1972 Bus Type4 EA 1.7 to Ljet?

[Bnanwel]

The tank opening is 7/16”. The copper return pipe is 5/16” od and 1/4” id. If you figure the area of the cross section of the tank opening(.1503in^2) and subtract the area of the cross section of return pipe(.0767in^2) including the wall (5/16”), you get the feed around the return pipe. If you then figure the area of the cross section of the return pipe (1/4”)id. (.0491in^2), you have a cross section that will yield a greater potential feed volume than return volume.

.1503-.0767=0.0736in^2 feed
0.0491in^2 return

And, I’ve been driving it around trying to make it fail. It’s still early, but so far it is very promising. Ultimately, if it becomes necessary to replace the tank with an FI tank, I will. First, however, I’m going to exhaust my mind with finding a VIABLE workaround or not. It’s an interesting project.
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe

[SGKent]

while an FI tank would be best if you come across a clean on within pickup distance, you can always put the issue on your to do list and braze in a return line some time when you have the engine out and can pull the tank. There are ways to work on a gas tank safely. In the meantime, if what you are doing works, go for it. The FI tanks have no filter in them like the carb tanks. The filter is before the pump.
_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[Bnanwel]

I left the sock out and have the square FI filter between the tank and pump.
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe

[SGKent]

I understand what you did now. The small copper return goes thru the body and into the tank.

As to the return, that will work just fine I think. But, I have only one caveat. We were racing at Riverside, Sears Point, Laguna Seca, and Willow Springs on road courses in FP. We had a small oil sender screwed into the block that had an idiot sender on it and an adapter to a nylon oil pressure line. The weight of that sender was less than the CB adapter you have. We were at Willow Springs and the vibrations snapped the sender off the block. We lost oil pressure but caught it just before the engine grenaded. The #2 rod was bent about 50 degrees and the engine was about to chuck it. There is a lot more force on things that hang than people realize. We did not realize it but when I told my mentor, Bill, who was known for the Cosworth F1 and Indy engines he built, about the incident, he said he had seen that before.

If you can think of a way to make that work with the block held on tightly to something so bumps and potholes cannot vibrate it, consider doing that. Most important, get as much weight off it as you can that might flex it from side to side.

_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[Bnanwel]

It is remarkably light, but I take your point. I had the same thought and relieved it as much as possible with cable ties situated to take some weight off and lessen the likelihood of it vibrating loose and leaking. The t is sealed with an o-ring, and I worried it might work its way loose. I’ll definitely be keeping an eye on it.
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe

[raygreenwood]

[zerotofifty]

[zerotofifty]

[Bnanwel]

I had soft copper and compression fittings on the boat; so, the copper is for proof of concept and testing. I don’t really like mixing copper and aluminum anyway. If I still feel that the system is working after a few hundred miles, I’ll swap the copper for stainless. Thanks; that’s an excellent point which I should have mentioned.
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe

[Bnanwel]

Update
I have driven several hours now really looking for problems. The bus is running well, incredibly smooth. So far the fuel return has worked as hoped. I have noticed that a few bubbles still end up in the filter but are not sufficient to cause problems; the pump is cool and having no trouble maintaining volume and pressure. As it is set up now, the return is about 1-1/4” above the bottom of the tank, slightly slanted but basically straight up. Clearly, there is some “aeration” of the returning fuel. I’m wondering if a bend and a few inches of additional pipe to move the returning fuel further from the pickup would have a real impact and limit the bubbles even more. Thoughts?
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe

[SGKent]

[Bnanwel]

That all makes sense. I’ll change the return tube to aluminum and extend it further into the tank. I’m going to get it as close to 90* as will thread into the tank so that it stays fully immersed as much as possible, less agitation. Moving the ball valve off of the fitting is simple enough. Thanks for the input.
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe

[Bnanwel]

Update:
I lengthened the return pipe to move it away from the outlet of the tank. At the same time, I changed the return to aluminum tubing and reduced it to 1/4” to allow more feed volume. This iteration works quite well, no bubbles sucked to the filter even with prolonged run times. I think this is the way to make the cb performance T perform properly in a fuel injection system, a return without changing the tank or robbing a vent.
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe

[SGKent]

Good job. the only thing left is I would remove the heavy shut off valve. If you need one mount it to something solid. They can also leak. I use small fuel line clamps when shutting off the fuel.
_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[Bnanwel]

That pic was during mock up, prior to removing the shutoff. The T/return is now light and fully functional. It really is a joy to drive! Thanks so much for your input.
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe

[SGKent]

[telford dorr]

There is one more detail about FI tanks that you should be aware of. FI tanks have a small bowl structure in them that's a couple inches wide and high. The fuel feed to the pump comes from the center of the bowl. The return fuel line squirts into the bottom of the bowl from the outside through a simple venturi structure. This return fuel drags fuel from the tank into the bowl, causing it to fill up and overflow. The purpose of all of this is to guarantee a supply of fuel to the pump even when the fuel level in the tank is low. Without it, with a low fuel level in the tank, it is possible on hard cornering to temporarily uncover the tank port to the fuel pump, allowing the pump to suck air. While no big deal when feeding a carb, with FI this will cause a temporary loss of fuel pressure, and thus a loss of engine power. Therefore, when using a non-FI tank, it's best to keep a half of a tank of fuel minimum to avoid this problem or, if below a half a tank, to take corners very gently. FWIW
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[raygreenwood]

[Bnanwel]

Thanks guys. I’m aware of the potential “slosh” problem. I’ve only been doing local, city driving, but I have had it as low 1-1/2 gallons. At that low level, it obviously sloshed and sucked air one time on a speed bump. The pump whined for 20 seconds and cleared. I consider 1 gallon empty anyway. If it gets to the pisses-me-off point, I’ll create a slosh pot or swap the tank. Any ideas for controlling slosh short of changing the tank are very welcome. Engineering a work-around seems to me to be a beneficial project given how many people find themselves in a similar position. Thanks for all the constructive feedback.
_________________
‘72 Karmann Ghia Conv.
‘73 Karmann Ghia Coupe
‘74 Karmann Ghia Coupe
‘70 Deluxe
‘72 Deluxe