Do you want crank you
car’s performance level up a notch? Many experts today feel
that the only way to go is with aftermarket programmable fuel
injection, but there are also folks who feel that computers are
for the office, not for racing. That real cars have a heart, and
that heart is made of metal, not circuits. It’s the old
argument: what’s better, carburetion or fuel injection?
One common viewpoint is: “fuel injected cars start easier,
idle consistently, and you can easily control the fuel mixture to
optimize performance.” A counterpoint endorses a more
classic view of the automobile: “carbs are what gives a car
it’s personality. They’re a simpler concept reminiscent
of simpler times. You feel more connected to the car because you
get more hand’s on involvement”. You can hear
discussions similar to this one in garages all over the country,
and the participants often become passionate about their views.
But before we start duking it out, we thought it it would be a
good idea to take a long hard look at the pros and cons of both
systems.
POINT: Traditional Power by Mike Ancas
For the conversion
to dual carburetors, we knew that we had to do everything just
right in order to be competitive with aftermarket fuel injection.
Most readers are familiar with the problems that can be
encountered when dealing with hi-performance carburetion, but
this poor reputation dates back to a time when carbs were
generally unreliable and difficult to adjust properly.
There is a new generation of carbs that are much more user
friendly and can always be set up quicker and easier than
installing an aftermarket EFI system. TWM, one of the leaders in
intake technology, sent us the latest in manifolds and linkage to
take full advantage of the dual carb set-up. We turned to
Advanced Engine Management in Gardena, California for our
carburetors since they are the largest West Coast distributor of
Weber and Mikuni. Steve Trinkaus at AEM knows both carbs and
aftermarket fuel injection systems, and can assist with any
intake or ignition need. AEM can also rebuild old carbs for
around $125 each. We chose to go with Mikunis over Webers because
they are externally adjustable, and Webers are not.
The next step was to deliver a consistent fuel flow of at least 3
psi to the carbs. That meant getting rid of the stock fuel pump.
A new electric fuel pump was installed next to the fuel tank in
the rear of the vehicle, and an inexpensive Purolator fuel
pressure regulator was installed along the fuel line just before
the carbs. Once the above steps were completed, all that was
necessary was to remove the old manifold, carb and pollution
control equipment. This turned out to be the most time consuming
part of the project (took about an hour). Then the new manifold,
carbs and linkage were secured into place - done. Everything just
bolts right on. We chose to match all of the ports, both on the
head side as well as the carb side, to further optimize intake
flow. At this point in the conversion, we knew we would be way
ahead of the aftermarket EFI project as far as ease of
installation and time commitment.
COUNTERPOINT: Electronic fuel injection by Dennis Witt
Technology has a
subtle way of changing our daily lives. The amazing advances in
micro chip development has revolutionized the century old process
of mixing a fuel and air mixture in the modern automobile engine.
In a very short time span, the manner in which competitors have
attempted to maximize horsepower and torque curves has been
dramatically altered by the combination of computer power and
fuel injection.
Historically, the fuel injected cars were a rarity, primarily due
to the cost of the system and its mechanical complexity. Today
what was once impossible is now feasible at a very reasonable
cost in both time and money.
There are aftermarket systems available now which allow for the
conversion of the old and outdated carburettored vehicles to take
advantage of the powerful new electronically controlled fuel
injection systems. Our comparison should validate the theory that
a carburetor conversion “sucks” when compared to an
electronic fuel delivery system that “injects”.
The heart of our fuel injected system is comprised of an intake
manifold and throttle bodies supplied by TWM, who manufacture
components that are compatible with both carb and EFI systems.
Injectors and technical advice were provided by RC Engineering,
who has just about any size injector in stock and can tailor a
“wet” system for any vehicle.
The brains of our conversion was handled by a compact computer
developed by Racetech. We quickly discovered that the name
“Simple Digital Systems” says it all. No more having to
rely on a laptop to set individual air/fuel parameters. The SDS
computer is small, self-contained unit that can be programmed
with ease. To summarize: Hardware = TWM; Wet system = RC
Engineering; Electrical = SDS. We found, however, that with EFI
systems: you get what you pay for. The SDS system is inexpensive,
and it works, but not as well as a Motec or Electromotive.
Now a bit of advice for anyone attempting an EFI conversion:
start with a fuel injected car! Converting a car that was not
initially designed for fuel injection is a difficult process.
