Welding stainless gas tank

Well I have a stainless gas tank (Spectra) that I want to add a small sump onto, for the fuel pickup.

I need to buy some stainless sheet to make a little box to weld onto a corner of the tank.

As far as welding stainless, do I need to worry about matching the alloy, because I don't know
what alloy the tank is. I also want to weld in two stainless outlet bungs.

I won't be doing any welding BTW, I will need to find a guy.

Right now I'm just worried about alloy compatibility.

are you sure the tank is stainless ?

I have a custom stainless tank from Rick's Tanks. I wanted to ensure that the fuel pickup was always able to pick up fuel especially when the fuel level was low. It is in a street car. I ended up using Holley Hyramat to get the job done. There is a mid tank baffle in the tank, so I used 2 separate mats to keep the mats in fuel at all times. It saved me from having to add a small sump on the bottom of what was already a low hanging tank.

It is a stock replacement tank, 1970 Cuda, p/n CR8E, They say stainless and it "looks" stainless.

If I were to modify it with an access hatch, to use the HydraMat, I think the costs would get out of hand.

A small added sump shouldn't be too expensive. I want to use an electric pump, Carter 4601HP, so a low pickup is desirable.

You do not need a low sump for these pumps, using your stock pickup will work just fine. The pump should be slightly lower than the fuel level but they still work fine if the pump is mounted beside the tank. You just don't want the pump to have to work too hard on the suction side, that's all. There have to be thousands of these out there in use with stock tanks and pickups. Don't waste your money.

Holley makes several Hydramats that can be attached to the factory style pickup tube and passed through the stock sending unit opening.

https://www.holley.com/products/fuel_systems/hydramat/hydramats/

Hmmm, you guys are making me think.

what makes this material so expensive ?
i realize parts aren't cheap, but some of the prices for hyrdomat makes me scratch my head..........

This is a bit of a hyjack going towards the end goal. You might be doing a low-pressure carb fuel system. My current carb fuel system consists of a steel sump with two bungs welded into my stock tank. You're doing in stainless what I previously did in regular steel. I'm redoing everything more along the lines of what JBC426 is doing. The end goal for me is to have a E85 EFI fuel system that can support 1000+ HP. I have the Stainless Steel version of the OEM tank https://www.classicindustries.com/product/all-years/plymouth/barracuda/parts/ft6020c.html I also have an expensive chunk of 15" x 10" Holley Hydramat. For a fuel pump, I have an in-tank Aeromotive Eliminator fuel pump. The Hydramat is big enough to have one end sit towards the front of the tank to suck fuel when there is under a gallon left and I'm cruising around town. The back of the mat is far enough towards the rear of the tank to catch gas even under a couple of G's of acceleration force and 1/4 of a tank of gas. So the pump won't suck air under a hard launch and it will suck the tank dry under normal driving conditions. I have a methanol/gasoline compatible fuel cell gasket. I need to make an access flange that I can weld onto the tank and then a plate to mount the pump, vent and return lines. I have a guy near me who has a business that specializes in building custom stainless steel exhaust systems so he's going to do the welding for me. The fuel supply and return lines are a mix of -8 stainless hardlines and Fragola -8 (true 0.500" ID) Race-Rite PTFE hose. One other thing that I will include is a Motion Raceworks bypass flexfuel housing in the return line. The flexfuel sensor gives instantaneous % Ethanol and fuel temp. The in/out line for the OEM GM flexfuel sensor is -6 which could be a restriction. Motion Raceworks sells a part that captures the sensor lines and adds a parallel path so that the combined path size is -10. I know that this is a lot of work to put together and it's been pretty expensive to buy all the parts but I want to spend the $$ once and not have to re-engineer the system. I'm not sure what specific alloy SS the tank is made out of but I figure that can't go wrong with making the custom parts out of 304 stainless so that's what I purchased. Photos are not all the same scale.

I also have a Spectra tank that is said to be stainless (nice tank). I got a comp engineering (which isn't stainless) sump and my friend welded it on 3 years ago and it's been great so far. Not saying it's right or wrong. I did use a 3 stage etching/coating/sealer on the inside though.

Thanks Rumblefish !