100 liter center fill tank

[mscott842]

I have undertaken the challenge of re-creating a center-fill carbon fibre gas tank for a 1968 race car. The tank and molds are complete. But now I need to design the center-fill neck and cap, and the opening in the deck lid. What diameter. Does anybody know of an original center-fill tank that can be photographed. I need to see the hole as looks from under the deck lid. I'm hoping to have some repros of this tank avaliable sometime in the future.

[Grady Clay]

I am in favor of a center-fill fuel inlet only if it is properly done atop
a fuel cell. Yes, you can take a steel or plastic Factory tank and
modify it into a container for a flexible fuel cell. You should check
the regulations for a custom fiberglass (FG) or carbon fiber (CF)
container.

The critical issue is the fill cap for the fuel cell should NOT be
the flip or screw cap at the hood.

The fuel cell, its installation, the plumbing and associated hardware
deserves serious attention. Gasoline is the most dangerous
substance you normally ever come in contact with. This is
particularly true in your race car. A burn injury is devastating

Here is a basic diagram. Some detailed explanation is necessary.

Attachment 20847

Note that the show cap and show neck are not firmly attached
to the fuel cell. They are designed to come off in an accident
and not damage the safety fuel cell.


The safety fuel cell is a flexible container with one large service
opening on the top. The cell contains anti-slosh and explosion
prevention open foam. The cell may also contain anti-slosh baffles,
a smaller pick-up container and even a submersible fuel pump.

The opening cover plate is sealed with multiple small screws to
distribute the clamping force. The opening cover plate contains
the hose connections for supply, return & vent in addition to the
fill cap. The neck of the fill cap should be as short as possible
and integral with the cover plate. The fill cap, neck and fittings
should be protected with a collar that is integral to the cover
plate. The purpose of the collar is to protect the filler and
fittings in an accident.

The safety fuel cell is inside a substantial container (usually metal)
and is lightly attached with several safety tabs between the cover
plate screws and not bolted to the container. The purpose of this
is to allow the container to deform independently of the safety
fuel cell so the cell isn’t damaged in an accident.

The container should be strapped (not bolted) to the chassis and
mounting framework. The straps should be free on the container.
Again the purpose is to allow the chassis to deform in an accident
yet not damage the container or the safety fuel cell. Usually there
are four straps – two fore & aft and two side-to-side, straddling
(but not on or too near) the cover plate. The straps should go
from the chassis up, over the container and back down to the
chassis. Steel ¾" strapping works great.

All the hose connections should be screw-on. That includes the
supply, return, vent etc. All of the hoses should be clamped to the
cover plate or collar about 8-12 hose diameters from the junction
of the hose to the fitting. This prevents stress at that connection.
Use padded “Adil” (sp?) clamps.

There should be about a foot (30 cm) of extra hose in an S-loop.
This allows the safety cell, container and chassis to deform and
still not stress the hose connections. After the S-loop the hose
should be clamped to the chassis or other near the next hose fitting
as above. The intermediate hose in the S-loop should be secured
with small zip-ties to prevent flopping about in normal use but not
so securely that it can’t function in an accident. You want the
safety cell, container and chassis mounts to all be deformed and the
hoses have enough slack to not rupture and spill fuel.

Every hose in the fuel and oil systems should be installed this way.

The fuel breather should have an integral check valve in the cover
plate. This should seal the vent when not in the normal upright
position. The vent hose should go up to a high point under one side
of the cowl and then vent down at the forward center of the car.
The purpose here is to prevent gravity draining of the fuel if the
car is on its side or roof.

The cover plate needs an electrical ground to the container and then
to the car chassis. Small braided straps are best. If you have
electrical devices at the fuel cell (level sender, fuel pump, etc.) use
separate grounds and appropriate wiring and insulation (several
layers), strain relief and S-loops as above.


Your center hood filler can be large enough to reach in and open the
cap at the cover plate. I would only loosely (no clamps) mount the
show neck to the cover plate collar. This way it can’t damage the
fuel cell in an accident. Be sure and ground the show neck and cap
assembly. A long funnel down the show neck will prevent spills. You
can make the funnel just large enough to securely fit in the filler at
the cover plate so it is large enough to accept your dip-stick level
gauge.

Remember to position the foam in the safety fuel cell so it isn’t
damaged when checking the fuel level.

A fuel cell is not like your regular gas tank. It requires regular
maintenance (in fact so do regular 911 gas tanks but that is another
subject.) At least annually the safety cell should be removed
from the container. The container cleaned and the outside of the
safety cell inspected for any damage. Sand between the container
and safety cell can do serious damage to the safety cell.

The foam should be removed and inspected. The safety cell should be
clean inside (nothing came in with the fuel and the foam isn’t
disintegrating). The cell should be stored dry with the foam removed
during the off-season. The foam should be replaced every three years
or per the manufacturer. This stuff has a definite life span. New
gaskets/seals should be installed every time.

After you have reassembled the safety cell, fill it with fuel, cap the
fittings and lightly squeeze it. Look for any signs of the tiniest fuel
leaks. There is no such thing as a leak small enough to ignore so
don’t bet your life on it.

There should not be ANY fuel connections in the cockpit. The fuel
lines should start and end outside the cockpit with only a protected
continuous pipe/hose in the cockpit. No leak at a fitting should be
able to find its way into the cockpit.


A safety cell can be installed in a modified standard fuel tank in
many instances. In some cases it takes two standard tanks to
make a suitable container. In almost every case the same above
principals apply.

In every case, fuel pick-up is an issue. The best systems have a
small safety “surge cell” inside the main cell. There are two fuel
pumps; one to keep the surge cell full and overflow back to the
main cell and one to supply the engine from the surge cell. This
can be designed where there is an “early warning” as the surge
cell is no longer being refilled.


BTW - Safety retention straps on the hood and filler neck should
be long enough for the hood and other to go above the windshield.
You don’t want your vision blocked.

Another safety consideration is the “fire wall.” On our cars we have
two, one between the engine/transmission and the cockpit and the
other between the front trunk area and the cockpit. When a 911 is
prepared for racing, usually there are a lot of extra holes and
passages. Too often these are covered with thin aluminum. If
anyone has seen an automotive fire, the aluminum will melt and drip
away almost as fast as plastic, faster in some cses. These holes
and openings should be covered with steel and preferably welded
completely sealed.



Every installation is slightly different.
Safety should be your #1 concern.

I can't bring myself to post a 911.
Attachment 20848

I have several Pelican posts on this subject.
A ”Pelican Search” will turn them up.

Best,
Grady

[tadd]

Grady:
That has to be the best post I have ever seen by you or anyone (and I have looked up all yours on pelican ).

Thanks!

tadd

[CurtEgerer]

Excellent info/ideas!! Thanks Grady.

[TRE Cup]

mscott842:

Sent you an e mail
Dave