PDA

View Full Version : Fuel tank return - in top of tank or bottom of tank below fuel level?



LINCOLN
30-09-11, 11:32 AM
Two 044 pump EFI car with magnafuel reg with - 8 to and -8 from engine.

Can I return the fuel from the reg to the bottom of the tank? Makes it easy as then there are no fuel lines in the car. I could weld a tube in the bottom to return above the fuel level.

Thanks.

LINCOLN
30-09-11, 11:34 AM
Is the head pressure is the only thing I have to worry about if I return to the bottom - tank is only 250mm deep.

gmh265
30-09-11, 12:54 PM
There is fuck all head pressure in a 250mm deep fuel tank.. factory fuel systems normally return to the bottom of the 'sump' inside the tank that the factory pump picks up from.

LINCOLN
30-09-11, 02:53 PM
Thanks.

Do factory tanks return in the top of the tank with a tube inside down to the bottom? Or is the fitting on the bottom of the tank?

Mr Ed
30-09-11, 03:06 PM
Head pressure from a 250mm deep tank would be the same as bending the hose upward 250mm anyway so no difference, especially when compared to the high point in the system.

Most factory setups Ive worked on return in the top through the inspection plate and the tube only pokes through a inch or two, no idea if this necessary though.

number8
30-09-11, 03:13 PM
keeping return away from the pickup is better imho as you avoid repeated looping of the same fuel / fuel heating as much as possible

edit: like this
http://farm7.static.flickr.com/6155/6196624895_20f1c13120_b.jpg

Mr Ed
30-09-11, 03:52 PM
Your main feed line in that pic, have you just drilled a new drain point in through the base of the tank? Did you put any baffling in?

Curious as doing something like that in mine would be far simpler (therefore better) than using a lift pump and fucking around with surge tanks/etc.

mopar lover
30-09-11, 03:53 PM
keeping return away from the pickup is better imho as you avoid repeated looping of the same fuel / fuel heating as much as possible

edit: like this
http://farm7.static.flickr.com/6155/6196624895_20f1c13120_b.jpg

Keep the return away from the pickup when you are returning from the top because you are aerating the fuel and that can cause the pump to cavitate, cavitation kills pumps.

LINCOLN
30-09-11, 04:11 PM
Thanks for all the replies.

I am thinking of returning into the bottom of one of the outer "sumps" that one of the carters draw from. This photo shows the tank upside down.

http://i147.photobucket.com/albums/r308/lincolno/IMG_0297.jpg

Each left and right carter feed an internal swirl pot that feeds back to the left and right sumps via internal tubes.

http://i147.photobucket.com/albums/r308/lincolno/IMG_0300.jpg

This photo is the tank from above - those holes left and right gravity feed the sumps.

Mr Ed
30-09-11, 04:16 PM
Id have the return designed so the fuel returning will be the last to go back to the pumps. Keeps the fuel as cool as possible, and its not like youre going to be lacking flow to those sumps!

number8
30-09-11, 05:56 PM
Your main feed line in that pic, have you just drilled a new drain point in through the base of the tank? Did you put any baffling in?

Curious as doing something like that in mine would be far simpler (therefore better) than using a lift pump and fucking around with surge tanks/etc.
you might be ok, depends how much fuel youre pulling out.

theres a white plastic container inside the jza80 fuel tank which serves as sort of a surge tank. from memory its approx the size of a 4L icecream container, with holes around the bottom to let the fuel in. on mine the pickup is in the middle of this, which does a fairly good job of keeping fuel up to it

its not ideal though, even with the pump controller on low speed, the flow rate of that pump sucks the container dry if the fuel level gets below the top of the container. this used to occur when fuel dropped to somewhere around 1/5 of a tank. this would happen over the timespan of sitting at a set of lights, without movement or sloshing helping the refill, start driving along and it would be ok again. i thought about increasing the number of holes it has around the base to help this but decided it wasnt ideal. i prob could also drop the low mode pump speed some more but thats not really a proper fix either.

in retrospect i would go to a sheetmetal tank with a distinct low point for the pickup, with provision for twin exhausts running alongside the transmission and straight out the back each side of the dif, instead of a single bigger pipe which scrapes on everything. and/or a mech pump with an 044 or two feeding a header tank. having several litres of fuel in the engine bay is significant discouragement though.


I am thinking of returning into the bottom of one of the outer "sumps" that one of the carters draw from..if im understanding you right, at idle youre going to be returning the same fuel over and over. i dont think this is a good idea.

Mr Ed
30-09-11, 10:55 PM
Found this blokes method for pick-up/baffles, looks interesting.....Ive got an A1000 too, didnt think using it in-tank was an option.

http://i301.photobucket.com/albums/nn71/65svtfastback/EFI%20tank/efitank028.jpg

Momus
02-10-11, 04:58 AM
Two 044 pump EFI car with magnafuel reg with - 8 to and -8 from engine.

Can I return the fuel from the reg to the bottom of the tank? Makes it easy as then there are no fuel lines in the car. I could weld a tube in the bottom to return above the fuel level.

Thanks.

Return to the surge tank below the fuel level.
You won't be troubled by hot fuel and can be assured that if the lift pump situation is ever marginal- hot day, low volts, low fuel, that your chances of starvation are minimised.
Returning the fuel below level in the tank is usual practice to minimise the evaporation of the lighter hydrocarbon fractions.

LINCOLN
03-10-11, 11:21 AM
Thanks all for the answers. Will return to one of the outer sumps that feed the central surge tank.