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return pipe
Posted: Sun Oct 04, 2009 9:31 am
by bones
Hi all, what size should the fuel return pipe be, main feed is 3/8, can the retun pipe be 5/16 or a 1/4" i/d.
rich
Posted: Sun Oct 04, 2009 4:28 pm
by Ian Anderson
Should be the same size as the flow
At Idle almost all of the fuel will be returning to the tank
By reducing the pipe size you may accidentally increase the pressure in the system above what the regualtor is trying to set
Cheers
Ian
Posted: Sun Oct 04, 2009 6:39 pm
by mgbv8
Is this for a carb setup Rich ?
Posted: Sun Oct 04, 2009 7:02 pm
by bones
yes a carb set up, its on my brothers motor, a holley 600 d/p,
rich
Posted: Sun Oct 04, 2009 7:32 pm
by mgbv8
You need to think about the delivery pressure required Rich!!
And how much the pump can flow as well.
If the return line is too big, you will have low pressure at the carb.
Does the pump have a regulator fitted to keep pressure down to the right level ??
The Holley wants about 5-6 psi doesnt it??
I would think about fitting a Tee just before the carb, and fitting a restrictor in the return line.
I had this issue on my nitrous fuel system. The regulator did not like being dead headed. And it gave me fluctuating fuel pressure off the line. I put a plastic fuel Tee in just before the solenoids and found an old carb jet with a 2mm hole that fitted just right into the plastic Tee. I also fitted a glass fuel filter in the return line so I could see what was happening. The 2mm hole is enough to get a good flow back to the tank so the regulator can control properly. And my fuel pressure during a run is stable now.
Pel
Posted: Sun Oct 04, 2009 7:39 pm
by topcatcustom
Do you need a return on a carb or is it because you are running a mech pump?
Posted: Sun Oct 04, 2009 7:53 pm
by mgbv8
Depends on what fuel pump you are running Tom. If you use a high pressure pump via a regulator. A return line is a good idea to stop the regulator getting stroppy.
Posted: Sun Oct 04, 2009 8:04 pm
by stevieturbo
More than likely the 5/16" return will be fine. I wouldnt drop as low as 1/4, although a lot depends on pump flow
Posted: Sun Oct 04, 2009 9:37 pm
by bones
its an electric fuel pump, 140gph i think, hes got a nos fogger direct port system fitted ,and regulator, so 5/16 return will be ok then??
Posted: Sun Oct 04, 2009 9:46 pm
by stevieturbo
140gph is a hell of a lot. Id sooner use a 5/16 feed and 3/8 return
Posted: Sun Oct 04, 2009 10:03 pm
by bones
the pump could be the 125gph it flows 110gph at 7psi, the engine is a 360 mopar 420bhp, the pump has got 3/8 ports.
rich
Posted: Sun Oct 04, 2009 10:04 pm
by stevieturbo
then just use 3/8 feed and return
Posted: Sun Oct 04, 2009 10:30 pm
by bones
Ok thanks for the replies, i will let him know.
rich