| [ Total Views: 2915 | Total Replies: 27 | Thread Id: 54421 ] |
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 gerrelt
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| posted on July 18th, 2006 at 05:28 AM |
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fuel return line...
I am converting my 73 1303 (super) beetle to a watercooled Alfa Romeo boxer engine.
This engine has fuel-injection (Weber IAW). Now I am going to install the fuel lines. I was thinking of this setup, but I am wondering if it will
work, feel free to comment on it:
Note the 6 mm outlet of the tank. My tank has a welded on 6 mm outlet which isn't easy to change to 8 mm (or higher).
Let me hear what you think.
Greetings,
Gerrelt.
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ricola
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| posted on July 18th, 2006 at 07:01 AM |
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On light throttle you will circulate hot fuel which will hurt performance, you also risk trapping air in the 'closed' circuit.
You will probably get away with the 6mm outlet your engine, but I would fit the return somewhere else, maybe into the filler neck..
Rich
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Stanley
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| posted on July 18th, 2006 at 07:06 AM |
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I think the 6mm line at the tank will cause a restriction regardless of line size upstream.
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 vw54
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| posted on July 18th, 2006 at 07:11 AM |
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Run 8mm new rubber lines from front to rear no probs put them inside the tunnel
Also increase the outlet size out of the tank, to the LP filter and pump 12 or 13 mm would be good find another tank if the outlet has been welded in
and as per above run the return line to the filler neck in 8mm
whats the Pulse Damper do ????
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Stanley
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| posted on July 18th, 2006 at 07:27 AM |
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Pulse damper, from what I know, takes out the pressure spikes caused by the injectors. Kinda like fitting an accumulator to your water tap to take out
water hammers
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gerrelt
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| posted on July 18th, 2006 at 07:29 AM |
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| Quote: | Originally
posted by ricola
On light throttle you will circulate hot fuel which will hurt performance, you also risk trapping air in the 'closed' circuit.
You will probably get away with the 6mm outlet your engine, but I would fit the return somewhere else, maybe into the filler neck..
Rich
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I use copper fuel lines attached to the underside of the heater channels:
So I think the fuel will be cooled while driving, but when standing still (like in a traffic jam) this could be a big problem.
If I use the Y construction, the 6 mm outlet can't be much of a problem, because the outlet only has to provide the used fuel. The circulated fuel
will be added downstream (at the Y). Given the fact that the Alfa engine uses less fuel than the beetle engine, the 6 mm outlet should be OK.
But, like you said, I am still worried about heating up the fuel and trapping air is also a concern.
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gerrelt
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| posted on July 18th, 2006 at 07:32 AM |
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| Quote: | Originally
posted by Stanley
Pulse damper, from what I know, takes out the pressure spikes caused by the injectors. Kinda like fitting an accumulator to your water tap to take out
water hammers
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Exactly! It's probably not the officaul term for this part, but English is not my native language so these autoparts specific words are quite
difficult sometimes... :-)
[ Edited on 17/7/2006 by gerrelt ]
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gerrelt
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| posted on July 18th, 2006 at 07:36 AM |
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| Quote: | Also increase the
outlet size out of the tank, to the LP filter and pump 12 or 13 mm would be good find another tank if the outlet has been welded in
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Yep, that's the problem, the outlet is welded in. And there is no standard super beetle tank that has a bigger outlet than 8 mm. There are fuel
injected super beetles, but they have 6 or 8 mm (don't know) outlets. They do have a return line.
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vw54
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| posted on July 18th, 2006 at 07:38 AM |
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Nuthing wrong with those fuel lines
What throttle body are you using
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gerrelt
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| posted on July 18th, 2006 at 07:47 AM |
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| Quote: | Originally
posted by vw54
Nuthing wrong with those fuel lines
What throttle body are you using
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The one that came with the engine. The engine is originally equiped with fuel injection (Weber IAW).
The throttlebody is the thing the throttle calbe attaches too, right? Than it is partially visible in this picture:
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GeorgeL
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| posted on July 18th, 2006 at 08:12 AM |
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Remember that 6mm isn't just a little smaller than 8mm. The cross-sectonal area is about half as much, which might be a problem if fuel is sent back
to the tank. Even though the engine gets better mileage, the flow through the pump will be several times the consumption of the engine.
The best approach is to have correct fittings brazed onto the tank. All appropriate precautions relating to welding fuel tanks apply of course. I'd
braze NPT nuts onto the bottom of the tank so that you can swap outlets as needed.
If you would rather not do that, then you could run a fuel header tank as recommended by the SDS EFI folks. You need a 1 liter or so tank with two
fitting on top and two fittings on the bottom. Feed one of the lower fittings from the tank through an ordinary low pressure electric fuel pump. One
of the upper fittings is used to return fuel to the tank via the filler vent. The other lower fitting feeds the high pressure EFI pump, and the other
upper fitting takes the EFI return. Size the fittings appropriately to match the tank outlet, etc.
