 5:20 am
"More specifically, in my planned build of a engine with a Chaffin Rajo head, Scat crank with full oil pressure, Bosch dual plug ZR4 mag, dual Zenith SB4F carbs, and a flat (not vee) radiator, should I plan for a water pump too?"
.......Yes......
Another thing to consider is the fact that a thermosyphon system will not respond immediately to an increase in engine speed/load. A pump system will do so.
Buy a Berg's radiator and hold off on the water pump, you can always spend the money that later if you need i t. http://www.bergsradiator.com/ They are highly rated by MTFCA members. They have more cooling capacity that others.
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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Mon Oct 25, 2021 1:12 pm

Pressurization will prevent cavitation (bubbles) on the suction side of a pump and also within the pump istelf. It might be possible to build an effective water pump for a T by starting with a "plate" type pump such as were used on some later model applications. I think the MOPAR slant six may have used this type pump, and perhaps some Pontiac V8s. This type pump has the impeller, bearings, seal, and shaft mounted within a plate-like casting a little larger than the impeller. This bolted into the pump volute. A volute could be machined from aluminum or steel. This type pump would probably have excess capacityu, but that would not be an issue if a thermostat and bypass were used. The thermostat would "choke" the pump, limiting volume and horsepower demand while providing some overpressure on the engine block and head. Some 4 cylinder cars may have used a smaller pump of this style.

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Re: How much HP will the thermosiphon handle?

Post by AndyClary » Mon Oct 25, 2021 3:26 pm

Really it isn’t the thermo siphon principle in question. Thermo siphon is physics, it’s gonna happen if you have sufficient capacity to cool the water in the radiator. So the real question is how much hp can the radiator handle. Like Hank said, in a high performance set up a water pump is used to maintain the temperature to eliminate that variable.

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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Mon Oct 25, 2021 4:49 pm

The thermosyphon system is limited as to the speed and turbulence of the coolant flow, regardless of the radiator size. That limits the RATE at which it can extract heat from an engine.


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Re: How much HP will the thermosiphon handle?

Post by fschrope » Tue Oct 26, 2021 9:27 pm

FWIW, IHC and John Deere didn't have water pumps until right after WW2 and they cooled fine. They were even running at 100% load most of the time. Of course, they had plenty of water and a large radiator. The Model T has neither of these though.

My '23 TT has a water pump that was put there by the previous owner/rebuilder. It will pump a lot of water. You can look inside the cap and see the water gushing into the top tank of the radiator even at idle. It has a new radiator and is over heating. Guess what? The rebuilder didn't clean the rust out of the block and head and the water pump forced all these rust chunks into the top of the radiator blocking the tubes. I need to back flush and see it that will force the junk out. If not, I'll have to take it to a radiator shop and have it rodded out. Bummer.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Tue Oct 26, 2021 10:16 pm

Thermosyphon systems also require that the top tank on the radiator be placed well above the cylinder head. The system needs vertical height to allow hot water to rise out of the engine water jacket. A system with the upper radiator tank level with the cylinder head will perform very poorly. A system with the upper tank below the level of the head won't work at all.

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Re: How much HP will the thermosiphon handle?

Post by TRDxB2 » Tue Oct 26, 2021 11:00 pm

The real deal!
Water pump.png
-
-
And there are more of these - for a lot less :?
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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Wed Oct 27, 2021 10:47 am

ALL ORIGINAL SUPER RARE MODEL T HIT OR MISS WATER PUMP! 10 in stock buy it now for only 2999.99!!!


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Re: How much HP will the thermosiphon handle?

Post by got10carz » Wed Oct 27, 2021 1:34 pm

Here is my setup. Big cam, Chaffin head, Warford with 3.23 gear. Keeps up with modern traffic, no water pump. Only heard it gurgle twice. NEW LOW RADIATOR.
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Re: How much HP will the thermosiphon handle?

Post by Jerry VanOoteghem » Wed Oct 27, 2021 3:16 pm

TXGOAT2 wrote:
Mon Oct 25, 2021 4:49 pm
The thermosyphon system is limited as to the speed and turbulence of the coolant flow, regardless of the radiator size. That limits the RATE at which it can extract heat from an engine.
Not entirely "regardless" of radiator size. The rad needs to have the capability to dissipate heat energy at a rate greater than or equal to what the engine can produce. In addition to size, the condition of the radiator plays a role as well. Loose fins decrease heat transfer and slow the thermosyphon. Rough or clogged tubes cut down on flow, which stiffles and slows thermosyphon. Lots of comments here focus only on the heated coolant in the engine as the prime mover in the thermosyphon process. But, it's also the heat transfer from the radiator that causes the coolant temp to drop and therefore the coolant to move to the bottom of the radiator. BOTH the heat producer & the heat dissipator work in unison to initiate and maintain the flow.

