The new motor for the Satellite is being treated to a new fuel tank to feed it, and i was thinking it should have a 3/8" line (in pace of the old 5/16" line). It's only ever had just the single feed line.
Fuel pump is a new mech one (not sure of the spec, it was specced by the engine builder). While looking into new lines I got to wondering if a return line is needed, and if so why? Is it mainly to return any vapour to the tank rather than unused fuel?
There's obviously differing opinions on t'web.
I don't necessarily want to complicate things if i don't have to, but if, as i have read, the combination of modern fuels and a mech fuel pump bolted to a hot engine, is likely to create issues with vapour lock then i'll look into it.
If it is a useful addition, does the return line run between the sender (back into the tank) and the filter after the pump?
TIA
Stuart.
Fuel Return Line?
Moderator: Moderators
Re: Fuel Return Line?
Hi Stuart. I would say do it. With a single line my 440 would regularly conk out in heavy traffic but fitting a new filter with a return outlet for vapour and a line back to the tank solved the issue. For some reason the previous 383 never had a problem...
Re: Fuel Return Line?
From memory (translation - need someone to confirm 
)....
the vapour purge is a nice-to-have-advantage but not the main reason. It comes down to fuel pressure regulation. If a fuel pump has a fixed delivery (such as old style electrical pump), the pump is trying to supply more than you need most of the time, and the actual fuel supply is being regulated either by the needle valves / floats in the carb or by a pressure regulator (I'm ignoring fuel injection for now) So the fuel is pushing against a dead end some of the time. Mechanical pumps don't mind doing this (dead heading) (plus they are variable to a degree) but electrical don't really like that - hence fitting a regulator with a return line - effectively a bypass. That's the reason for a return line. With a mechanical pump like you have, you don't need the return line cos the pump is happy dead heading. You might still need a regulator if you have a high pressure pump and the pressure is higher that the carb needle valves are spec'd for, plus it is decent practice to have a regulator. If you do fit one, you can just get one with a bypass making it pretty simple to fit a return line and yes you could get the benefit of sending some vapour back to the tank. In your case I'd say not a tremendous amount of work to fit one, for not a tremendous benefit.....
)....the vapour purge is a nice-to-have-advantage but not the main reason. It comes down to fuel pressure regulation. If a fuel pump has a fixed delivery (such as old style electrical pump), the pump is trying to supply more than you need most of the time, and the actual fuel supply is being regulated either by the needle valves / floats in the carb or by a pressure regulator (I'm ignoring fuel injection for now) So the fuel is pushing against a dead end some of the time. Mechanical pumps don't mind doing this (dead heading) (plus they are variable to a degree) but electrical don't really like that - hence fitting a regulator with a return line - effectively a bypass. That's the reason for a return line. With a mechanical pump like you have, you don't need the return line cos the pump is happy dead heading. You might still need a regulator if you have a high pressure pump and the pressure is higher that the carb needle valves are spec'd for, plus it is decent practice to have a regulator. If you do fit one, you can just get one with a bypass making it pretty simple to fit a return line and yes you could get the benefit of sending some vapour back to the tank. In your case I'd say not a tremendous amount of work to fit one, for not a tremendous benefit.....
Gavin Chisholm - 414ci W2 Stroker SmallBlock Panther Pink '71 Challenger convertible - in bits
Car progress can be viewed here
Car progress can be viewed here
Re: Fuel Return Line?
with a bigger line you need to consider if the weight of the fuel in it will have an impact on a remotely mounted mechanical pump with an inlet a few inches below the outlet level of the tank. It is basically fed by gravity, your acceleration will try to make fuel in the line stand still or run back.
the fatter the pipe the worse that gets
mechanical pumps do not suck
very few fuel pumps do, which is why the electric ones work best mounted under the tank and therefore can handle great big fat lines right up to the front of the car. 25-50 PSI output of an electric pump is not going to be bothered by a 0-60 of 6-10 seconds with a fuel line bore upgrade.
a mechanical pump 2-3 meters away that has no ability to suck might, the valves in it are neoprene rubber designed to block off a chamber as the pump tries to push not combat the effects of "suck" whilst they are open and as the fuel tries to run back down the line to the tank.
Dave
the fatter the pipe the worse that gets
mechanical pumps do not suck
very few fuel pumps do, which is why the electric ones work best mounted under the tank and therefore can handle great big fat lines right up to the front of the car. 25-50 PSI output of an electric pump is not going to be bothered by a 0-60 of 6-10 seconds with a fuel line bore upgrade.
a mechanical pump 2-3 meters away that has no ability to suck might, the valves in it are neoprene rubber designed to block off a chamber as the pump tries to push not combat the effects of "suck" whilst they are open and as the fuel tries to run back down the line to the tank.
Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
Re: Fuel Return Line?
I've run a fuel vapour separator and a fuel return for a few years now, no more bogging down in traffic on a sunny day, it helps keeps cool fuel at the carb all of the time.
Are we there yet dad ..... 10 to the gallon but worth it.
MMA Public Relations Officer.
MMA South London and Surrey Area Rep.
MMA Public Relations Officer.
MMA South London and Surrey Area Rep.