Carburetor Heat Shield

[steve1973]

Hello all. I'm thinking of making a carburetor heat shield for my halftrack. I'm having some vapor lock problems with my halftrack. I've tried EVERYTHING. I am hoping a heat shield will do the trick. Has anyone done this already? Does it help? please post some photos if you have. Greatly appreciated. I did find a photo of a 1948 White fire truck and it has a heat shield in place. What do you guys think?



If I do this is anyone else interested in one? Let me know.

Steve A.

[autocar925]

Steve,
I sent you a PM

[col.halftrack]

I have at least one of these from scrapping White engines. It may help.

[autocar925]

Due to our crappy California gas, vapor locking is a major problem with my track.  A few years ago I built a heat shield and meant to post it but I lost my camera.  Found my camera so here are the pics and long term results.

The carb sits right on top of the exhaust manifold.  When you shut the engine down, the carb gets heat soaked so the gas gets boiled out of the carb.  The gas spills into the intake manifold and floods the engine.  To start it up, you have to crank for a long time with the throttle open to clear the excess gas.

McMaster Carr sells sheet stainless steel that is mirror polished on one side.  I bought a sheet and formed the sides up.  Then I machined the sheet for all the required holes.  I installed the shield with the shiny side down, so that it reflects the heat.  On the top side, I used a fabric insulation material and covered it with metallic tape.  This has made a huge difference, but not completely cured the problem.  It will never be completely cured because Calif gas vaporizes so easily that it boils at a low temperature.

One more change that would make a big difference would be to install a second phenolic block between the carb and the shield.  You have to leave the original block between the manifold and the shield to give clearance, so the carb is mounted against the hot shield.  If you put another block between the card and the shield it would help keep more heat out of the carb.  I didn't do it because you would need to use longer carb studs.  No way I'm going to try to remove carb studs after they've been baked for 75 years.

[autocar925]

More pics

[yd328]

I don't know how practical it would be for the halftrack, but what about adding a cool can?  It would require a little bit of plumbing and maybe keeping a small supply of ice on hand. Drag cars use them.

Gary

[autocar925]

Don't think that would work because the problem comes in after you shut it down.  It sits there and cooks the fuel off.  With a cool can, the can cools the fuel in the line inside the can and continues to cool the fuel that passes thru the can as the car makes a pass.  The cool can cools the fuel before it gets into the carb, but the problem is hot fuel that is in the carb already.

I've had good luck opening the hood and letting the engine run for a few minutes before shutting it off.  Everything cools down.  After shutting it off I leave the hood open for 15 minutes to let all the engine and exhaust heat escape.  Kind of a pain, but this plus the heat shield stops the vapor lock problem. 

[big44maghunter]

If the problem was bad enough that you had to add something non-standard and that doesn't bother you, why not use heat wrap on the exhaust manifold?  I wrapped the headers on my big block dodge 29 years ago and it has held up very well.  Works well enough that I can touch the header right at the head while it's running with my hand.  I wouldn't keep it there long but if it wasn't wrapped it would burn me instantly!  Just a thought.
Brad

[autocar925]

The way the intake and exhaust manifolds bolt together, I’m not sure you could wrap it.  If you could, I’m sure it would be a big help.  The nice thing about the heat shield is that it is removable anytime you want.  As far as being modified from stock, if the halftrack is undriveable , my thought is that it’s kind of irrelevant whether it’s factory or not.

[steve1973]

That is a great design!! Do you happen to have a drawing of it with measurements to reproduce? That would save me a lot of work if you do. I can drop of the drawing to my fab shop next week to have one made up. My email address is htmotorpool@gmail.com. If I get a drawing and make one up for myself I can also get some made for others who want one.

As for fuel, what are you using? I've been reading a lot on this and a few issues back in Military Vehicles Magazine there was a good article on this topic. The higher the octane the fuel is the lower the temp. is for boiling which in our case causes vapor lock. I've been using clear premium which has no ethanol but is 92 octane. I've been tempted to run the regular stuff at 86 octane but it has ethanol. Also, I read there are different blends used for the summer and winter seasons which also changes the boiling temps of the fuels meaning winter fuels will boil at an even lower temp. If I remember right the manual says regular leaded fuel of 72 octane is recommended.

Steve A.

[big44maghunter]

my thought is that it’s kind of irrelevant whether it’s factory or not.

Completely agree.  Another thought is ceramic coating the exhaust manifold. I've heard that will help retain the heat better.   Not sure if this is true but worth checking.
Brad

[autocar925]

I’ve thought about ceramic coating also.  If I ever remove the manifolds, I am going to get the exhaust coated.  I was at a car show and saw a car that had rust colored coating and it was very hard to tell it was coated

Since the tracks suck so much fuel, I just use whatever is cheapest.  Calif has ethanol in everything so switching fuel grades doesn’t help.  We also have unique fuel specs so that our refineries produce Calif fuel only.  There is gas for 49 states and gas for Calif., so I’m guessing that may have something to do with the vapor lock problem. 

I make drawings for everything, so I’ve probably got plans somewhere.  I machined the shield, but laser cutting has gotten so common that it would be easy to get it lasered cheaply.  I’ll check.

[yd328]

  Also, I read there are different blends used for the summer and winter seasons which also changes the boiling temps of the fuels meaning winter fuels will boil at an even lower temp.

Steve A.

That is correct, the winter blends make the already bad fuel worse.

Sounds like having the manifolds ceramic coated and the heat shield in place would be a big help.

Gary

[steve1973]

So, here is my engine problem story.
Before I rebuilt my engine It ran great with no vapor lock problems what so ever. So at that time I was using an electric fuel pump as that was the way it was set up. I added an AC glass bowl fuel filter at the carb and a pertronix ignition module in the distributor. All fuel lines are new as with the gas tanks.

After the engine rebuild I switched to a mechanical fuel pump, still used the same fuel lines and gas tanks. Other than that I did two more things. I added an MSD ignition module for better spark and ceramic coated the exhaust manifold. Now I get vapor lock. I've tried everything. Bypassed everything. I even switched back to an electric fuel pump, removed all fuel filters, switched carburetors and so on. I still have vapor lock.

 I've been told by many that the ceramic coating should draw much of the heat away not creating more. I had the idea of comparing manifold temps using my coated manifold and Don's un-coated one. But we found out that out Harbor Freight temp guns were way off on their readings and with each other so this has not happened yet.

The one other non engine change that happened was sealing the space around the radiator with correct welting. I had no welting before allowing for air to go around the radiator allowing for a hotter engine compartment.

I did try driving the halftrack with the hood sides up and had same results. All this time the engine temp is normal, never overheating. So this is my engine story.

Steve A.

[spillmk1]

Steve,
I think the fuel is a big factor as you stated earlier.
These engines don't need a lot of octane and
all the additives along with higher octane isn't helping us any.

Here's an interesting read...
https://forums.aaca.org/topic/155995-can-boiling-point-of-gas-be-raised/


Keith