Fuel tank return line

ray greenwood · Post by **ray greenwood** » Fri May 24, 2002 11:47 pm

I have no info on the fuel cooling aspect, but consider this, the fuel in the loop spends less than 8 seconds in the engine compartment. Thats about how long it takes an FI pump to drain a pint from a quart jar...and blow it out the return line...so I'm betting heats not the main reason. Actually, from my experience, return lines are used for one main reason. Keeping fuel pressure down inside the engine compartment. When you go to a dead end regulator system, it has to be vacume variable for one, and has to use a decntly higher pressure in order to use the higher spring pressures needed to absorb the pulses..AND... feed the injection rate without having volume loss. Most dead end rails run 36-42 PSI...but also use solid rails and metal feed lines. These were quite expensive to fabricate in the D-jet and early L-jet days. The higher the pressure at a given volume, the smaller the pintel on the injectors. The regulators on dead end loops are actually just fuel accumulators with vacume diaphram assist. As for the accumulator I used...its from an 82 sirrocco. I used a pipe cutter to lop the end off of the spring chamber...thats the dry end. I put a smaller spring in it, drilled a hole in the end, welded on an 8mm nut for an adjusting screw, put a freeze plug from a small block chevy down inside for an adjusment cup...and tack weded it back togethet in four spots with a mig welder. I used the 8mm adjusting scre with a locknut to adjust the holding pressure. Hint...submerge the diaphram end in water..both to keep from sparking up the vapors and to keep from melting the diaphram when welding. Ray

Bruce2 · Post by **Bruce2** » Sat May 25, 2002 12:39 am

Ray, Pillow, there's one thing you don't know. FI Beetles don't have the filter screen in the tank. And Supers never had it either.

ray greenwood · Post by **ray greenwood** » Sat May 25, 2002 7:18 am

Thats interesting.Learn something every day! They do have a long inlet tube that fits the swale in the bottom of the tank though (well relatively long). I had just assumed that the ones I had worked on, had the sock filter removed already. Maybe the factory got smart? Who knows. The pump on all of the fuel injection can cavitate easily in shallow fuel. Generally the sock filter was there to keep the sediment that collects in the pool, out of the fuel line I can find no other reason for needing that lower deck area in the tank. Although it would have been just as simple to put a narrow funnel shape in the bottom and run it down to the last drop....but that would pull all of the sediment into the fuel line. The sock filter was unnecessary...in my opinion. Thanks for the info! Ray

Post by **Tom Notch** » Sat May 25, 2002 8:10 am

Ray, Have you looked at the link I posted above?? There is the inside of the fuelie tanks showing the "dog bowl".

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Tom Notch
Tom's Old VW Home

Bruce2 · Post by **Bruce2** » Sat May 25, 2002 10:57 am

Look at that folks, Tom makes VW history. You've heard of "elephant's foot" tail lights, "doghouse" fan shrouds, "rhino" case transmissions. Now Tom coins the term "Dog Bowl" fuel tanks.
Ray, I think the reason they removed the sock filter screen was like you say to do with preventing cavitation in the pump, and the fact that they have that big fuel filter by the pump anyway. The length of the pickup tube inside the tank is only about an inch long. But now you bring it up, I think I'll cut mine shorter to give that extra bit of cruising range.

ray greenwood · Post by **ray greenwood** » Sat May 25, 2002 12:33 pm

Tom...thanks for the pics! All of the type 3's I have owned...all injected, and I have never noticed. The type 4 has nothing that comples...but does have a 3" deep square indention about 5x7 inches I think...in the bottom. I have never had any problems on the type 4 ven running on fumes. But the type 3 tank is flatter on the bottom than the type 4. The fuel pick-up tube on most type 4 is about 5 inches long with a bend in it to keep the tube and the sock about 1/4" above the flat bootom of the square indention in the bottom of the tank. I have seen tubes longer than 2" here and there in other models. Dang....too many parts...too many years! Thanks! Ray

Pillow · Post by **Pillow** » Tue May 28, 2002 11:02 pm

Very intersting Bruce2. From my experiences with bus FI there is still a sock in them though, I was just *assuming* the same would be true for other VW models, my bad.

Ray that is truely impressive how you changed that pressure reg!

I am still cleaning parts for the T1 CIS project in the bus. Hopefully in a few weeks I can post something productive

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Adrian Pillow
'66 VW Westfalia - "Biscuit"
'67 VW Deluxe Westfakia - "Dino"
'79 Porsche 911 SC - "Cochese"

Hebster · Post by **Hebster** » Tue May 28, 2002 11:21 pm

Do you have any pictures of your different types of tank configurations? I'm working on my split -52 and trying to figure out how to make the tank for my FI.

ray greenwood · Post by **ray greenwood** » Wed May 29, 2002 3:53 pm

Pillow, the thing I didn't mention, was that I screwed up three of them before I figured out what I was doing...thank god for cheap junk-yards around here! But I learned alot....like that four little tack welds would hold just fine..instead of trying to barbecue a solid bead around it...with my limited welding skills. Ray

Post by **Tom Notch** » Thu May 30, 2002 5:15 pm

Heb, I'm just gathering some items for my '51 efi conversion. Actually I'm just dropping the split onto my '69 pan and running gear which is already an efi car.

I've been thinking of doing another tank bottom graft. I have both T1 (standard, 1302[?] but with efi) and T3 efi fuel tanks setting here and 2 '51 tanks, 1 rotted out and the other is perfect. I'll cut the t1 and T3 bottoms out plenty big and then the rotted tank will be my "test" tank.

I "think" I can re-shape the bottom out of the late T1 tank to replace the '51 tank's rotted bottom. And with the nice convoluted bottom of the late tank, made for clearance and increasing the capacity of both the tank and the trunk above, I may be able to get another gallon or 2 into the original but now efi equipped, 8 gallon tank.

I would have to trim and bend up the graft to match the lower section of tank's sides. This would give me a retangular shaped "pan" with maybe 2" deep sides. I set the tank into the tank opening in the car and drop the bottom, the graft piece, down to the same tank to front suspension and pan clearance as my stock '69 T1 had.

The T3 tank has a much flatter bottom and I feel would be pretty easy to graft into the '51 tank. That's my backup plan. You can see pix of one on the link I posted above or click on my signature and go to my site. But it would still be about 8 gallons. I'll know by maybe Oct. which way to go.

And it will look stock from the top,

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Tom Notch
Tom's Old VW Home