thread size of drain plug 55 nomad fuel tank?

[rockytopper R.I.P 5-13-2017]

Anybody know? I'm trying to buy a 90 degree barbed fitting online to install in bottom of tank for LS fuel pickup point for inline pump setup. I bought a straight barb fitting at Lowes last year and put it in my 4 door I sold but I don't recall what size pipe thread it had.
Thanks
Rocky

[chevynut]

It's a NPT pipe thread but I'm not sure which size. Other threads have said it's either 1/8" or 1/4". You should be able to tell just by looking at it because there's a big difference between 1/8" NPT and 1/4" NPT. Here's the NPT pipe ODs:

1/8 NPT .405"
1/4" NPT .540"

So if it looks like 3/8 bolt, it's a 1/8" NPT. If it looks like a 1/2" bolt it's 1/4 NPT. I read one place where someone said it looked like a 3/8 fine thread bolt.

[Rick_L]

Pretty sure it's 1/8" NPT. And too small for a fuel feed line.

[chevynut]

And too small for a fuel feed line.

Good point. Probably too small even if it was 1/4 NPT.

[rockytopper R.I.P 5-13-2017]

Thanks guys looks like I have to take a trip to Lowes again with a plug in hand. I have to disagree on the size not being big enough. Either 1/8 or 1/4 npt will work just fine for this application. Reason I say this is because the welbro 255 inline pump uses 5/16 barbed fittings. Also the GM filter regulator uses dormon quick disconnects and even the 3/8 feed id in that fitting is no bigger than the id of a 5/16 hose barb. I know this because I run the same setup on my cutlass. The main line running from reg to fuel rail will be 3/8 id high pressure. I have 50k on this setup with no issues. Reason I'm wanting to use the plug is to reduce the head on the pump they claim it is better on the pump. I plan to run the return back true the sender 5/16 line. The other option is to buy a sender with 3/8 feed and 5/16 return. I'm planning to add a large inline fuel filter as a pre filter/sump tank. I don't do this on my cutlass but thought it might help with fuel slosh starvation on empty tank.

[chevynut]

The nominal ID of a 1/8" NPT is 1/8" and the nominal ID of a 1/4" NPT is 1/4". In practice, they're usually a little larger than that.

No way will a standard 1/8" NPT fitting be large enough ID to work on an EFI fuel line, imo. I just measured the ID of a couple of 1/8" NPT fittings I have and they were both .187". You MIGHT be able to bore them to 1/4" which still isn't large enough imo.

1/4" NPT fittings are usually in the .280" ID range depending on the fitting...it could be reamed out too. The minimum recommendation for fuel line size for most EFI fuel systems is 3/8" or -6AN. A 1/4" NPT might work as a 3/8" fuel line is probably around .280" ID.

The problem is, your drain plug is 1/8" NPT. Maybe you can drill and re-tap it

I ran both my supply and return lines 3/8" stainless tubing with AN fittings. I'd rather not have any potential restrictions.

[chevynut]

Reason I'm wanting to use the plug is to reduce the head on the pump they claim it is better on the pump.

I'm not sure I understand that comment. What "plug" are you referring to? Seems like your pressure regulator is what determines the head on the pump. Too small of supply line will increase the pressure required at the pump.

[Rick_L]

C'nut, I think he's trying to have a positive head on the pump inlet (gravity feed), rather than suction. Which is good, but only when done right.

Rocky, don't put a filter in the suction line. It defeats the purpose of gravity feed. A coarse sock is the most you should use. Put the real filter on the pressure side of the pump.

[chevynut]

C'nut, I think he's trying to have a positive head on the pump inlet (gravity feed), rather than suction. Which is good, but only when done right.

We both know it doesn't matter if you take the fuel out of the bottom of the tank or out of the top of the tank with a pickup tube that goes to the bottom (siphon) if the pump is at the same level relative to the tank. The pressure at the pump inlet is going to be the same once that pickup tube is full. If it was me, I'd use a 3/8" stock replacement pickup and sender and plumb the pump to it.

[rockytopper R.I.P 5-13-2017]

We both know it doesn't matter if you take the fuel out of the bottom of the tank or out of the top of the tank with a pickup tube that goes to the bottom (siphon) if the pump is at the same level relative to the tank. The pressure at the pump inlet is going to be the same once that pickup tube is full. If it was me, I'd use a 3/8" stock replacement pickup and sender and plumb the pump to it.

C'nut I always thought that was correct myself as well.

Rick only reason I said pre filter is because if I used the drain plug hole there is no type of screen ie pickup shock. I was considering a 120 micron filter canister something like this. http://www.summitracing.com/parts/krc-4906bl/overview/ I believe it will gravity feed. Aeromotive recommends a 100 micron filter for pre suction side use. As you said the vet filter regulator is the real filter post pump it is rated at 5 microns I believe. I will reconsider using the sender unit for fuel injection. The drain plug just makes it easier to route to the rest of the fuel system. The 55 feed line runs down the passenger side but the LS engines feed on the drivers side. I was planning on mounting the fuel pump and regulator on the rear cross member or passenger frame next to the wheel well and then run high pressure compression fitting flex poly stainless jacketed line to the fuel rail along the drivers side frame.

What is the best source for buying an-6 pre length braided fuel line? I want to use it for connecting from the tank to the pump and filter regulator. Or do you just buy it and cut to length yourself? This is all on the low pressure side pre pump. Rockie question I know but I have never used it. My current setup accept for the main feed line from the pump uses all hose barb fittings and high pressure hose from local parts house. Works great and easy to replace but I want a cleaner look this go round.