Yes, rate is crucial. The coolant can only absorb so much heat energy. When "overloaded" with heat energy, the coolant begins to boil. Therefore, the rate at which the coolant flows through the system must be sufficient. (I compare this to a freight train of coal cars moving along as an overhead conveyor loads in the coal. If the train goes too slow, the freight cars begin to overflow. They can't can't move out all the coal being delivered to them.)

If the engine is producing more heat energy than the radiator can dissipate, (for various reasons), you get boiling.
1. Problem with the engine but otherwise excellent cooling system = boiling. Address engine issue.
2. Engine is fine, low flow in the system due to clogged radiator = coolant boiling in the engine & cold in the radiator. Maybe a pump will help... or a new radiator... or a flush...
3. Engine is fine, old radiator with loose fins = boiling in the engine & a very hot radiator. Pump probably won't help. New Radiator!
4. A "Racing" engine that makes so much heat that thermosyphon can't possibly flow fast enough before the coolant can no longer absorb additional heat & boils, even with an excellent radiator = Add a pump*

*At what HP does this happen? I'd say way too many variables to predict that. (At least for my pea brain :? )


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Wed Oct 27, 2021 3:52 pm

**************"*At what HP does this happen? I'd say way too many variables to predict that." ************
Correct. OP's original question has no specific answer. Your thermosyphon speedster would cool better with a taller radiator that had the same effective surface area as your low radiator. Evidently, what you have is sufficient for the demands you place on the system.

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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Wed Oct 27, 2021 9:52 pm

TXGOAT2 wrote:
Wed Oct 27, 2021 3:52 pm
**************"*At what HP does this happen? I'd say way too many variables to predict that." ************
Correct. OP's original question has no specific answer. Your thermosyphon speedster would cool better with a taller radiator that had the same effective surface area as your low radiator. Evidently, what you have is sufficient for the demands you place on the system.
Which is why I quickly adjusted the thread to ask for practical experience, not theoretical musings. Theory can end up running in circles (as evidenced by this thread) with individuals and consensus taking the definitive positions of yes, no, and maybe at different times. Luckily, a small number of posts, both here and offline, came from folks with real-life experience building and running high output T engines and whether or not they found water pumps to be needed or desirable. Those contributions, along with the nifty period SAE cooling study have provided good data to rationalize my build plans. By receiving more real data points from the type of system(s) that I am considering, I can avoid making my choices based on outliers or off topic solutions.

My thanks to the board for a lively discussion. I’m sure that there is still more that some will want to discuss…


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 28, 2021 9:55 am

Uneeda pump. ///// www.epi-eng.com


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Re: How much HP will the thermosiphon handle?

Post by Jerry VanOoteghem » Thu Oct 28, 2021 12:47 pm

ewdysar wrote:
Wed Oct 27, 2021 9:52 pm
TXGOAT2 wrote:
Wed Oct 27, 2021 3:52 pm
**************"*At what HP does this happen? I'd say way too many variables to predict that." ************
Correct. OP's original question has no specific answer. Your thermosyphon speedster would cool better with a taller radiator that had the same effective surface area as your low radiator. Evidently, what you have is sufficient for the demands you place on the system.
Which is why I quickly adjusted the thread to ask for practical experience, not theoretical musings. Theory can end up running in circles (as evidenced by this thread) with individuals and consensus taking the definitive positions of yes, no, and maybe at different times. Luckily, a small number of posts, both here and offline, came from folks with real-life experience building and running high output T engines and whether or not they found water pumps to be needed or desirable. Those contributions, along with the nifty period SAE cooling study have provided good data to rationalize my build plans. By receiving more real data points from the type of system(s) that I am considering, I can avoid making my choices based on outliers or off topic solutions.

My thanks to the board for a lively discussion. I’m sure that there is still more that some will want to discuss…
Can you share with us your decision, based on the "real world" experiences of others? Might help to us all... I, for one, would like to know, rather than to "muse" :)

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Re: How much HP will the thermosiphon handle?