Carbs only need 3-4 pounds of pressure, however it takes 40 to 50
pounds to run fuel injectors. If you start with a carburetored
car, you will find that none of the existing fuel lines or hoses
are capable of handling these higher pressures. So the first
modification you face is how to get the fuel from the gas tank to
the injectors without causing your fuel lines to burst. The
solution requires the installation of a larger diameter stainless
steel fuel line from the tank to the engine compartment (a
difficult and dirty task). That having been accomplished, if you
haven’t taken a sledge hammer to the car in frustration yet
and still want to move on, you will now need a get high pressure
fuel pump to keep the hungry injectors happy. We chose a pump
manufactured by N.O.S and distributed by RC Engineering. This
pump puts out over 100 lbs. of pressure at the outlet. Next, AN
fittings need to be attached to the fuel pump and plumbed into a
new stainless steel line. Not using the highest quality
components could result in a rupture of raw gas spraying over
both electrical and hot engine parts, resulting in a fuel fed
fire rendering all of your hard work into a glob of melted metal
and rubber.
We chose a 3/8” diameter steel line to handle the additional
fuel flow, connected to a high pressure fuel filter to insure
that no contaminants clog the expensive system. The stainless
steel line conversion was one of the most difficult parts of the
project.
Another frustration we faced was that the individual parts used
to install an aftermarket EFI system come from different
manufactures, hence the project is not an “insert part A in
tab B” process. A significant amount of time was expended
trying to figure out how the entire system would be tied
together. If your header is not fitted to contain an oxygen
sensor, then a hole must be drilled so that a 22 mm nut can be
welded in position. Your EFI system won’t know what to do
unless it get feedback from an oxygen sensor.
Additional problems encountered were that the Lucas injectors we
wanted to use were not compatible with the SDS system, and there
was a grounding problem that occurred when a wire inside the
throttle position sensor was broken. When you choose which EFI
system to use, make sure that you provide all necessary
information to the injector supplier.
The moral of the story is that there are many things that can and
will go wrong when you tackle a conversion like this. If you
mentally prepare yourself to face these problems before you
start, it could help preserve you sanity.
Time Commitment
The carburetion
conversion is much more simple to undertake, period. With all
components on hand, it can be done in one day. In summary, if you
are starting with a carburetted car, you should add a more
powerful fuel pump that can deliver 2-4 psi of fuel pressure.
A trip to the local auto parts store can give you several to
choose from for under $75. Switching fuel pumps can often be a
dirty job, and some improvising may be necessary, but an average
mechanic will have no trouble with any part of this carb
conversion project.
Removal of the stock intake system and replacement with a TWM
intake is a no-brainer. You will need to add some fuel hose in
the engine compartment, and splice in an adjustable (1-5 psi)
fuel pressure regulator (a fuel pressure gauge is also
recommended). Then, some fiddling with the throttle and choke
cables should complete your labor of love.
The EFI conversion, on the other hand, will take a tad longer. We
recommend starting with a fuel injected car in the first place.
That will save hours of labor converting a fuel delivery system
that is used to providing fuel at 1-2 psi, to one that can handle
60 psi. If you don’t change the fuel hoses, the new 60 psi
fuel pump will cause the weaker hoses to explode fuel into every
nook and cranny of your nice little car.
If you have never replaced all of the fuel hose in your car, you
haven’t lived. There is a great sense of satisfaction that
comes with completing the task, similar to the feeling you get
when you have been beating your head against a wall, and then
suddenly stop.
Installing the new intake manifold is no big deal, but there is
more fiddling required than with the carb conversion. Some intake
manifolds designed for aftermarket EFI systems utilize a throttle
cable system that operates from below the intake manifold. If you
stock system is not like that, add a few more hours of work to
your project.
Another problem we have seen with some EFI intake manifolds is
they require more spring strength to keep the butterflies closed,
and many stock throttle cables can’t withstand this tension.
A day at the track can be ruined when your throttle cable gives
way under the pressure (don’t ask us how we know).
Fine tuning
Carburetion
systems have been given a bad rap when it comes to fine tuning.
Playing around with jetting can drive you a little crazy. But it
is, at worst, a trial and error ordeal, something that any moron
(even us) can endure. The shop that sells you the carbs should be
able to give you a good starting point, and you can take it from
there. Plan to spend anywhere from a few weeks to a few months to
get the set-up that best fits your application.
On the other hand, the EFI systems are not easy to set up either.
The problem is there are so many parameters, you don’t know
where to start. Even when you get some initial guidelines, the
amount of variables you need to manipulate can be mind-boggling.
It takes a great deal of experience (again, mostly through trial
and error) to get the hang of it. And in the end, you will find
that you are speaking a different language than your friends.
