.Fuel Systems For Our Cars
By
Karl Schluter
This article will cover tips on fuel pumps, fuel line
lay out and fuel tanks on carbureted cars.
More on the relevant pumps and fuel rates is covered
on the companies web sites on the internet, what I hope to do here is highlight
a few of the main points I see that get overlooked on installs of bigger fuel
systems. Do Google the fuel pump company’s web sites as some have very good
guides on flow rates etc relevant to HP ratings. Both
Barry Grant and Holley have good info, as does the Century site for Mallory
pumps and regulators.
The stock fuel system on our cars is pretty good.
Indeed I have had the stock mechanical pump on the factory in-line 6 engine
feed 3 down draught Zenith Mklll Zephyr carbs to over 7000 rpm. It can also
feed 3 SU side draught carbs. However for the latter I would install a fuel
regulator that would lower the fuel pressure to 3-4psi, while this is the
stated pressure of the stock pump, it can spike upwards. Avoid the common
chrome dial type regulator, these often fail and have been the source of many
engine bay fires. A much better regulator is the base model Holley regulator or
the Filter king model (further on I will explain the use of regulators). Avoid
imported copies of fuel system parts if you value your car, money is better
spent on better made, safer parts.
If the demands of your engine exceed the stock
mechanical fuel pump then the next choice is either an up-rated mechanical pump
if the engine is one that has higher volume pumps available for it, or an
electric fuel pump. One advantage to the mechanical pump is when the engine
stops so does the pumping of the fuel however they can heat fuel too. This
helps cause fuel vapour locks.
To run an electric pump on a high HP engine you first
need to look at the fuel lines. The stock fuel line inside a
Zephyr/Zodiac/Consul fuel tank is a tube about 5 mm or 5/16” in size, flattened
and soldered to the bottom of the tank with a cut in the side of it for fuel,
yes really!
This will not
supply an engine much over 150bhp. In the past I have taken my fuel tanks to a
radiator shop and got them to weld a larger fuel pick up pipe in the tank, a
3/8” size line for up to 400hp and ˝” for more. The reason I get a radiator
shop to weld the line in is that even a well flushed fuel tank will have highly
flammable fuel vapour in the seams, radiator shops are more experienced at the
different methods used to weld on a used fuel tank. If you are not able to get
a professional to weld on the tank, you could screw a brass elbow into the sump
plug area of the fuel tank. I used an elbow that took a hard tube fuel line
3/8” size. You can buy an “olive” that goes over the tube for a leak free
fitting.
DO NOT TRY TO SOLDER OR WELD ON ANY USED FUEL TANK
YOURSELF!!!
Keep any portable electric lights away from a possible
splash of fuel if working on the fuel tank.
A poor fellow lost his complete car when his trouble
light fell into a container of fuel under a car on work stands, this can happen
to anyone if you are not being careful.
I do recommend if you do end up with a ˝”pick up pipe
in the tank that you get the fuel tanks vent pipe size increased as otherwise
this can restrict fuel leaving the tank. (Often you will see plastic fuel cell
tanks that have the topside sucked in/down; this is often because of too small
of a vent). The vent should feature a one way valve and have at least one
360-degree loop.
Before any fuel pump you want the first fuel filter.
Few do this and wonder why their fuel pump stops working. The stock fitted tank
has no filter sock inside on the pick up fuel line so you MUST run a filter
before the pump. Sliding vane pumps like Holley blue and red pumps are bad for
jamming if dirt etc gets into them. The Holley pumps get a bad rap when often
it’s the clown who incorrectly installed them at
fault, ie: the tank is full of junk or there is no filter, no relay or even a
fuse on the pump. All of these points need considered when installing an
electric fuel pump.
The choice of electric fuel pump can depend on the
size you need, pick a pump that is build for running long periods of time (some
bigger pumps are short term use only).
Look for the gallons per hour (GPH) rating of the fuel pump and whether
you need a regulator with it. I could cover it here but it varies with pump to
pump and end use of your car so use the company’s web site you would like to
choose the best-suited pump from. Use their tech lines to e-mail them with your
set up to get the best advice.