Post by walber » Thu Oct 28, 2021 1:08 pm

Real world - I run A "T" head on my speedster, A crank with domed pistons, Stipe 280 Cam and a Zenith HP5A carb that I replaced with a Weber a few years ago. I have a high radiator that has a modern recore from probably 15 years ago. No pump and I've never had overheating issues. If anything, it runs too cool. Sustained driving at near 2000 RPM, climbed Pikes Peak and many other mountain trips. For whatever reason, Thermosyphon has worked just fine in my world.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 28, 2021 1:11 pm

My dad mentioned that T racers in this area used to add a "water tank" to increase water capacity for more cooling. That would allow the car to run longer before it overheated, but it did little to actually get rid of heat at a higher rate. Adding cooling fins to the water return pipe would probably do as much. A flat tube radiator and a water pump is the best arrangement for most all automotive applications. Where weight and space are not considerations or where specific output is very low, as with a stock Model T, a thermosyphon system is adequate for most general service.


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Re: How much HP will the thermosiphon handle?

Post by 2nighthawks » Thu Oct 28, 2021 1:14 pm

Walt,....you said,...."I run a "T" head,...." I thought your speedster had a "Fronty" head,...???


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 28, 2021 1:15 pm

My '27 roadster is mostly stock with a Berg radiator and no water pump. It will run all day at 2000 RPM in 98F heat without overheating. I use "green" antifreeze at about 50/50.


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Re: How much HP will the thermosiphon handle?

Post by John Codman » Thu Oct 28, 2021 2:47 pm

fschrope wrote:
Tue Oct 26, 2021 9:27 pm
FWIW, IHC and John Deere didn't have water pumps until right after WW2 and they cooled fine. They were even running at 100% load most of the time. Of course, they had plenty of water and a large radiator. The Model T has neither of these though.

My '23 TT has a water pump that was put there by the previous owner/rebuilder. It will pump a lot of water. You can look inside the cap and see the water gushing into the top tank of the radiator even at idle. It has a new radiator and is over heating. Guess what? The rebuilder didn't clean the rust out of the block and head and the water pump forced all these rust chunks into the top of the radiator blocking the tubes. I need to back flush and see it that will force the junk out. If not, I'll have to take it to a radiator shop and have it rodded out. Bummer.
IMHO if the "rebuilder" didn't start with a spotlessly clean block and head, it ain't a rebuilt engine.

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Re: How much HP will the thermosiphon handle?

Post by ewdysar » Thu Oct 28, 2021 3:28 pm

TXGOAT2 wrote:
Thu Oct 28, 2021 1:15 pm
My '27 roadster is mostly stock with a Berg radiator and no water pump. It will run all day at 2000 RPM in 98F heat without overheating. I use "green" antifreeze at about 50/50.
Which supports the very first sentence of this entire thread. “We all know that a well working Ford thermosiphon system will easily dissipate the heat from a stock 20hp T engine.” But that conversation has been covered by so many other threads, that I was hoping to keep the focus on people’s personal experience with high output T engines.

Keep crankin’
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Jerry VanOoteghem
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Re: How much HP will the thermosiphon handle?

Post by Jerry VanOoteghem » Thu Oct 28, 2021 4:11 pm

TXGOAT2 wrote:
Fri Oct 22, 2021 2:02 pm
A good overhead valve installation would allow higher performance from a T engine with a stock radiator than would be practical with a side valve arrangement making the same power at the same speeds. It's about combustion chamber AREA and heat transfer.
It's about efficiency. Heat is energy. Heat rejected by the radiator or out the exhaust is wasted energy, not converted to HP, and that cuts down efficiency. Overhead valves, higher compression, etc. increase efficiency and should reduce waste heat.

I'll stop now. :)


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 28, 2021 4:20 pm

OHV engines have been built with a very wide range of specific output. All else being equal, an OHV engine will make less demand on the cooling system than an L head or T head engine.

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Re: How much HP will the thermosiphon handle?

Post by walber » Thu Oct 28, 2021 5:39 pm

Error in my post above, I use a Fronty "T" head. It's the lower compression version thus the addition of domed pistons. Measured compression is 98 to 100 PSI. The performance is all I need, really pleased with that engine mated to a Chicago transmission and 4 to 1 rear gears.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 28, 2021 6:29 pm

Re: "....no water pump. Only heard it gurgle twice. NEW LOW RADIATOR."

Your low radiator appears to be mounted a good 3" above the stock height.


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Re: How much HP will the thermosiphon handle?

Post by Scott_Conger » Thu Oct 28, 2021 7:01 pm

some sort of a custom body...
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Re: How much HP will the thermosiphon handle?

Post by got10carz » Thu Oct 28, 2021 7:42 pm

Pat, engine is mounted on Essex frame. Raised for clearance.


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Re: How much HP will the thermosiphon handle?

Post by TXGOAT2 » Thu Oct 28, 2021 7:56 pm

Regardless, higher is better, within reason.

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