Welding a sump on the fuel tank

[Gordonm]

Thinking of going to EFI and if you are running a exteranl pump it would seem best to have a small sump on the tank. Where is the best location and how is it done. It looks like the cross brace tha tholds the tank in is in the way. Or is it just better to put in an AN fitting at the bottom of the tank?

 

[mrvette]

Thinking of going to EFI and if you are running a external pump it would seem best to have a small sump on the tank. Where is the best location and how is it done. It looks like the cross brace tha tholds the tank in is in the way. Or is it just better to put in an AN fitting at the bottom of the tank?

I have had DPFI with rear gravity fed pump in the rear, strapped to the tank, and pressuring the lines going forward, since installing the system some 15 years ago...main trouble is when the tank runs lo, the pickup sock runs dry with fuel slosh and then the engine stumbles....takes it down to maybe 1-2 gallons in the bottom before that happens....

I have considered many a adaptation to the tank to cure the problem, but the only cheep device I have found that's at all trustworthy for the use is a 5 gallon air tank is at Harbor Freight...used as a portable air tank ....

but the rub is still to keep the feed off the stock fuel pickup and so the damn gauge level sender is mounted to it, and so then to do what??

never quite closed loop on it yet....maybe this winter, then to mount the air tank in position, and ensure feed for the pump under all conditions....

maybe then to have a drain to get water out....entirely another issue for ME alone....

:gurney:

 

[Twin_Turbo]

The sump I used here is the one from comp. eng. and it needs to be shortened and welded on backwards. Do it the other way around and/or a full length install and you will not be able to reinstall the tank on a bumper car because of the rear crossmember:





This is the ONLY location where it fits. Any further back and you won't be able to install the tank, any further forward and the tank crossmember won't fit.

The same sump welded to a dodge tank after replacing the whole bottom:

 

[Gordonm]

Thanks TT. That is exactly what I was looking for. The picture tells it all and I see how it was shortened to fit. It looks deep enough so it will not starve for any fuel. Good place to mount the fuel pump also as I am running a dual mount spring also. Thanks for the info.

 

[MYBAD79]

Why not use a F-body internal pump ?? Walbro makes a nice replacement pump if you want more flow. Just an idea....



These can be found cheap on junkyards, maybe the pickup has to be extended to fit the deeper tank on a C3 but there won't be any fuel lines under the tank...

 

[Gordonm]

The F body pump is another option I have been looking at also.

 

[grumpyvette]

the work above is IMPRESSIVE, I know because IVE welded on several sumps , on gas tanks,and even custom fabricated a few gas tanks from aluminum sheet stock and diamond plate, but the main point is you can frequently buy a complete fuel cell for a reasonable cost. thats set up correcly for far less total cash, time,effort.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-293220&N=700+115&autoview=sku

 

[Twin_Turbo]

Building an aluminium tank is a major PITA!!!

 

[mrvette]

Nice tank there TT, my buddy built a 200 gallon one for a 28' twin engine Chris Craft some years ago...that was a hell of a project in his driveway for a couple weeks in the evenings.....he was getting really tired of it by the end....he used diamonplate and reinforced it all over hell inside....thought the damn thing weighed a ton ......:flash:

 

[Gordonm]

I talked to a customer of mine who welds for a living. He said no problem. He welds on tanks with fumes all the time. He will fill it with an inert gas and Tig it on.

One question though, I will probably use a sump like this http://store.summitracing.com/partdetail.asp?autofilter=1&part=CEE-4041&N=700+115&autoview=sku

Will the return line being close to the intake line have any problems. Will the turbulance from the return hamper the flow on the intake side. I could have him weld in a seperator between the two nozzles.

 

[Twin_Turbo]

That's the same sump as used in my pics. You want the fuel to return to the top of the tank, wether you're using carb or FI, if you have the return on the bottom, the whole column of fuel in the tank will pressurize the return and that will affect fuel pressure. With the carb it may even raise the pressure abovewhat the carb can handle if the tank is pretty full. With FI it will pressurize the return line and this will affect fuel pressure also.

