I have been grappling with the swirl pot problem (SD1 EFI V8 into '78
MGB), and here is my current approach:
I hesitate to modify the stock tank for a number of reasons. I don't
want to lose any useable fuel capacity, and adding a swirl pot like the one
in the SD1 tank to the relatively shallow flat bottomed B tank looks like it
would do so.
The next idea is to use a separate small surge tank to feed the Bosch
injection pump. This surge tank would be fed by an electric pump on the
stock tank, which can remain completely stock. The surge tank then feeds a
pickup for the Bosch pump, and can be shaped so that the pickup will not be
uncovered even on severe cornering. While crawling around under the car, a
good location for such a tank appeared to be where the left hand battery
would have been on an early B with 2 batteries. When the switch was made to
a single battery on the later Bs, this space was left open. There is enough
room between the two stiffening brackets, and ahead of the axle, to mount a
tank of 1 or 2 gallon capacity. I envisioned using a float and needle valve
arrangement in the surge tank to control the flow of fuel into the surge
tank, then a pickup feeding the Bosch pump mounted nearby at the level of
the bottom of the surge tank to get good gravity feed, with the return line
from the pressure regulator going back into the surge tank. This way the
pump on the stock tank would pump only as much fuel as the engine was using,
and the Bosch pump would operate normally.
The advantages of this setup are that a tall narrow surge tank can keep
the pickup covered and the system will actually gain usable fuel capacity.
The disadvantage appears to be that the engine now depends on two fuel pumps
to stay in operation- use reliable pumps, and this is not a real problem.
I took some rough measurments of the space available for the tank, and
it looks like about 7.25" wide, 11" long, and 10" deep to be flush with the
floor pan of the car.
I spoke to John McCrea at Fuel Systems Engineering in Whittier,
California, about fabricating a tank. John is into ocean racing boats, a
couple of THOUSAND horsepower, running EFI, and has extensive experience
working with custom EFI setups. He suggested that rather than complicating
things with some sort of float valve to shut off fuel flow into the surge
tank, that a return line from the surge tank back to the stock tank be
plumbed in, and the electric pump on the stock tank allowed to run full
time. This simplifies the system and ensures that the surge tank would
always be filled.
John has tons of catalogs and suppliers in the race fabrication world,
and is going to look for a production tank of some sort that will fit in the
available space and be cost effective- something like a dry sump oil tank,
or a "puke tank" that can be modified easily with the required fuel line
fittings. If a suitable production item can't be located, we will look at
fabricating from scratch. I agreed to let him poke around for a couple of
weeks, as he is pretty busy.
I will post an update as needed.
Scott Pontius
'78 MGB with half plumbed and wired SD1 V8
Los Angeles
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