This way, the fuel stays cool because it is being recirculated to the tank, but the capacity of the 6mm outlet isn't being exceeded. If you
temporarily exceed the capacity of the 6mm outlet, the level in the header tank drops to satisfy the engine's need for fuel flow.
It's kind of Rube Goldberg, but this would get you around the need to braze the tank.
Untried, but also a viable idea would be to put a heat exchanger in the return line for your "Y" arrangement. Heck, even your long return line
might provide enough heat exchange to do the trick. I don't know what this setup would do with air bubbles, though.
George
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Baja Wes
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| posted on July 18th, 2006 at 09:07 AM |
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There are a few problems. The hot fuel recirculating will definitely be a problem, trust me, I had a similar set-up with a surge tank where your Y
piece is, and it overheated the fuel recirculating. It looked like this;
You may want to read this thread;
http://forums.aussieveedubbers.com/viewtopic.php?tid=9938
Also, never ever put a fuel filter before a high pressure pump. It will cause cavitation in the pump which will damage it. You should only ever use a
strainer on the suction side of a HP pump (like a mesh).
You need to do what others have mentioned and add a small surge tank. You can then use a LP pump to recirculate the fuel back to the main tank, you
can then use your 6mm outlet and return to the filler neck or similar. My current set-up looks like this;
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pete wood
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| posted on July 18th, 2006 at 10:32 AM |
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sorry to tell you this, but with vibration copper work hardens and becomes brittle over a period of time. Eventually it splits and I think you can
imagine what happens. You'd have been better using rubber fuel line than that. When the car is finished and you have some money, pic up some
stainless steel or aluminium high pressure pipe in the same diameter and replace those lines.
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vw54
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| posted on July 18th, 2006 at 11:26 AM |
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| Quote: |
Also, never ever put a fuel filter before a high pressure pump.
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Wes Volkswagen and Audi use a Low pressure Plastic fuel filter on all the cars ive seen
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bajachris88
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| posted on July 18th, 2006 at 11:32 AM |
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| Quote: | Originally
posted by pete wood
sorry to tell you this, but with vibration copper work hardens and becomes brittle over a period of time. Eventually it splits and I think you can
imagine what happens. You'd have been better using rubber fuel line than that. When the car is finished and you have some money, pic up some
stainless steel or aluminium high pressure pipe in the same diameter and replace those lines.
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maybe rubber rings over the lines where the lines mount on to might help to lower and soften the vibs..
(ô_!_/ô) (ô_!_/ô)
69' baja: kombi box, thing spindles, irs, disc front, type 3 rear drums, 2 inch lift kit, 31x10 rears. 
New engine in process: 94mm p&bs, 74mm C/w chomol Crank, 35.5x39 SP heads, turbo. Wierd combo, hopeful torque monsta! |
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RENNWAGEN
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| posted on July 18th, 2006 at 12:05 PM |
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Maybe rubber rings would help but for the price of some aluminium fuel pipe I wouldn't risk it. I looked into copper early on and came across some
horror stories. If those fuel lines crack while driving any leakage could be blown back to the hot end.
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Baja Wes
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| posted on July 18th, 2006 at 12:35 PM |
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| Quote: | Wes Volkswagen and
Audi use a Low pressure Plastic fuel filter on all the cars ive seen
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Dave,
Is that on EFI cars before a HP EFI pump? I haven't seen any cars like that, but haven't looked that much either.
What sort of filter medium does the plastic Audi/VW fuel filters have? I'd expect them to be a mesh type. The cardboard filter medium type filters
you buy for carby engines are too restrictive for most HP pumps.
And not all HP are the same. The positive displacement type ones would handle a restriction on the suction side better than the turbine style
pumps.
All the EFI cars I've seen run a strainer bag in the tank. I've seen one suby powered conversion with a carby fuel filter on the inlet to the HP
pump, and you could hear it cavitating away.
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pete wood
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| posted on July 18th, 2006 at 02:13 PM |
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woah, hold on a minute.
this is my setup, do you think there could be a problem there?
tank --> generic fuel filter --> facet low pres pump --> surge tank --> hi pres pump --> EFI fuel filter --> motor.
Should I put the generic filter after the facet pump?
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Baja Wes
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| posted on July 18th, 2006 at 03:44 PM |
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A facet pump is positive displacement and isn't as sensitive to inlet restrictions as HP pumps. It won't care too much.
I run a rebuildable mesh strainer on the suction to my facet pump. You buy them from autobarn or anywhere, it's a little mesh screen. Just enough to
keep the rust flakes from the tank out of the facet. The facet has a magnet in the main mechanism, and it attracts the rust flakes. They then build-up
inside and make the sliding piston part seize (I know from experience  ).
