Fuel line size and fuel filter questions
 

I am helping a friend put in his freshly rebuilt procharged 502. The engine builder wants -10 line from the tank to the fuel pump and -8 from the pump to the regulator. Problem is I removed the tank pick-up and it's only a 3/8" pipe thread bung welded into the tank. I would think that would be okay going to -8 line but going to -10 seems pointless as the bottleneck will be at the pick-up. Or am I off on this logic?

Also, his boat currently has 2 aeromotive in-line filters. Is two necessary? I am sure it's helpful but the way it's ran it will be a huge pain to convert over to larger line.

Aeromotive recommends two filters, one before the fuel pump and one after, but the filter before the pump is a large micron filter. IMO a good setup has the filter screw right to the intake of the pump.

I think you could still benefit some by having the larger fuel line, even if you do have a small bottleneck at the pickup. How far away from the pickup is the fuel pump going to be (or better stated, how long is the larger gas line going to be)?

Got ya on the fuel filters. That is exactly what he has, one filter before the pump and one after, so I will leave it.

The pump is about 18"-24" from the pick-up. I agree that going to -8 is needed but I don't see the point of -10 when the pick-up is only 3/8"???

you do not want to restrist inlet in any way do the -10 trust us its worth it i know you are down at the fitting but after that let it flow just do young grass hopper

Decided to wait and talk to the engine builder and he agreed -10 is pointless with a 3/8" pick-up. So, now we have to get a larger pick-up in the tank somehow.

can you block it off, and is there a inspection plate next to it that you could take off and have a bigger pick up installed. mine had two plates but I unscrewed my pick up went to larger one then the 10 to 8s to 6s on the dom. other wise empty the tank fill with water cut and have new one welded in drain tank and dry out or put 10gals in then pump out. good luck

No inspection plate but there is a plate for the sending unit. I talked with the builder again and he said if we can get it to 1/2" ID that should be good. So, I'm going to try to find a way to weld a pick-up tube to a 3/8" pipe thread fitting that is drilled out to 1/2" ID. If that doesn't work I'll let the builder figure it out when we take the boat down there. Free drinks only buys so much of my labor. LOL

Is the tank aluminum???




Here is a option your tank bung is Welded right?

This is what I did.

If it is A 3/8 female pipe thread. that is welded. Get a male
3/8NPT brass close nipple. I went to my local hobby shop and got 15\32 brass thin wall tubes which fit perfecly into a 3/8 brass nipple. Soldered them together.
These are about 14 inches long and slide into my existing tank
bungs. The close nipple on the top threads into existing tank bung. The other end of the 3/8 sticks out of tank allowing
the hookups.
These are now my pickups and it allows me to still utilize the tank bungs ( no tank modifications) and 1\32 under a 1/2 inch pickup.

Hope this helps
Gerry

Excellent idea. Thanks.

what kinda power is this motor making

715hp

Fuel Line Size
 

With a 715 hp engine you will need a wide open throttle .99 GPM. That is a bunch to try to suck through a 3/8 Inch pick up.
I would look to a gas tank repair company to install a larger bung in the tank. I would think this is a lot cheaper in the long run than replacing the fuel pump and possibly a engine.

Put a new 3/4 inch NPT bung in the tank and run #10 line minimum to the pump suction. Check the flow ratings of the filters. Take the anti siphon valve out. It is way to restrictive. Pumps don't suck fluid in, they push fluid out. Atmospheric pressure pushes the fluid while the pump inlet cavity forms a slight vacuum. Do not restrict the inlet.

I agree that is why I was trying to get it to 1/2". The builder said that would be sufficient. At this point I think I will just let him do it.

Should have taken your advice earlier but we don't have any hobby shops. Called one 50 miles away and they have 17/32" which I can fit in a relieved 3/8 pipe fitting and give me a hair over 1/2". Thanks for the tip!

I think mcmaster-carr has brass thinwall tubing.

Dont forget to cut the new pickup tube at a 45 at the lowest point
with some side cuts.


Gerry