21 replies to this topic

[76lxhatch]

You could; that particular connection has an internal tube which runs along the top inside all the way to the back of the tank so it works when facing downhill. The other two in each front corner of the tank are exactly as they appear and work when facing uphill/deal with side to side fuel movement. You could re-purpose any of these for a return line, as long as you are happy that you will still have adequate breathing with the remaining connections.

[V-SLR5000-P]

Return line should be at least as big as the delivery line to avoid pressure on the return side. Breather may be too small?

[Oversteer]

EFI setup ??

 

Tank/pickup isn't designed for a EFI pump and return, should be running an external surge to avoid pump sucking air....doesn't have to be big, you could get away with .5-1L for a stock 305 type engine.

[ls2lxhatch]

You drill a hole and fit a bulkhead fitting either through the sender plate or through the tank next to the sender hole. Another option to drill and solder a return line into the sender plate.

 

 

You can put a tee in the filler neck breather for the return line. There may be room to run the return line over the top of the tank in the crease to get to the filler.

 

Picture from this thread.

 

Edited by ls2lxhatch, 04 January 2016 - 10:14 PM.

[76lxhatch]

Just been looking at info on return line sizes for my EFI conversion, I will be running a smaller return line and having seen a lot of recommendations to follow an old rule of of thumb about having the return at least as big as the feed I was starting to second-guess myself. However I think that's overly simplistic approach and came to the following conclusions after a bit of reading:

 

1) obviously the return line needs to be big enough to return enough fuel to avoid pressure spikes as V-SLR5000-P mentioned, but

 

2) the return is often a size smaller than the feed (very common in OEM applications) because at lower pressure you get a higher flow rate back to the tank. Having the return line too large can actually cause the pressure to pulse excessively if the pressure drop is too great, i.e. pressure may drop too far too quickly as the regulator opens - its effectively vacuuming the fuel out of the high pressure side of the system

 

3) high pressure fuel system (EFI) return lines can generally get away with being slightly smaller than low pressure systems, since there is a much greater pressure drop. e.g. a highly unlikely scenario but if you had 20psi in the return line this is still enough of a drop to maintain 43psi in the rail for EFI, but a major problem if you want 7psi for a carb

 

4) to decide on your line sizes you need to know how much your fuel pump and feed line combination flows, the smallest return line (with a bit of overhead/room for changes) that supports this flow while maintaining return line pressure under ~3psi is the go for stable pressure regulating

 

I'm also not a fan of having huge 1/2" lines running under the car if its not necessary. Carb and EFI return lines follow exactly the same principle, its just that carbs run at lower pressure so you have less tolerance for increased return pressure, but potentially more tolerance for pressure fluctuations depending on the bowl setup.

[ls2lxhatch]

The Ryco Hose Size Selection Nomograph is a good guide to selecting the required hose or tube bore size/inside diameter.

Keep in mind that hose is measured by bore size/inside diameter and tube is measured by outside diameter. This is so that a 3/8" hose will fit over a 3/8" tube.

3/8" (9.5 mm) hose has a bore size/inside diameter of 3/8" (9.5 mm).

3/8" (9.5 mm) tube has an outside diameter of 3/8" (9.5 mm). The bore size/inside diameter of the tube is calculated by subtracting the wall thickness of the tube. 3/8" (9.5 mm) aluminium tube will typically have a wall thickness of around 1 mm which gives an bore size/inside diameter of around 7.5 mm
 

[76lxhatch]

God speed flow 200 series black hose 5 meters 1/2 inch cost me $300 bang

 

Eh? Surely you can get bundy cheaper than that, and why do you need 1/2"?
 

[Statler]

Yeah I think I will use that as return as it is close to 3/8 . And I'll get someone to modify my pickup to a 3/8 pipe and run a 1/2 all the way .. God speed flow 200 series black hose 5 meters 1/2 inch cost me $300 bang

I am well over $1500 for lines & fittings. lol.

 

If i was doing it over i would have used hard lines instead.