Fuel system: Sending Unit Question

[davamor]

Good day, everyone,

I'm a little new to the forum so first I want to offer my apologies if I violate any forum etiquette. Navigating the forum has proved more challenging at times than completing the build. :-)

My build is a Mk4 roadster and I’m at the point where I’m building the fuel system. The kit came with 5/16” supply lines and a fuel sending unit that has a 5/16” sending line and ¼” return inlet.

My engine is a 347 cu small block that is rated at about 425 hp. Everything I’ve read says that the 5/16” kit lines won’t be sufficient for that engine. The engine came with the correct lines, pumps, filters, fittings, etc, so I'm set there, but I’m having trouble finding a replacement sending unit with ⅜” plumbing. There are plenty of sending units on the market, but I'm not sure how to tell if what I'm buying will fit the kit fuel tank (opening diameter, depth, etc).

Has anyone encountered this or know of a suitable sending unit and where to pick one up?

Thanks.

Dave

[rich grsc]

Your 5/16" pump is adequate for your engine, especially if you have 3/8" hose.

[davamor]

Thanks, Rich. My question was on the sending unit. The sending pipe out of the tank is 5/16". Are you saying that is adequate if I use the larger lines that came with the engine? I'm also concerned about the 1/4" return inlet pipe. Will that be sufficient? I don't want that small diameter back to the tank to degrade the system's performance. I'm definitely a newbie to fuel systems. Any insight on this would be appreciated.

[Papa]

My recommendation is this if you're doing an in-tank fuel pump.

https://www.promracing.com/high-flow-fuel-pump-hanger-for-1986-1997-mustangs.html

[rich grsc]

There isn't a sending unit on the tank, so I guess you mean the fuel pump hanger. Yes it will work fine, it's not really necessary to change it, the resistance to flow is more of an issue with the hose. Think of how water flowing through a garden hose gets slower the longer the hose. Get a larger diameter hose and you get more flow, even though you didn't change the shut off valve. No harm in changing the pump hanger, except to your wallet.:rolleyes:

[Papa]

Davamore: A more correct term is fuel pickup for external pumps or pump hanger for in-tank pumps. The sending unit is for the fuel gauge. In some cases, the two can be combined into a single fixture. The complete kit ships with a pickup and a separate sending unit. If you haven't considered the advantages of an internal fuel pump, just ask how many modern cars have external fuel pumps these days. ;)