When you tell them your car is running a little rich today
because your water temperature and manifold pressure seem to
effecting the duty cycle of your injectors (which is dependent on
the MAP sensor and degree of dialed-in knock/retard), they will
look at you as if you are retarded. If that happens, just scratch
your head, declaring that you figured out that your closed loop
high parameter needs to be 14.1 inches in order to obtain
stociometric balance. That will shut them up.
The bottom line: Horsepower and Torque
Dual carburetion,
if done correctly, can net 20-30% more horsepower and a little
more torque. Some dual carbed imports are putting out over 200
hp, however dyno tests show that much of that power isn’t
achieved until after the tach goes above 7K. On the other hand, a
fully sorted-out aftermarket EFI conversion will usually add
about 5-10% to that number. So when it comes to raw power, the
SDS system will almost always beat a dual Mikuni conversion. And
with an aftermarket EFI systems, your torque curve can be
customized to deliver power wherever you need it. So when it
comes to torque, the EFI systems really stand out.
So the bottom line is that the EFI systems can deliver slightly
more horsepower, and even a stock EFI system inherently will
provide better low end torque. Add to that the adjustability of a
system like the SDS unit, and the torque can be placed right
where you need it most.
But you need to consider what type of racing you want to do with
your car before deciding which system to buy. The Solo II street
prepared class is infested with aftermarket EFI cars, but to run
an aftermarket EFI system in a prepared classes will cost a 150+
lb. weight penalty, and most drivers feel that this is too much
weight to spot the carburetored cars. That’s why dual carbs
remains the hot set-up for the prepared classes.
Tunability
Due to the
multitude of parameters to consider, which in turn gives way to
an infinite number of programming combinations, initially setting
up an aftermarket EFI system is a long, tedious undertaking. On
the other hand, dual carbs (although no walk in the park) are
much simpler to set up. But that’s where the advantage ends.
Once you get the knack of an EFI system, you can get it to do
just about anything you want.
So you get to the track, and it is a hot humid day. No problem,
once you have a program stored for this scenario, you will be
crossing the finish line ahead of the carbed cars.
If you have ever seen the Pike’s Peak Hillclimb, you may
have heard that most of the fastest vehicles have EFI computer
systems on board that can adjust the air/fuel mixture dozens of
times per second! They get to the top first because the
atmospheric conditions at the starting line are vastly different
than at the top. With an altitude change of over 7,000 feet , you
could start out with a hot, sunny day and end up in the sleet and
snow. And don’t forget what 15,000 feet does to the air
pressure. If you have a hard time breathing at that altitude, it
is a sure bet that your car does too. The computer in these
aftermarket EFI systems can adjust for this variable, and
carburetors can’t .
Reliability
With todays modern
carburetors, reliability is not as much a problem as in the past.
We had a pair of Mikunis that ran great for years, but eventually
the throttle bodies began to wear and very small vacuum leaks
appeared around the shafts. This is the same kind of problem that
many British cars develop.
But throttle bodies on the EFI engines can also wear, and often
they are under more stress. This is because an EFI system can be
more sensitive to the loss of vacuum that will occur if your
throttle doesn’t completely close. For this reason, larger
throttle return springs are often used, which tends to put more
tension on the entire linkage assembly, thus increasing wear to
the components.
And injectors don’t last forever, either. They can clog,
wear, and once the spray pattern and flow rate has been altered,
you must have them cleaned. Professional cleaning will cost over
$100 per set, and sometimes cleaning won’t help. Replacing
an injector adds additional expensive. Remember to replace your
fuel filter (also more expensive on an EFI car) every year or
two. Your injectors will be grateful.
Then there’s the higher pressure fuel pump, which works
harder and is more expensive than the low psi unit on the carbed
cars. If one of those wears out, the EFI pump will put a bigger
dent in your wallet. Of course, these are about the only parts of
an EFI system that wear.
So when it comes to reliability, maybe we should call it a draw.
But if something goes wrong, it will typically cost more money to
replace components in an EFI system.
CONCLUSIONS
Actually, the
choice as to whether to go with dual carburetors or an
aftermarket EFI system is a simple one. You should base it on
what you are planning to do with your car, and how high the
credit limit is on your Mastercard. If you have some bucks, need
low end torque, tunability and have plenty of time on your hands,
then the choice is simple. Get yourself injected.
If, however, you are in more of a hurry and only want to spend
hundreds instead of thousands of dollars, then dual carbs may be
your best choice. Either way, you will have a killer car when you
are finished with either conversion and experience full blown
performance.
- Specific applications for your Import car are discussed in each of the Performance Handbooks listed on the main page -
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