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Written By:
Jamie Harvey
So its time to start preparing the sleeper for its destiny with the turbo gods.
What we need to focus on first is the most crucial piece of the puzzle, the fuel
supply. Its really easy to just slap a turbo onto your engine and to shove tons of
air down the throat of your 420A. Having the additional air is only half of the
equation and too many people focus on the turbo setup without taking the
same time and consideration when designing the fuel system to keep up with
the demands presented by the turbo system.
After lots of online reading, research and forum jumping, I noticed that there are
roughly five different stages that most 420A owners tend to use when
upgrading their fuel system:
Next I will explain how Stage 1 works and try to point out the advantages and
disadvantages to this design.
The F.M.U.
The simplest way to add the additional fuel required is with a FMU . A FMU is
basically a second FPR(fuel pressure regulator) that is installed between the
stock FPR and the return fuel line heading back to the tank. As boost pressure
increases, the fuel pressure will increase above the set limit of the factory FPR
at an increment determined by the size of the FMU you are using. FMU's
generally are available in sizes ranging from 12:1, 10:1, 8:1, 7:1, 4:1, and 3:1.
The most commonly suggested size FMU to use on our car when using the
stock FPR and fuel injectors would be the 12:1 ratio unit (this isn't necessarily
the best choice, read on). What this means is that for every 1 lb. of boost
pressure, the fuel pressure will rise by 12psi above the static fuel pressure set
by the stock regulator.
With the stock FPR factory set to roughly 55psi static pressure (0psi of boost
present) and our system running at a maximum of 8psi of boost, that would top
out our fuel system at:
55psi + (12 x 8lbs. of boost) = 151psi!! Yikes!
In reality, it generally doesn't reach this high of a level due to pressure losses
from the stock fuel injectors having to be opened for such long durations and
the fuel pressure limits of the fuel pump. Most people have seen good results
with a maximum fuel pressure of around 105-110psi while running 8-9lbs. of
boost on an otherwise stock setup. With that being said, why don't people use
a 7:1 FMU instead?
55psi + (7 x 8lbs. of boost) = 111psi
This seems perfect so why does everyone suggest the 12:1 FMU? There are a
few reasons why. The biggest reason is simply for extra insurance. Most FMU
manufacturers will suggest this size because they honestly have no idea how
efficiently your engine responds to forced induction and there are too many
variables to consider with each customers turbo setup. All in all, this would be
a safe choice to suggest to the general public. Its better to have too much fuel
when running a turbo than it is to run too little. The problem with the 12:1 FMU
is that it isn't really regulating the fuel pressure if you are running more than
5lbs. of boost, its simply closing off the return line to the fuel tank. With just
about any aftermarket high pressure fuel pump, 100-110psi is the maximum
fuel pressure it can deliver while still delivering any significant volume of fuel.
Exceed this level and you are simply plugging the return line and reducing the
volume of fuel being delivered, not to mention you are stressing the HECK out
of your fuel pump!
The "Proper" Size F.M.U.
Okay, this is going to be a bit lengthy because I am about to explain this more
thoroughly than I have seen anyone else do, I apologize in advance. After
talking for countless hours with FMU manufacturers and Turbo kit
manufacturers for the non-turbo Ecipses/Talons, I have finally got down to the
truth about what size FMU is correct for our application.
The great thing about our car is there has been quite a bit of research and
development by major turbo kit companies, like Hahn Racecraft and Star
Performance. Thanks to them, we have a general idea of how efficiently our
engines respond to a turbo setup. Not only that, but we also have a target
range to start with for our maximum fuel pressures. Granted, the size and
efficiency of the turbo comes into play when fuel pressures are involved but
most people decide to use a turbo that produces roughly the same CFM range
as the turbos supplied in the Hahn and Star turbo kits. If you are going with a
much larger turbo than they offer....I sure hope you aren't using this type of fuel
system!
Back to the FMU situation. Like I mentioned earlier, at 8-9lbs. of boost on an
otherwise stock engine you would want to achieve a maximum fuel pressure of
roughly 105-110psi. This should provide a slightly rich fuel mixture, which is
good to prevent detonation (also the number one killer of most turbo engines).