 

[Gordonm]

So I should just block off one of the lower ports and put in a return bung on the top of the tank. The splashing of the fuel in a tank that is not full will not cause a problem?

In your picture what is the other line on the sump used for?

 

[mrvette]

That's the same sump as used in my pics. You want the fuel to return to the top of the tank, wether you're using carb or FI, if you have the return on the bottom, the whole column of fuel in the tank will pressurize the return and that will affect fuel pressure. With the carb it may even raise the pressure abovewhat the carb can handle if the tank is pretty full. With FI it will pressurize the return line and this will affect fuel pressure also.

Years ago, when I first had the fuel slosh problems, noticing the engine stumble in a hard corner with lo tank, I stuck a fuel filter in the tank output line with the third line from the return into it....but the fule pump apparently ran into cavitation, made a really bad grinding noise sound...even though the car seemed to run ok, I took it out on account of that pump was not a happy camper and I didn't want any problems....:crap: so I gave up on that concept, and put the return into the top pass side as per stock for a '72....still running the stock lines too work fine for my DPFI install....

thinking of a 5 gallon air tank for a add on under there somewhere....

add capacity and act as a sump...:gurney:

 

[Twin_Turbo]

So I should just block off one of the lower ports and put in a return bung on the top of the tank. The splashing of the fuel in a tank that is not full will not cause a problem?

In your picture what is the other line on the sump used for?

I hooked it up to the top. This tank already had a 5/16 return line there, I also blocked off the original feed on the inside and put a yellow plastic cap on the outside end.

The pic is not the final setup, it's when I was playing around with the lines to see what the best solution would be. This is what I ended up with:






The other port is simply blocked with a allen style NPT plug

 

[Z-man]

So I should just block off one of the lower ports and put in a return bung on the top of the tank. The splashing of the fuel in a tank that is not full will not cause a problem?

It's not the splashing so much as the possibility that the tip of the suction line to the fuel pump will become uncovered with fuel. This could happen with a low fuel level in a turn, for example. If this happens, even for a split second, air is drawn into the line forming a bubble. It's harmful to the pump and when the bubble hits the injectors you'll get a misfire or a complete stall of the engine.

I re-used my sending unit and mounted a sump below the tank. It's worked pretty well now for a few years. Since the sump is actually below the tank, my gauge will read empty even when there is a gallon of gas covering the pump suction line. No chance of air getting into the line. I return the fuel at the bottom of the tank (blue line) so that there is no aeration or foaming of the fuel when it is returned to the tank.

I also left the sending unit in the tank and just capped off the old line. That way the gas gauge still works.

Returning the fuel at top or bottom make no difference from a weight standpoint (TT), because gasoline just doesn't weigh that much. The static pressure from gravity on a foot or two of gas is negligible...and if both feed and return are from the same tank, the net differential is zero (otherwise, you'd have perpetual motion).

 

[Twin_Turbo]

Gas weighs about 3/4 of water so .75kg/L roughly. You;'re right, no communicating vessels but you're right, the pressure difference between feed and return is 0, I didn't think this through at all :footmouth:

 

[Gordonm]

What I think I might do is to take the sump that is pictured and weld it to my tank as pictured. Before putting the sump on if I put in a baffle between the inlet and outlet port there should be no turbulance between the 2 ports. This would be quite simple to do. My tank never seems to get that low on fuel and with the sump being below the tank and small enough I doubt it would get uncovered. I'll keep the sending unit for the gas gauge and just block off the line.

 

[mrvette]

So I should just block off one of the lower ports and put in a return bung on the top of the tank. The splashing of the fuel in a tank that is not full will not cause a problem?

It's not the splashing so much as the possibility that the tip of the suction line to the fuel pump will become uncovered with fuel. This could happen with a low fuel level in a turn, for example. If this happens, even for a split second, air is drawn into the line forming a bubble. It's harmful to the pump and when the bubble hits the injectors you'll get a misfire or a complete stall of the engine.

