MTFCA Forum

I finally took George Akins advice and pressured my fuel tank using the exhaust on my 1924 Depot Hack. For years I have had trouble climbing hills unless my tank was completely topped off.

To the neigh sayers, there is no risk of explosion. Any oxygen in the tank is displaced by carbon monoxide. There is an aticle in the MTFCA Carburetor book which explains how to do this work, taken from Model Airplanes which use the exhaust gas to pressurize the fuel.

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By adding a one way valve, I now have steady pressure in the tank. I also added the stainless fuel filter to act as a spark arrestor.

Look me up at Homecoming in June and I can show you the setup. Here are some pictures.

Yes Rod...., it does work well!

So, your out running your T on a 95 degree day. You notice your fuel is running low, let’s say 1/4 tank. By the time you get home the gas is at 1/8 of a tank with the other 7/8 full of warm air. It gets rather cool over night, the air in the tank cools down. With the one way valve wouldn’t that create a negative pressure in the tank? I’ve heard stories of tanks denting in that situation. I want to add a hand pump to the speedster I’m building, but can’t get a plumbing system in my head to relieve both excess and negative pressure.

Negative pressure doesn’t exist. The one way valve is designed for low vacuum or pressure. Anytime the pressure in the tank goes negative, the valve opens thereby eliminating the condition you are describing of the tank collapsing.

The valve was added because the pressure gauge was bouncing quite a bit with each pulse of the exhaust. Now the pressure stays steady. The tank even holds pressure after the engine is turned off.

schwabd1 wrote: ↑

Fri May 16, 2025 4:51 pm

So, your out running your T on a 95 degree day. You notice your fuel is running low, let’s say 1/4 tank. By the time you get home the gas is at 1/8 of a tank with the other 7/8 full of warm air. It gets rather cool over night, the air in the tank cools down. With the one way valve wouldn’t that create a negative pressure in the tank? I’ve heard stories of tanks denting in that situation. I want to add a hand pump to the speedster I’m building, but can’t get a plumbing system in my head to relieve both excess and negative pressure.

A simple check valve that is held shut when the pump pressurizes will allow air to fill the void. On this example the check valve does exactly that when the engine is off as the exhaust it open to the atmosphere.

My only concern would be to insure there is a shutoff on the carb to prevent a hot tank pumping thru a leaky float valve.

Rod, do you have the same problem with your other T's?

Allan from down under.

My 1910 and 1913 don’t seem to have the same problem as those gas tanks are mounted higher and closer to the carb than the Depot Hack.

My Depot Hack does have a carb shut off valve.

Round tanks and oval tanks are mounted at near identical heights above the frame rails. the oval tanks may look to be lower, but it is only the shape that gives this impression. The last gallon in the tank is at the same height. Being further back, the depot hack may suffer starvation earlier in hilly country, but otherwise the delivery should be the same, if everything else is in order. Adding pressure to the tank simply forces fuel past what may be an unintended restriction. No doubt it may work, but it is treating the symptoms rather than the cause. Or, I maybe barking up the wrong tree, again.

Allan from down under.

I am refraining from responding to this post because I do not want my fingerprints on this if it results in a lawsuit.

I've seen this idea elsewhere and am glad you put it on your hack. No more need to be towed out of deep, off the tour route hollers in Tennessee!

I agree that the modification is ingenious, but their have been literally millions of Model Ts that ran fine without it. I cannot help wondering if you are putting a band-aid on the actual problem?

Based on the thread so far, the T in question is a Depot Hack, and therefore is not stock from the get go. If the gas tank is in a custom location, maybe lower and/or farther back, the gravity feed is less effective while going up inclines, leading to common fuel starvation. Many folks go with a modern electric fuel pump (my ‘27 runabout with the gas tank under the trunk has one), but the OP wanted to try something else. Nobody seems to question if a speedster uses a hand pump to solve the same problem.

If this is working, good for him.

Keep crankin’,
Eric

Sometimes you got to do what you got to do!
Regardless of the cause, of the issue, the solution resolved it.
Good job.

If I remember correctly, Rod's tank is mounted further back on the frame. Noel

You may recall 15 T sedans had the tank under the back seat. Early coups had the tank in the trunk. The solution was to lower the carb with a special, longer/lower intake manifold. I have done this for 2 T's with model A carbs. (lowered the carbs) Works well.

Pressurizing the tank is a solution. Better than a fuel pump that will fail regularly IMHO. Thats been my experience.
So I shy away from electric pumps.

I have heard of pressurizing the tank in a similar fashion, but I dont think a check valve, pressure gage, or spark arrester was used.

Two of my T's have the fuel tank mounted in non-standard locations, both decided by the state Ford agents and distributors for their respective colonial bodied cars. My 1924 Tarrant special tourer has the tank suspended on the original brackets UNDER the spare tyre carrier at the back. It is fitted with a Stewart vacuum tank to draw the fuel to the carburetor, just like Dodges have.
Duncan and Fraser went a different route with my wide body roadster. With a lowered steering column and front seat, the fuel tank was shifted to the front of the integral turtledeck and raised some 7" higher than standard.
One thing they have in common is a 5/16" fuel line. That delivers some 35% more fuel than a 1/4" line.