When choosing an FMU you always want to aim a bit higher than your target
fuel pressure. If running 8lbs. of boost you would try to achieve 110psi so lets
figure out what size FMU we would need:
110psi - 55psi(maximum static fuel pressure of the stock FPR) = 55psi
So we need the fuel pressure to increase 55psi from 0lbs. of boost(static Fuel
Pressure) to our maximum boost pressure of 8psi.
Now divide the difference by the maximum boost pressure.
55psi / 8lbs. of boost = 6.875
So you need to increase the fuel pressure by 6.875psi for every 1lb. of boost
pressure. This is pretty darn close to a 7:1 ratio. Since each vehicle is different,
there are always slight variances in the maximum fuel pressures seen. With
that in mind, I would suggest the use of an 8:1 FMU when running 8-9lbs. of
boost. This would give you a maximum fuel pressure of roughly:
55psi + (8 x 8lbs. of boost) = 119psi
Vortech Engineering offers an air bleed valve HERE which you install inline with
the vacuum source to the FMU which allows you reduce your maximum fuel
pressure down a full 2:1 ratio. This will give you the ability to adjust your FMU
range anywhere from 8:1 down to 6:1 so you can dial in your maximum fuel
pressure for the best possible air/fuel ratio.
For people who think that this is too low of a ratio, just look at all of the users
who run the Vortech S-FMU unit. The maximum ratio it is capable of is 7:1 and
there are countless success stories of people who have used this setup for
many, many years with the stock injectors. People have recommended the
12:1 FMU because that is what some tech support guy told their friend, who told
their friend, who told their friend to use. Do you want the universal answer or
the one that pertains to your car? Hmm?
For anyone choosing to run only 5-6lbs. of boost, thanks to Hahn Racecraft we
know that a maximum fuel pressure of 85-90psi is generally needed. Using
the calculations above we can see that we'd need a FMU ratio of 5.83:1, roughly
a 6:1 ratio. In this instance I recommend the 7:1 FMU with the use of the air
bleed valve to dial in your maximum fuel pressure.
I always recommend having your car tuned by professionals
on a chassis dyno for a safe air/fuel ratio of 11.0:1 to 11.5:1
while turboing the stock engine.
Fuel Pump
The stock fuel pump wasn't designed to ever exceed 70-80psi of fuel pressure
or deliver the volume of fuel that is necessary so an upgrade is in order. The
fuel pump is located inside the fuel tank which can be accessed simply by
removing the rear seat cushion and removing a service plate. Since the fuel
pressures required are so high, not just any aftermarket fuel pump will do. The
most widely recommended fuel pump used by 2G owners has to be the
WALBRO 255lph(liters-per-hour) pump assembly. Walbro makes 2 models
that are a direct replacement for our cars, one being the standard 255lph model
and the second being a 'high pressure' version. Both flow exceptionally well but
the standard model can't sustain the fuel flow needed at such a high fuel
pressure we are required to have with the FMU. The 'high pressure' model
(part # GSS-342) is up to the task, though we are still just squeaking by with our
fuel flow requirements at 8lbs. of boost. Honestly, the high pressure model is
the better candidate no matter what fuel system you plan on going with so I
recommend the high pressure model no matter what setup you decide to use.
The higher pressures the fuel pump has to achieve, the less VOLUME of fuel it
can deliver. The main reason you see people setting their turbo kits and fuel
systems to a maximum of 110psi has more to do with the fact that 110psi is the
fuel pressure where the amount of fuel flow begins to decrease dramatically. At
roughly 275-300hp, the fuel pump would need to deliver roughly between 18.8-
21GPH (Gallons Per Hour) of fuel. If you look at the chart on the right you will
see that you are just BARELY shy of producing the proper amount of fuel. Its a
little too close for comfort for most people so they opt to rewire the fuel pump to
supply a more consistent, higher voltage to the fuel pump. This CHART is at
the factory rating of 12 volts and the pumps are rated at a fuel pressure of
43psi. As the voltage supply to the fuel pump increases, so does its flow
capabilities. HERE is an example of how much can be gained by increasing
the voltage supply to a fuel pump. The factory wiring which powers the stock
fuel pump is sufficient for a stock engine but it isn't up to the task of powering
the new Walbro fuel pump.