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gerrelt
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| posted on July 18th, 2006 at 08:32 PM |
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| Quote: | Originally
posted by RENNWAGEN
Maybe rubber rings would help but for the price of some aluminium fuel pipe I wouldn't risk it. I looked into copper early on and came across some
horror stories. If those fuel lines crack while driving any leakage could be blown back to the hot end.
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Yep, I use rubber rings.
I used a peice of 8 mm rubber fuel hose around the copper line, and around the hose the clamp is fitted. The clamp is attached to the car.
These copper lines I use are originally intended for gas (= not fuel, but the stuff you cook your diner with) lines in campers and caravans. They are
soft and can be bend by hand.
I can't imagine they would sell gas-lines that would crack easily for campers/caravans. The consequences would be quite severe.
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vw54
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| posted on July 19th, 2006 at 11:27 AM |
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Yeah Wes
They appear to be the hard type plastic not the soft stuff used on carby engines and the filter looks like a paper type substance not metal mesh. I
had this on the Audi 5+5 straight out of the tank and into a plastic type fileter then into the HP pump and into a HP steel type filter
Same as the 76 Bay window Kombis
the copper will work harden thats why your not allowed to make brake line out of it. Replace them with rubber flex hose its about $50.00 for 8
meters from Pirtek
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richbaker78
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| posted on July 21st, 2006 at 06:20 PM |
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when I first read about the copper hardening I presumed it was some reaction with petrol - ive never heard of this with brakes too....
here in the Uk its acceptable and legal to have copper brake lines - in fact it is considered preferable by some....and many kits are sold in copper
by automec and similar. ive never come across this being a bad thing to do. Im interested to hear more bout this work hardening of copper as I have
copper lines on both my van and my morris minor!! why does it harden? is it a reaction with certain fluids?
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mackaymanx
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| posted on July 21st, 2006 at 07:07 PM |
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As you work a metal like Cu it hardens. Vibration of the fuel line or pulsations from the pump will cause this hardeneing of the line. As the
hardening progresses strenght increases as does brittless (you can see this difference in hard drawn compared to soft drawn Cu pipe). Work hardening
is a mechanical process, put some soft Cu pipe in a vice and bend in back and forth. Its easy at first but gets hards as you go, until the pipe just
breaks in half.
[ Edited on 21-7-2006 by mackaymanx ]
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ElusiveStranger
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| posted on July 25th, 2006 at 07:12 AM |
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Dunno if you guys are interested but there's pictures of my modified '78 Bay tank (and some of my conversion) here:
http://www.vwkd.co.uk/bb/viewtopic.php?t=228
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ricola
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| posted on July 25th, 2006 at 05:00 PM |
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Rich,
Brake line in the UK is made of CuproNickel, the nickel content makes a big difference to its strength and resistance to work hardening..
Rich
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gerrelt
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| posted on August 10th, 2006 at 04:15 AM |
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I did a test with my copper tubing. I put a piece of it in a vice and then bent it all directions. It didn't crack.
I had to really clamp it in the vice because it came out. This flattenend the end of it. And, after a lot of bending
it back and fort it finally broke.
My gut feeling says it broke a little earlier than an iron pipe would. But it took a LOT of bending to get it to break.
It was a lot more bending than what these pipes would endure when mounted under a car.
Add to this that these pipes are sold as gas-lines (the stuff you cook with, not the fuel) for campers and
caravans. Campers and caravans vibrate a lot, I can't imagine that these lines would be allowed to use as
gas-lines when they have a habbit of breaking.
Now, my project. I finally decided on this setup:
The pump should always have enough fuel because the 6mm tank outlet only has to provide the used fuel. Which
should be even less then with the original VW engine.
The only problem which could be encountered is fuel
warming up. But, the fuel doesn't spent much time around the engine, so it doesn't really get the change to
warm up (the fuel rail is also isolated with rubber). Furthermore, my copper fuel lines will act as coolers.
But I will monitor the temperature.
This is how it looks like in the nose of my beetle:
As you can see it's easy to check for hot fuel, I just have to open the front decklid and feel the 22 mm pipe.
Some more text and another picture on this site.
More text an pictures on my fuel lines here.
Thanks for all your thoughts and suggestions.:thumb
Greetings,
Gerrelt.
[ Edited on 9/8/2006 by gerrelt ]
[ Edited on 9/8/2006 by gerrelt ]
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vw54
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| posted on August 10th, 2006 at 07:02 AM |
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Copper work hardens over time ... it dosent have to bend as you have done in your testing precudures
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Baja Wes
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| posted on August 10th, 2006 at 08:18 AM |
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Gerrelt,
At my first attempt, I ran almost the same set-up as what you have shown there, but I had a surge tank where you have the 22mm pipe. It looked like
this;
It didn't work. After about 40 minutes the engine would start cutting out because the fuel going around and around got too hot. I think without a
surge tank you will notice this problem earlier.
That's my experience anyway...
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