Fuel return line and surge tank question/idea

datsun510 · Post by **datsun510** » Thu Nov 03, 2005 5:58 pm

Hi, I am currently building the fuel system for my efi project and am stuck. From what I understand, fuel starvation is going to be a problem with my relatively unbaffled tank. Some people with the same car as me have welded on wells, used surge tanks, etc... but I recently heard of someone using a fuel filter with a vapor return line fitting, like this:

tank> filter w/vapour return fitting> high pressure pump> injectors> regulator> return back into vapour fitting on filter

Would that have any effect on combating starvation or does this not make any sense? Would a large filter before the pump act as sort of an accumulator to feed the engine for say 1 or 2 seconds of surge? Any insight appreciated. Thanks,
Matt

lamrith · Post by **lamrith** » Thu Nov 03, 2005 8:55 pm

It was not that type of fuel filter, thought that one is interesting.

I used a full size spin on filter and bracket that was modified. IT also served to provide close to a GALLON of extra fuel for if the stock pump pulls a big bit of air or cavitates...

EFI fuel system upgrade

Jack · Post by **Jack** » Thu Nov 03, 2005 10:43 pm

Wow, that is a big tank. I used a 1 5/8 diameter pipe, nine inches deep for my surge tank. With the flow I see coming out of the fuel return, which goes back to the surge tank, I figure I have at least 5-6 seconds of fuel in reserve.

FYI - My surge tank has 4 fittings. The low pressure pump flows into the surge tank and overflows back to the gas tank. The high pressure pump curculates through the surge tank. All nipples, except the high pressure intake are at the top of the surge tank. The high pressure pump intake is off the bottom.

Jack

datsun510 · Post by **datsun510** » Fri Nov 04, 2005 1:10 pm

An issue I see with running the return straight into a surge tank is that heated fuel would be returning right back into the system. Is this really a problem?

What about using say that filter with 3 ports, putting the return on that vapour return, and running a "T" from that which goes straight to the tank? I guess the idea is that the fuel from the return line can both go to the tank, and to help feed the HP pump, trying to provide fuel for a brief surge. Sorry if this is a stupid question.. it would sorta look like this :

Code: Select all

               
                          Fuel tank
                        /          \
                   Feed          Return
                      |                ^
                      |                |
                      |                |
     filter->         |----------------| <-- T back to feed, before HP pump
                      |                |

Jack · Post by **Jack** » Fri Nov 04, 2005 3:07 pm

Not a stupid question at all. Consider though, that my low pressure pump will be constantly moving fuel from the main fuel tank through the surge tank, bringing in cool and taking some of the hot fuel back to the tank.

I felt the simplest, lowest risk method was to run two seperate fuel loops that happened to join up in the surge tank. I know the highest point in the surge tank is the return to the main tank, so all of the air will be purged, as it will be pushed out by the constant in-flow of fuel from the low pressure pump.

Jack