I have had good results with the Facet brand of fuel
pump. Both the cube model and the cylinder model are used widely from factory
cars to micro lights. They have bigger models that can do some V8’s as well.
The Ford GT40 was one car often fitted with the Facet Cylinder pumps, as were
many European performance cars. For Weber carbs I recommend the Carter line of
fuel pumps, remember to keep with in the 3-4psi range for Webers and SU’s.
Holleys prefer 6-9psi max. This is needed at the max speed and rpm of the
engine in your car. If you can, mount a pressure gauge onto the line going to
the carb and read it from inside the car under full load while driving at a
quarter mile track or club day run etc. Do not do this on a public road. Plus
the pressure gauge must stay above 7psi and not be feed via a fuel filled line
into the interior of a car ever! That’s a huge fire hazard. Some companies sell
an isolator that extends one half of the fuel gauge line with a non-flammable
fluid so the line can go into the cars interior. An electric fuel pressure
gauge is great too if rated for fuel use as a way to mount a fuel psi gauge in
the car without a pressured, flammable line.
There are pressure gauges sold to mount at the fuel
line right at the carb and to be read while setting the regulator, use a good
one (again you don’t want it to spring a leak one day over your hot engine).
Some have had trouble with creeping pressure (raising
pressure) once the engine heats up, this is mostly because a damped pressure
gauge is being used and the liquid inside is expanding therefore giving an
incorrect reading. Be aware of this or use only an undamped pressure gauge.
The Holley Red
and Blue pumps are good and parts to rebuild them are cheap. Mallory make a
very sound fuel pump line too, as does Carter. Avoid the imported copies of the
Holley pumps.
Some feedback
from people who have run the above mentioned pumps are not always good; however
as mentioned, many incorrectly install them or use the wrong model.
Do consider if the replacement fuel pump needs a fuel
regulator as well. I strongly recommend running a fuel system with a by pass
regulator over a dead head system if a regulator is needed. What? A Dead head
regulator restricts fuel pressure down to what the carb likes and holds the
fuel in the fuel line back to the tank at a set pressure. The bad side of this
is the fuel flow stalls to a halt in the fuel line depending on demand and can
heat up in a hot engine bay resulting in a vapour lock. It can also make the
fuel pump work harder (but not in every case as some fuel pumps have relief
valves built in), but regardless the fuel will heat up forward of the pump in
the fuel line.
The by pass type of fuel regulator returns fuel not
needed rearward via a return fuel line (the same size as the forward line or
one size bigger) back to the fuel tank. This results in a cool supply of fuel
to the carb and again less stress on the pump. Note: the end of the return line
should be pumped into the fuel tank/cell away from the fuel pick up, (otherwise
hot and aerated fuel will return to the pump). Have the return line going down
to near the bottom of the tank so that it’s under the fuel level most of the
time, this stops aerating of the fuel.
A regulator is only needed if the pumps rated
psi/pressure is higher than what the carburettor(s) needle and seat can handle.
Unless running a very high volume fuel pump with excess pressure I would just
run a dead head regulator, this means one without a fuel return. Some lower
pressure pumps do not need a regulator of any type as the pump itself has a
bypass.
While pumping excess fuel back to the tank via a fuel
return regulator seems a waste, it however uses the fuel tank as a radiator
allowing cooler fuel to be pumped forward to the engine further decreasing the
risk of vapour lock. Most electric pumps if mounted correctly will eliminate
vapour locks by better keeping the fuel under pressure so it can not go into a
vapour. A car operating in a hot environment or parked up with high under bonnet
temperatures is more prone to vapour locks; use of an
insulator under the carburettors body, shielding on fuel lines and increasing
air flow through the engine bay will all help too.
As mentioned bad
feedback on the above pumps can often be traced to poor installation. For instance, the cube facet pump is supposed to be
mounted in-line with the bottom of the fuel tank (the best place for all
electric pumps) and close to the tank so it pushes fuel, rather than sucks
fuel. This helps the pump self prime and will reduce wear in the pump. Yet I have often seen these pumps fitted up
on the hump over the diff or in the engine bay, no wonder the poor pump has
trouble. There is also a valve inside the cube pumps that require the cube
facet pump be mounted at a 45-degree angle. One mistake I see even in high
dollar cars including race cars is an electric fuel pump mounted with the
electric motor body pointing downwards, or the pump lying on its side, an
accident waiting to happen. If the seal in the pump leaks (and they often do
weep over time, most pumps have a relief hole for this very reason) the fuel
will drain straight into a hot electric motor……...
