Fuel tank confusion...

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steveo
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Fuel tank confusion...

Post by steveo » 20 Mar 2020, 17:38

I'm working on my fuel tank, and so far everything's going OK, but now I'm trying to connect my fuel tank to the world and I'm just getting confused. You never really think about fuel tanks. You put stuff in, you burn it, you put more stuff in, and occasionally it lies to you about how much stuff is in there! Having to actually work out how to connect one to the world is fizzing my brain so I could use some guidance from the community!

I have built my tank out of 16 gauge 316L stainless. It will have the following connections:

a) Fuel out: This will be connected to an in-tank fuel pump and then onto the EFI system
b) Fuel return: What doesn't get burnt gets sent back so it has to have someway in
c) Breather pipe: Living in AZ there's a fair amount of expansion due to heat, and for fuel filling purposes these are a good thing.\
This will be connected to the breather on the Miata filler neck
d) Fuel in: A 2" (or so) stainless tube connected via a hose to the large tube on the Miata filler neck
e) Sender: So it can lie to me about how much stuff is in there
f) Fuel pump electrical: So we can pump stuff out and burn it

The one I'm having trouble with at the moment is (a) Fuel Out. The obvious solution here is a bulkhead fitting, something like:

https://www.pegasusautoracing.com/produ ... RecID=7519

In the book Kurt (rightly I think!) has concerns about what happens if they get loose. (You're screwed!). I'd rather weld a bung and have attachments either side, one to the fuel pump and the other to the AN Hose, but I have searched everywhere to work out how to do this and what parts to buy.

Help? Anyone?

:?:

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Re: Fuel tank confusion...

Post by Midlana1 » 20 Mar 2020, 18:46

Yes, AN bulkhead fitting, like what I did on fuel tank v2.0 and its removable plate assembly. Note the nuts welded to the plate.

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Re: Fuel tank confusion...

Post by steveo » 20 Mar 2020, 20:32

Oh I see. They’re a bulkhead fitting but with the inner nut replaced with one welded to the plate right? Now you say it it’s obvious but for some reason I couldn’t work it out!

Thanks!!

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Re: Fuel tank confusion...

Post by ChrisS » 21 Mar 2020, 02:29

Should you choose, you could simplify that a bit by using an in-tank FPR and return and only having a single dead-headed feed to the fuel rail. Just need a vent then.

This is the solution most OEMs use now and the one I used on mine, given I'm using an OEM Lotus tank and fuel pump/FPR setup. The donor car had an identical arrangement too, despite being a 1995 or so design.
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Re: Fuel tank confusion...

Post by bgkast » 14 Apr 2020, 13:30

Why not use the fuel pump module from the engine donor? It should have the fuel level sender included, but you will have to adjust the float to work with your tank.

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Re: Fuel tank confusion...

Post by Midlana1 » 14 Apr 2020, 14:29

Right, the height may have to be adjusted, and you'll need the matching mounting flange.

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Re: Fuel tank confusion...

Post by ChrisS » 15 Apr 2020, 00:26

Using the donor assembly had been my plan, but the assembly was too big to fit in the hole of the Lotus tank, which was a shame. I detailed it in my build, but I got a Lotus unit and modified the gauge sender to match the Alfa one as I’m using the Alfa gauges.
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Re: Fuel tank confusion...

Post by bgkast » 15 Apr 2020, 13:36

I had the same plan and issue as ChrisS. If using a Lotus tank the easy button is to use the matching fuel pump module. Hint: there are several Toyotas that use the same assembly. I used one from a mid 2000s Celica. Make sure to upgrade the pump if the Lotus/Toyota pump does not flow enough for your engine.

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