The simple solution is to rewire the fuel pump like is shown HERE. My only
suggestion is DO NOT SOLDER DIRECTLY TO THE RELAY! EVER!
Soldering directly to a relay causes far too much heat to enter the super thin coil
wires inside which can be damaged and ruin the fuel pump over time. The
best bet is to get a RELAY SOCKET from Radio Shack and solder all
connections to the wiring on the socket. This generally will increase the fuel
pump voltage from 11-12 volts to 13.5-14.4 volts! At these voltages, you will
have just enough fuel for the FMU setup.
Fuel Injectors
The next risk is with the fuel injectors. Again, with such high fuel pressures
present, the fuel injectors simply cannot maintain the same spray pattern as
they can at the factory suggested fuel pressures. Not only does the spray
pattern suffer but the injector can be forced to stay open for longer durations
(duty cycle). A fuel injector is designed to run safely up to an 80% duty cycle.
After you exceed a duty cycle of 80% you run the risk of the fuel injector sticking
open which would basically pouring gobs of fuel into the engine continuously.
We tested the actual duty cycle of the stock injectors under the conditions
presented by the stock system and the FMU system and found that in both
cases the maximum duty cycle recorded was between 78-80%. The ECU is
designed to never exceed this limit (to prevent the possibility of injector failure).
Just because we are adding more air into the engine with the turbo kit doesn't
mean the ECU will keep trying to add fuel. The ECU has NO CLUE there is
more air! The 'MAP Sensor' and 'Throttle Position Sensor' are the 2 primary
signal sources which the ECU uses to calculate how much fuel is required
when driving WOT(wide open throttle). Once the MAP sensor reaches 0lbs. of
pressure....its maxed out, and since the gas pedal is to the floor its maxed out
too. As far as the ECU is concerned, you just floored a completely stock
engine.
The ECU is in open loop mode (oxygen sensor is not used and the air/fuel ratio
is controlled solely by a fuel map built into the ECU) once you exceed 80%
throttle position or a calculated load amount derived from multiple sensor
readings. While in open loop mode, the ECU is set to run a rather "safe", rich
air/fuel mixture mainly to prevent thousands of warranty issues from blown
engines that were running too lean. SInce they know its running overly rich at
80% duty cycle, there was no need to have any sensors monitor the air intake to
increase the duty cycle any further.
With that all said, you do not run the risk of your stock injectors getting stuck
open during operation. I definitely suggest replacing your stock injectors with
new injectors or having yours cleaned,blueprinted and balanced by a reputable
shop like RC Engineering. Cleaning services usually run about $100 for a set
of 4 injectors and the price includes new o-rings, a detailed before/after data
sheet and full ultra-sonic cleaning of your fuel injectors so they literally look and
perform better than new.
Things to Know
There are risks to using this setup which should be taken into consideration.
With fuel pressure exceeding 100psi, things begin to fail. The first item to fail
would be the incorrect choice of rubber fuel lines when installing the FMU.
Standard rubber fuel line cannot safely support these pressures so you must
use rubber fuel hose specifically used for FUEL INJECTION systems. It will be
labeled directly on the side of the hose so if you don't see it, its probably not
what you need. The most popular and safest bet is to use flexible stainless
steel braided fuel lines and fittings. Its rather inexpensive and looks and
performs far better than the standard rubber hoses.
Stage One Summary
All in all, the Stage 1system does a fair job of adding the additional fuel
needed. As long as you do not exceed 8lbs. of boost in this setup, it does
indeed work. What the system lacks is overall control of the fuel system, which
the other fuel stages address.
Pro's
Con's
Jamie Harvey
So its time to start preparing the sleeper for its destiny with the turbo gods.