If you want to run two pumps, say one as a back up,
this can be easy if you are using a fuel cell type tank, as a lot have twin
outlets. However after the two pumps you will need two check valves to stop
fuel pumping backwards through the other pump. Some pumps have check
valves-certain Facet pumps do, these are not to be confused with a bypass valve
as fitted to Holley pumps etc.
Some pumps come with rubber mounts in the installation
kit to quiet them; small engine mounts from motorcycle shops can be used too.
Some exhaust pipe mounts work well, they are rubber round blocks with a
threaded stud on either side making it perfect to rubber mount an electric
pump. You will need to run an earth wire from the pump body to the chassis.
Don’t mount a pump to a flat section of sheet metal; this will amplify the
sound of the pump!
Again the main points are to mount the pump close to
the bottom of the tank, upright and with a filter before it. This also raises
the point of running fuel pumps inside your boot/rear trunk or not. I think its
up to the owner, both have pros and cons. I do suggest you allow provision for
fuel to drain from the boot if the cell or pump and lines start to leak. Also
wire in a relay and fuse.
The fuel filter
does not have to be a very fine one, some use a finer filter after the pump, and
I found Weber carbs gave trouble if not fitted with a fine filter in the line
before the carb. More so than say Holley’s. I run a
fuel injected tin bodied fuel filter, they are fine filters that are strong and
are going to easily stand a carbureted fuel pumps pressure.
When running a fuel line up to the engine bay, use
proper steel or alloy tube over braided line or rubber fuel rated line. I don’t
like a long length of braided line under a car, really it’s often not much
better than rubber line except for a woven mesh covering, and it won’t last as
long as tubing or take the same beating. If using braided line in the install,
use noted brands, beware of off shore no name line, as it won’t have the same
liner inside that better hose has.
The rubber lining will break down over time, do it
right with tubing in the first place like the factory. I have found shops that
sell alloy sheet sell the tubing as do better car part shops. A newer rubber
type line is the blue coloured line that pushes onto barbed fittings, I have
used this on oil pressure lines and the fittings are 100% sealed. They do not
require a hose clamp.
A generator or
alternator pulley is a handy hand held object to bend tube around to make a
nice flowing bend. Some shops sell affordable tube benders as well. Avoid brass
fittings that have a sharp 90-degree angle, as they will restrict overall flow.
Keep the fuel
line away from heated items like exhaust pipes and mufflers and clamp it every
500mm with Adel like clamps. These are alloy clamps with a rubber liner, you
can fabricate your own using alloy scrap sheet metal and left over fuel hose.
A tip: To keep the fuel line away from hot exhausts in
a car, I run the front half of the fuel line outside the front chassis rail but
inside of the sill area. From near the end of the gearbox, under the car, I
move the fuel line out closer to the sill around the box formed chassis rail. I
then drill the front jacking point cross member and with rubber grommets run
the fuel line through the jacking point and up the underneath of the driver’s
side RH mud guard.
Two advantages
from this method are:
1, the fuel
line is away from heat,
2, the line is
protected if you blow the clutch/flywheel or bell housing.
I then run the fuel line through a grommet into the
engine bay at the area of your choice. When buying fuel hose, make sure it is
correctly rated to carry fuel. It will have it in white lettering, use a known
brand like Dunlop etc.
Do fuse the fuel pump and wire in a relay as well, but
remember to use the right gauge of wire please, same for any earths too. This
will ensure the pump sees full voltage. Also you can wire in a hidden switch to
have the car run out of petrol if someone takes your car for a joy ride.
I strongly
recommend you wire in a collision switch, these are factory fitted on new cars
and should have been made law in the cert laws in NZ at least for modified cars
running an electric pump. The switch turns the fuel pump off
if you are disabled in a crash, making the chances of you surviving better plus
making it safer for people attending a collision etc. The switch we have
listed in the FAQ and Part suppliers section comes with full wiring
instructions and is under $NZ50 so there is no excuse not to run one, The pump
switch is reset with a button. Once you have your fuel system plumbed out,
switch it on to pump fuel through into a container to flush the line of any
junk from fabricating lines etc.