I re-used my sending unit and mounted a sump below the tank. It's worked pretty well now for a few years. Since the sump is actually below the tank, my gauge will read empty even when there is a gallon of gas covering the pump suction line. No chance of air getting into the line. I return the fuel at the bottom of the tank (blue line) so that there is no aeration or foaming of the fuel when it is returned to the tank.

I also left the sending unit in the tank and just capped off the old line. That way the gas gauge still works.

Returning the fuel at top or bottom make no difference from a weight standpoint (TT), because gasoline just doesn't weigh that much. The static pressure from gravity on a foot or two of gas is negligible...and if both feed and return are from the same tank, the net differential is zero (otherwise, you'd have perpetual motion).

OK, I see the red finned pump and what looks like a filter before it,....

that silver canister looks like something custom, and you say only about a gallon, I thinking of adding maybe 5 gallon steel can down lo in front like what you have....

How did you get those blue line fittings into the bottom of the tank, looks like a fitting was welded, or somehow you had to get inside the tank to hold a bolt/washer/fitting for the thing to screw into....so that issue is what's stopping me from advancing with my idea....which basically is to use the stock gas feed into the 5 gallon tank top, and then out the bottom of that into the filter/pump setup....for one thing, that concentrates the water accumulations to the small tank bottom, and then easy to drain it all....

BTW, my car is still running fine, but have not gone through the second tank yet since the cleanout.....

:hissyfit:

 

[Z-man]

OK, I see the red finned pump and what looks like a filter before it,....

that silver canister looks like something custom, and you say only about a gallon, I thinking of adding maybe 5 gallon steel can down lo in front like what you have....

How did you get those blue line fittings into the bottom of the tank, looks like a fitting was welded, or somehow you had to get inside the tank to hold a bolt/washer/fitting for the thing to screw into....so that issue is what's stopping me from advancing with my idea....which basically is to use the stock gas feed into the 5 gallon tank top, and then out the bottom of that into the filter/pump setup....for one thing, that concentrates the water accumulations to the small tank bottom, and then easy to drain it all....

BTW, my car is still running fine, but have not gone through the second tank yet since the cleanout.....

:hissyfit:

Here are some details of my tank assembly. I used 90 degree bulkhead fittings and nuts, and also used tank washers (available at the local racing parts store, or Summit, etc.) The washers have gasoline/alcohol safe rubber inserts so they seal leak free. I picked a smooth, flat area and used one washer on both the inside and outside of the tank. Before I installed the fittings, I cut off the excess thread on the inside of the tank and radiused the inlet to reduce the friction of the fuel as it entered the tube (second picture).

I drilled the holes close to the large holes in the Vette tank so I could reach in with my fingertips and hold the nuts on the inside of the tank. Notice the return line fitting on the left (first picture) is near the original sending unit access hole. The pump suction fitting is directly under the gas tank lid hole (second picture). I used a long attachment from my socket set to hold the nut from the gas fill hole. Here's a link if you want to see all the details of my assembly Link

Hope that gives you some ideas!

This shot shows the relative location of the new fuel inlet bulkhead fitting (blue) to the old fuel pickup line inlet. The filter sock has been removed since the fuel pickup tube is no longer being used.

 

[Z-man]

What I think I might do is to take the sump that is pictured and weld it to my tank as pictured. Before putting the sump on if I put in a baffle between the inlet and outlet port there should be no turbulance between the 2 ports. This would be quite simple to do. My tank never seems to get that low on fuel and with the sump being below the tank and small enough I doubt it would get uncovered. I'll keep the sending unit for the gas gauge and just block off the line.

That should work great. Look at TT's setup - the sump is right where the stock pickup used to be located and is probably the best location (at least according to the Chev. engineers). I just was reluctant to weld on my old tank, not knowing how well it would hold.

You might also think about extending the return line into the tank somewhere away from the feed line so you wouldn't have to fool around with a baffle.