Alloy fuel tank project

[Nigel]

Hello all,
I have now received a Coupe VX fuel tank, thanks to Mark at BetaBoyz.

A few questions come to mind in order to achieve the best compromises between the various types
and requirements.
 
There are 2 breather pipes, one is 8mm, the other 13mm. They both meet inside at the same place
on the top surface and are simply open-ended. Is one enough, and if so, which size?

There are two swirl pots visible, one inside the other. Is one enough? Perhaps the larger one is there to act as a
baffle? There are no visible baffles elsewhere. I propose to have a couple of baffles fitted.

The return pipe from the engine [8mm] feeds into the smaller of the two visible swirl pots.
Does it need to go into the swirl pot?

The fuel pickup is 13mm and draws from the centre of the small swirl pop, via an unserviceable mesh filter.
I propose to eliminate the mesh, and assume external filters will suffice.

The filler inlet [46mm] on the Coupe is a long swan-neck with a stiffening brace. I propose to delete the long neck
and provide a short, say 50mm, stub to which any hose arrangement can be fitted.

The fuel gauge sender unit mounting is set below the top surface by about 30mm. Should this be maintained?

There will be more questions, but this will do for now!
Couple of photos attached for reference.
Your input will be valued. Please add anything i've missed!

Regards, Nigel

[peteracs]

Hi Nigel

As to the fuel gauge recess, you need to keep that as it needs to clear the boot floor and provide routing for the supply pipe work to the front of the car.


I also see no reason to have two vent pipes.

Personally I would prefer to keep the longer filler neck as it then comes into the boot rather than have a rubber piece exposed to the underside.

Peter

[Nigel]

Hi Peter,
I've realised there is also the consideration of the 'level of fuel' given by the sender.
If it changes, so does the reading!

I was thinking that having a filler pipe bent exactly could be prone to tolerance errors
in aiming for the floor hole.
A short hose and a couple of clamps removes this possibility.

Eric, your advice in the topic "Filthy fuel tank saga" is really useful and noted. Do you have
anything to add right now?

Cheers, Nigel

[WestonE]

Hi Nigel

In line
There are 2 breather pipes, one is 8mm, the other 13mm. They both meet inside at the same place
on the top surface and are simply open-ended. Is one enough, and if so, which size?
EW One 13mm is enough BUT actually I think the 13mm  might be the overfill return from the filler neck? and the 8mm the breather so keep both unless you are sure. On mine I have an 8mm breather via a vent valve but no car here to check right now.

There are two swirl pots visible, one inside the other. Is one enough? Perhaps the larger one is there to act as a
baffle? There are no visible baffles elsewhere. I propose to have a couple of baffles fitted.
EW One good swirl pot is enough, but listen to the experienced person making the tank. NB if in doubt go slightly larger on the swirl pot. It is effectively the tank reserve on carb cars

The return pipe from the engine [8mm] feeds into the smaller of the two visible swirl pots.
Does it need to go into the swirl pot?
EW Return to the swirl pot is wise after all this is where you always want fuel. My Aeromotive in tank FI set up does this.

The fuel pickup is 13mm and draws from the centre of the small swirl pop, via an unserviceable mesh filter.
I propose to eliminate the mesh, and assume external filters will suffice.
EW A coarse mesh to prevent stones/nuts/bolts heading down the pipe I would keep. I also view it as madness not to have a large capacity external filter pre pump especially on the IE and VX which use fine tolerance rotating vein pumps. My in tank pump has a filter sock as standard fitment and I run a second pre the injectors to protect them from pump swarf. 

The filler inlet [46mm] on the Coupe is a long swan-neck with a stiffening brace. I propose to delete the long neck
and provide a short, say 50mm, stub to which any hose arrangement can be fitted.
EW For this a straight joiner pipe to different metal pipes to suit the different shells that go up through the floor should do the job. That way the OE Neck joiner can be used. NB the straight joiner rubber joint MUST be petrol proof pipe. CBS can supply this
 
The fuel gauge sender unit mounting is set below the top surface by about 30mm. Should this be maintained?
EW Yes this should be maintained or the level sensor will not read correctly. NB In reality the tank base below has a well so tank care if the new tank is flat bottomed to adjust the height. 

I hope that helps

Eric

[Nigel]

Hi Eric,

Face-palm moment in Kent! Of course, the 13mm IS the overfill drain from the neck.

I will see what he recommends regarding a course mesh device.

My thanks to you and Peter, helped greatly.

Popping up to SMD early next week......I met and chatted to Ian already and he clearly knows
about this sort of thing.

Nigel

[Nigel]

I delivered the tank and chatted to the fabricator on Monday.

Discussed all the aspects and limitations.

A second visit today, after thoroughly crawling under my car, to tell
of spare space of around 30mm to the rear of the tank, and also that space
at the front was very tight, so a possible shifting of dimensions to ease access to
the outlets. I'm aiming to at least equal, or even gain some capacity, we'll see.

Very confident in his take on what's required. I haven't met Iain again yet, no matter,
awaiting a costing and the go-ahead to start.

Info required: could a Coupe owner please look under their car and tell me the available
space between the rear of the tank flange and the cross-beam on the chassis. Thanks.

Nigel

[Nigel]

Hi all,
The info requested above is still needed, if one of you
could take a quick look.

Thanks
Nigel

[peteracs]

Hi Nigel

Will a Spider suffice?

Peter

[Nigel]

Yes please Peter.

Assuming Zagato didn't hack the boot floor
of the shells they received! In any case,
it's useful info.

[WestonE]

Yes Zagato did extensively modify and strengthen the boot floor so you still want that Coupe size check.

[peteracs]

Thanks Eric,

Nigel, I will get measurements and photos so you can see how it locates.

Peter

[Nigel]

Thanks Gents.

I now recall that rather nice exhaust scoop in
the rear Spider panel.

Just awaiting the Coupe owner.....

Cheers, n.

[betabuoy]

Hi Nigel
Great work that you're running with this. Sorry I'd not helped earlier.  Looks like around 45mm to me.  Tricky to be very accurate because the seam sits higher than the cross-member.
Regards,
Chris

[Nigel]

Chris,
Those pipes visible.....is this the rear of the tank?

To clarify, the space between the rear of the tank
and the bodywork cross member.
N.

[betabuoy]

No, this is the gap between the tank (front) and the rear crossmember.
I guess I'm going back to garage to get under the car again!
Back shortly.

[betabuoy]

Good job you checked!  Gap now looks like 6mm!

[Nigel]

Thanks Chris, much appreciated!

[peteracs]

Hi Nigel

Sorry no photo, let me know if you need it as only chance at present is a quick look. Gap is approx 8mm all along the rear of the tank. I do not have work clothes on so diving under car not an option until Sunday!

Peter

[Nigel]

Thanks Peter, again appreciated.

The small difference between Chris's Coupe and your Spider I can
safely ignore as the mounting holes have a greater tolerance for fit.

Cheers, I'll pop into the fabricators on Monday again.

Nigel

[Nigel]

I'm happy to report that the build has started.

I had to visit the guys today to clarify the position of the filler pipe which is
different by roughly 80mm between my car [84 HPE] and the sample coupe [VX] tank.

To keep costs down and improve access to fittings, we've brought the front face back
by around 70mm. This avoids the awkward cut out that normally clears the centre
arm bolts. Capacity compensation should be provided by the square sides, and that
the rear face is approximately 12mm further back.

He did not recommend any mesh within the tank, as it would be inaccessible and unserviceable.

Aluminium tubing is only available in imperial sizes so there will be some slight but manageable differences
with the pipe sizes.