Allan from down under.

If you live in the mountains and everywhere you go is up hill or down this will fix your gas starving, I did this around six years ago after talking to and seeing George's https://youtu.be/smymG4xlRcU?si=YIq5Y6lEAVcvrkqu.
The 1\8 vent elbow line swivel's when removing cap

Allan wrote: ↑

Mon May 19, 2025 3:45 am

One thing they have in common is a 5/16" fuel line. That delivers some 35% more fuel than a 1/4" line.

Allan from down under.

Yup. I ditched the 1/4" line for 5/16" years ago. No one notices nor cares.

I also have 5/16 gas line , didn't help me going up steep mountains.

Regardless of fuel line size, you are always restricted by (A) head pressure, and (B) orifice size (float valve orifice). You can run a fire hose from your tank to your carb, and you are still trying to flow through the same tiny hole in the carb. Increase fuel line diameter may let you sleep better but by itself, at the exceedingly low pressures we're dealing with, it will not dispense more fuel into the carb by any practical measure

Increase the fuel pressure and you will deliver more fuel to the carb through any given orifice
Increase the orifice size and you will deliver more fuel to the carb with any given fuel pressure

Assuming an original float valve orifice of .125" and (for instance) head of 6", CD of 1 (and water for the purpose of easy calculating) you will deliver .217 gpm at atmosphere
Assuming present commercial float valve orifice of .093" and all the same parameters, you will deliver .120 gpm at atmosphere, so there is your inability to climb hills...you have cut your fuel delivered to the carb in half under all other conditions or variables

calculations for gasoline vs water will show a difference of gpm for gasoline, but those values will still show delivered gpm to be 1/2 at orifice of .093 vs .125 for any given pressure

you have to raise the head to 19.5" when using the .093" orifice to achieve equal liquid delivery as .125" will deliver at a 6" head

either a pressure increase or an orifice increase will solve the fuel starvation problem...and Rod increased pressure (which was nicely executed)

Fun Facts:

• 1 PSIG at the fuel tank is the equivalent of having a 36" head pressure which is like mounting your tank nearly on the roof of the car

• added to orifice size variable, is "turbulence" which is caused by both orifice size and obstructions beyond the orifice (think "needle")

I sincerely hope I do not regret this first General Forum post in 18 months, but I suspect that I will.

Thanks for an informative reply, Scott ! Much appreciated !!

Scott,

I very much appreciate your scientific approach to this problem. Thanks for adding to this conversation. Facts always triumph over opinions.

Rod

Thank you, Scott!

Thank you, Scott. I enjoy and pay attention to your science-based comments. I look forward to your knowledge shared with us. Noel

I have missed you Scott, and your informative posts!


A lot of high end expensive automobiles of the 1910s used exhaust pressure to pressurize the fuel tank and deliver gasoline from far back and/or low level gasoline tanks up to the front. I do not think I have ever heard of one exploding or causing any sort of fire.
Your installation is very neat, and appears practical. Using the check valve (or one way valve) is a good idea, especially on such a short fuel line. Ambient temperature variations otherwise could push some amount of gasoline or fumes forward in the pressure line and spill into the exhaust pipe. Even IF that were to occur (actually unlikely?), it most likely would not be hazardous since the pressure line is plumbed into the top of the gasoline tank. The only gasoline that could push back in the line would be a very small amount of splash that might enter the line when the engine is being shut off (unlikely scenario). The small amount of fumes that could be blown back through the line would never be enough to become explosive in the exhaust line, and would naturally dissipate quickly. Regardless, a check valve adds a layer of security, peace of mind if nothing else.
Some era systems had a vertical loop of tubing in the pressurizing line. This acted as both a fluid and vapor trap as well as additional cooling for the hot exhaust gasses. It also added a layer of security as a sort of spark arrester. A lot of those considerations become moot points under normal use. Once the tank becomes pressurized, providing that the tank or lines are not leaking much, the actual flow of "hot" exhaust gasses is slow enough that more than a few feet of tubing will be cooled quickly enough such that the pressurized exhaust reaching the tank will not be hot enough to cause any harm, and any "sparks" that did manage to enter the line will be practically cold before it can reach the tank as nothing more than a piece of dust.

I have actually wanted to do this to one of my model T speedsters for many years, just never got around to it. I have built/restored and driven five speedsters so far. Three of them were pressurized by hand pumps, which I loved using! One, had a Stewart Vacuum Tank, which I also liked. The other was a simple vented gasoline tank and gravity.

Wayne Sheldon wrote: ↑

Tue May 20, 2025 6:59 am

... a check valve adds a layer of security, peace of mind if nothing else.

It's also an essential item in order for the exhaust pressure system to function. Model N's used an exhaust pressure oiler, complete with check valves. They hold pressure so well, that if you don't purge the pressure after a run, it will continue to flow oil to the fourth main for some time afterwards and make a neat puddle on the driveway.

There's a reprint of a 'Tinkerin Tips' article on Model T fuel systems and fuel starvation in the current Vintage Ford (May-June 2025) pp38-41. A DIY exhaust gas fuel pressurization system is described along with a parts list. Just fyi, jb