What we need to focus on first is the most crucial piece of the puzzle, the fuel
supply. Its really easy to just slap a turbo onto your engine and to shove tons of
air down the throat of your 420A. Having the additional air is only half of the
equation and too many people focus on the turbo setup without taking the
same time and consideration when designing the fuel system to keep up with
the demands presented by the turbo system.
After lots of online reading, research and forum jumping, I noticed that there are
roughly five different stages that most 420A owners tend to use when
upgrading their fuel system:
- Stage 1: Standard FMU
- Stage 2: Super FMU
- Stage 3: Super FMU with Larger Fuel Injectors
- Stage 4: 8 Injector Fuel System
- Stage 5: Stand-alone Engine Management System
Next I will explain how Stage 1 works and try to point out the advantages and
disadvantages to this design.
The F.M.U.
The simplest way to add the additional fuel required is with a FMU . A FMU is
basically a second FPR(fuel pressure regulator) that is installed between the
stock FPR and the return fuel line heading back to the tank. As boost pressure
increases, the fuel pressure will increase above the set limit of the factory FPR
at an increment determined by the size of the FMU you are using. FMU's
generally are available in sizes ranging from 12:1, 10:1, 8:1, 7:1, 4:1, and 3:1.
The most commonly suggested size FMU to use on our car when using the
stock FPR and fuel injectors would be the 12:1 ratio unit (this isn't necessarily
the best choice, read on). What this means is that for every 1 lb. of boost
pressure, the fuel pressure will rise by 12psi above the static fuel pressure set
by the stock regulator.
With the stock FPR factory set to roughly 55psi static pressure (0psi of boost
present) and our system running at a maximum of 8psi of boost, that would top
out our fuel system at:
55psi + (12 x 8lbs. of boost) = 151psi!! Yikes!
In reality, it generally doesn't reach this high of a level due to pressure losses
from the stock fuel injectors having to be opened for such long durations and
the fuel pressure limits of the fuel pump. Most people have seen good results
with a maximum fuel pressure of around 105-110psi while running 8-9lbs. of
boost on an otherwise stock setup. With that being said, why don't people use
a 7:1 FMU instead?
55psi + (7 x 8lbs. of boost) = 111psi
This seems perfect so why does everyone suggest the 12:1 FMU? There are a
few reasons why. The biggest reason is simply for extra insurance. Most FMU
manufacturers will suggest this size because they honestly have no idea how
efficiently your engine responds to forced induction and there are too many
variables to consider with each customers turbo setup. All in all, this would be
a safe choice to suggest to the general public. Its better to have too much fuel
when running a turbo than it is to run too little. The problem with the 12:1 FMU
is that it isn't really regulating the fuel pressure if you are running more than
5lbs. of boost, its simply closing off the return line to the fuel tank. With just
about any aftermarket high pressure fuel pump, 100-110psi is the maximum
fuel pressure it can deliver while still delivering any significant volume of fuel.
Exceed this level and you are simply plugging the return line and reducing the
volume of fuel being delivered, not to mention you are stressing the HECK out
of your fuel pump!
The "Proper" Size F.M.U.
Okay, this is going to be a bit lengthy because I am about to explain this more
thoroughly than I have seen anyone else do, I apologize in advance. After
talking for countless hours with FMU manufacturers and Turbo kit
manufacturers for the non-turbo Ecipses/Talons, I have finally got down to the
truth about what size FMU is correct for our application.
The great thing about our car is there has been quite a bit of research and
development by major turbo kit companies, like Hahn Racecraft and Star
Performance. Thanks to them, we have a general idea of how efficiently our
engines respond to a turbo setup. Not only that, but we also have a target
range to start with for our maximum fuel pressures. Granted, the size and
efficiency of the turbo comes into play when fuel pressures are involved but
most people decide to use a turbo that produces roughly the same CFM range
as the turbos supplied in the Hahn and Star turbo kits. If you are going with a
much larger turbo than they offer....I sure hope you aren't using this type of fuel
system!
