Adding a Tap to Gas Tank
- Thread starter GeneBob
- Start date
Ivan in southeast va.
Senior Member
Why would you want to do that?
nkaminar
Well-known member
1. Drain the tank. Leave the cap off and let it air for a while.
2. Use argon or dry ice to displace all the air in the tank. No oxygen should be inside. Using dry ice, lightly put the cap in place to contain the carbon dioxide.
3. Use a sharp punch to punch a hole where you want the new tap from the outside of the tank. The object is to bend the metal into a cylinderical shape with the inside diameter to match a 1/8 NPT pilot hole.
4. Tap the hole with the 1/8 NPT tap. Use Permatex sealant on a brass valve with 1/8-NPT on one end and whatever you need on the other end.
The alternative is to weld or braze a boss onto the tank and drill and tap the boss. Do not use solder. But this is going to create a mess and is best done with the tank out of the car.
2. Use argon or dry ice to displace all the air in the tank. No oxygen should be inside. Using dry ice, lightly put the cap in place to contain the carbon dioxide.
3. Use a sharp punch to punch a hole where you want the new tap from the outside of the tank. The object is to bend the metal into a cylinderical shape with the inside diameter to match a 1/8 NPT pilot hole.
4. Tap the hole with the 1/8 NPT tap. Use Permatex sealant on a brass valve with 1/8-NPT on one end and whatever you need on the other end.
The alternative is to weld or braze a boss onto the tank and drill and tap the boss. Do not use solder. But this is going to create a mess and is best done with the tank out of the car.
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Pete
BANNED
Good process. Works every time. Only thing I can add is put some grease on the tap. It will collect any shavings.
rotorwrench
Well-known member
The gas tank was 12-gauge steel back when it was new. Unless you can look in and still see terne plate in the bottom of the tank then there is a good chance that it is not as thick as it used to be. The OEM outlet bung is generally a relatively thick piece that was riveted into a shallow flat area stamped into the bottom of the tank, They were riveted and then terne plated to insure a good seal.
Welding something thick to something thin is not as easy as welding two pieces that are the same thickness. This is even more difficult if the metal is corroded on the inside. When they corrode, the bottom can be where the most corrosion is and therefore the thinnest metal in the whole tank. A person would have to miss the baffles as well.
My own conclusion is that this is not a good idea. Having some experience with internal tank repair I would not try to do it myself even if the metal was good in the bottom. A person is just adding a potential leak spot for a non essential item.
Welding something thick to something thin is not as easy as welding two pieces that are the same thickness. This is even more difficult if the metal is corroded on the inside. When they corrode, the bottom can be where the most corrosion is and therefore the thinnest metal in the whole tank. A person would have to miss the baffles as well.
My own conclusion is that this is not a good idea. Having some experience with internal tank repair I would not try to do it myself even if the metal was good in the bottom. A person is just adding a potential leak spot for a non essential item.
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J Franklin
Well-known member
Just add a T where the shutoff is.
Joe K
Well-known member
The shutoff valve screw into the gas tank IS a pipe thread?
Maybe be careful your passenger doesn't hit his/her knee on the valve after appropriately lowered?
Joe K
jack backer
BANNED
Put a fuel pump on it
Synchro909
Well-known member
I suspect he might be wanting the second valve so he has a "reserve" of fuel with one tap higher than the other.. If that is so, there is no need for a second valve, just find a valve with two "on" positions and put a higher intake on one just like VW did years ago.
A lot of good information here, thank you. Nkaminar and Pete, I appreciate your best ideas. Rotorwrench, I appreciate your input too, even though you basically are saying don't do it. J Franklin, the tee would probably not work due to the flow but maybe.
I did not tell you that it did not have to be in the bottom of the tank and this might change some of your thinking. However, you will probably ALL think I am an idiot because I am looking at the Holley Sniper fuel injection system which requires a return to the tank. So the return can be up high and should be essentially no pressure.
Again, thank you all, I am still considering the options including forgetting about it.
I originally wanted to mount something like a metal radiator overflow tank up high under the hood that would receive the return flow and be "tee-d" into the feed line thus be close to the height of the gas inside the tank but provide a flow relief volume. My fear is that this would overflow depending on the bypass return flow.
I did not tell you that it did not have to be in the bottom of the tank and this might change some of your thinking. However, you will probably ALL think I am an idiot because I am looking at the Holley Sniper fuel injection system which requires a return to the tank. So the return can be up high and should be essentially no pressure.
Again, thank you all, I am still considering the options including forgetting about it.
I originally wanted to mount something like a metal radiator overflow tank up high under the hood that would receive the return flow and be "tee-d" into the feed line thus be close to the height of the gas inside the tank but provide a flow relief volume. My fear is that this would overflow depending on the bypass return flow.
jack backer
BANNED
^^^ what Wick said or use a fuel cell. You need an accurate electric rpm feed and cut in an O2 sensor..
EFI is great, but for that price I’d tough out a Holley 94,tuned correctly they ‘communicate’ with the engine by vacuum using a power valve..early tech..
EFI is great, but for that price I’d tough out a Holley 94,tuned correctly they ‘communicate’ with the engine by vacuum using a power valve..early tech..
Wick,
I wish I could. I have not seen a mount that didn't require welding to the frame which I can't do. Plus the cost makes this project too expensive.
Jack,
I have an O2 sensor based air fuel ratio gauge mounted to try to tune in the Stromberg and I think I am making progress. The supercharger is throwing me off in traditional tuning techniques.
I wish I could. I have not seen a mount that didn't require welding to the frame which I can't do. Plus the cost makes this project too expensive.
Jack,
I have an O2 sensor based air fuel ratio gauge mounted to try to tune in the Stromberg and I think I am making progress. The supercharger is throwing me off in traditional tuning techniques.
jack backer
BANNED
Emulsion tube carburetor like a Stromberg hard to tune with a blower.. how are you running it? Draw through?… EFI definitely will work. Depending on body style you can buy a bolt in fuel tank.
rotorwrench
Well-known member
There are also saddle tanks available that fit underneath the running board aprons. I've not used them but it may be a way to go without being obvious.
I've cut the tops off of several model A tanks to repair them for corrosion damage. This allows full access to the inside and would help kill two birds with one stone since most tanks are pretty rusty inside anyway.
Until some company starts stamping out those complicated tanks and welding them together to hold fuel, we are stuck with these 90+ year old units.
I've cut the tops off of several model A tanks to repair them for corrosion damage. This allows full access to the inside and would help kill two birds with one stone since most tanks are pretty rusty inside anyway.
Until some company starts stamping out those complicated tanks and welding them together to hold fuel, we are stuck with these 90+ year old units.
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Jack,
I am drawing through the Stromberg. Right now, I am increasing the power valve size to richen up the mix under hard accel. When I am holding constant speed, I am running on the rich side. Once I have good numbers under heavy accel, I will try to lean out the steady speed a little, maybe one step leaner would do it. I don't want lean out the mains until I make the power valve a little more rich.
Rotorwrench,
I was trying to avoid adding gas tanks of any kind.
Thanks,
Gene
I am drawing through the Stromberg. Right now, I am increasing the power valve size to richen up the mix under hard accel. When I am holding constant speed, I am running on the rich side. Once I have good numbers under heavy accel, I will try to lean out the steady speed a little, maybe one step leaner would do it. I don't want lean out the mains until I make the power valve a little more rich.
Rotorwrench,
I was trying to avoid adding gas tanks of any kind.
Thanks,
Gene