Some added advantages to electric fuel pumps are you
can quickly fill an empty float bowl instead of cranking the engine forever to
manually fill the float bowl(s). Setting float levels is easier too as it can
be done without the engine running on carbs with sight holes. One thing often
over looked when setting floats is that excess fuel must be first used/drained out if you lower/readjust the float setting.
Otherwise until that fuel is used you will not get a true reading of a reset
float level.
Here are some tips on installing a Racing fuel cell
type of fuel tank. These come in alloy or poly link plastic, or the latter
fitted into a sheet metal box. There is also a more expensive FIA motorsport
rated one, which is a rubber membrane of sorts in a sheet metal box. These are
good if you want more room under the car for the exhaust or for safer track
use. Some laws may restrict their use on everyday used cars but a lot of road
cars do use them.
If installing one, use thick straps and make sure the
base is secure. Think of the total weight of 8-16gallons of fuel coming to a
sudden stop in a collision; now think of that mass being held by four small
thin tabs or two thin straps! I often see fuel cells with poor mountings. If
using a poly link cell type tank, make sure there are no sharp edges anywhere
in/on the mounts. Add rubber sheeting under the two mounting straps if using
that method.
I prefer to
have a poly link cell tank inserted in a sheet metal tank (18-22guage), go for
at least 8 gallons. Some factory made fuel cells that come in a sheet metal box
have a flange around the top, this flange is NOT
designed to hold the weight of the fuel cell. Mount the tank inside a steel
tube framed box instead.
If buying
second hand you will probably have to replace the foam inside as it can break
down and will then clog filters etc (another sound reason to have a filter
before a fuel pump), get the correct foam from a fuel cell supplier. If you
cell does not have the foam, it needs it. Shops that sell the fuel cells have
the foam in brick form to go into the tank.
The foam should fill at least 80% of the tank to effectively do its job.
This only takes up 3% of total fuel capacity. The foam does two jobs, one it
acts as baffling to stop lower fuel levels draining fuel away from the fuel
pick up and two, it stops the sudden explosion of the fuel in a fire or a
crash. (Having had my Mklll rear ended, which just about tore the stock filler
neck off the factory fuel tank, I have now decided to install one myself).
Some other tips on running a fuel cell is if you want
to run a fuel gauge you will need a sender unit that is a tube type to fit
through the foam. It will have to be the same ohm range as the stock sender
too. The Internet has how to check this out or e-mail me at: avocalea@xtra.co.nz
If you run a
poly cell fuel tank you must run an earth wire off the fuel filler ring to an
earth on the car body, this is to stop sparks caused from static when
refuelling.
Also required
is a spill bowl if the fuel cell is filled from inside the boot/trunk. This can
be an alloy or stainless bowl about 100mm tall that encloses the outside of the
fuel filler cap ie: you cut the bottom centre out of the bowl and use the bolts
holding the filler cap surround to the cell to seal the bowls bottom to the
cell. Then run a tube from the bowls side (near its bottom) to the rear outside
of the car. The idea is that if you spill any fuel the bowl will catch it. If
the fuel cell has an outside fuel cap, do use a flexible length of hose (of at
least 6” or more) to allow for the filler opening to move without tearing the
fitting off the cell on the inside of the boot/trunk. This is another step
often missed in build-ups. Lastly a good safety feature that is a rule in some
motor sport classes is an alloy or sheet metal firewall behind the rear seat,
extending to under the parcel tray area. This is to completely close off the
boot/trunk area from the interior of the car, (use sealant to seal the edges of
the sheet metal too). Now the fuel cell and battery (if mounted here) are
safely isolated from the rest of the car.
Disclaimer: The advice
and guidelines given in these articles are given in good faith. The owners
and managers of the Galeforce Zephyr site will
take no responsibility for any injuries or loss sustained while carrying
out the described tasks and procedures or any consequences arising.
Please read the Safety First Article
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