Back to the FMU situation. Like I mentioned earlier, at 8-9lbs. of boost on an
otherwise stock engine you would want to achieve a maximum fuel pressure of
roughly 105-110psi. This should provide a slightly rich fuel mixture, which is
good to prevent detonation (also the number one killer of most turbo engines).
When choosing an FMU you always want to aim a bit higher than your target
fuel pressure. If running 8lbs. of boost you would try to achieve 110psi so lets
figure out what size FMU we would need:
110psi - 55psi(maximum static fuel pressure of the stock FPR) = 55psi
So we need the fuel pressure to increase 55psi from 0lbs. of boost(static Fuel
Pressure) to our maximum boost pressure of 8psi.
Now divide the difference by the maximum boost pressure.
55psi / 8lbs. of boost = 6.875
So you need to increase the fuel pressure by 6.875psi for every 1lb. of boost
pressure. This is pretty darn close to a 7:1 ratio. Since each vehicle is different,
there are always slight variances in the maximum fuel pressures seen. With
that in mind, I would suggest the use of an 8:1 FMU when running 8-9lbs. of
boost. This would give you a maximum fuel pressure of roughly:
55psi + (8 x 8lbs. of boost) = 119psi
Vortech Engineering offers an air bleed valve HERE which you install inline with
the vacuum source to the FMU which allows you reduce your maximum fuel
pressure down a full 2:1 ratio. This will give you the ability to adjust your FMU
range anywhere from 8:1 down to 6:1 so you can dial in your maximum fuel
pressure for the best possible air/fuel ratio.
For people who think that this is too low of a ratio, just look at all of the users
who run the Vortech S-FMU unit. The maximum ratio it is capable of is 7:1 and
there are countless success stories of people who have used this setup for
many, many years with the stock injectors. People have recommended the
12:1 FMU because that is what some tech support guy told their friend, who told
their friend, who told their friend to use. Do you want the universal answer or
the one that pertains to your car? Hmm?
For anyone choosing to run only 5-6lbs. of boost, thanks to Hahn Racecraft we
know that a maximum fuel pressure of 85-90psi is generally needed. Using
the calculations above we can see that we'd need a FMU ratio of 5.83:1, roughly
a 6:1 ratio. In this instance I recommend the 7:1 FMU with the use of the air
bleed valve to dial in your maximum fuel pressure.
I always recommend having your car tuned by professionals
on a chassis dyno for a safe air/fuel ratio of 11.0:1 to 11.5:1
while turboing the stock engine.
Fuel Pump
The stock fuel pump wasn't designed to ever exceed 70-80psi of fuel pressure
or deliver the volume of fuel that is necessary so an upgrade is in order. The
fuel pump is located inside the fuel tank which can be accessed simply by
removing the rear seat cushion and removing a service plate. Since the fuel
pressures required are so high, not just any aftermarket fuel pump will do. The
most widely recommended fuel pump used by 2G owners has to be the
WALBRO 255lph(liters-per-hour) pump assembly. Walbro makes 2 models
that are a direct replacement for our cars, one being the standard 255lph model
and the second being a 'high pressure' version. Both flow exceptionally well but
the standard model can't sustain the fuel flow needed at such a high fuel
pressure we are required to have with the FMU. The 'high pressure' model
(part # GSS-342) is up to the task, though we are still just squeaking by with our
fuel flow requirements at 8lbs. of boost. Honestly, the high pressure model is
the better candidate no matter what fuel system you plan on going with so I
recommend the high pressure model no matter what setup you decide to use.
The higher pressures the fuel pump has to achieve, the less VOLUME of fuel it
can deliver. The main reason you see people setting their turbo kits and fuel
systems to a maximum of 110psi has more to do with the fact that 110psi is the
fuel pressure where the amount of fuel flow begins to decrease dramatically. At
roughly 275-300hp, the fuel pump would need to deliver roughly between 18.8-
21GPH (Gallons Per Hour) of fuel. If you look at the chart on the right you will
see that you are just BARELY shy of producing the proper amount of fuel. Its a
little too close for comfort for most people so they opt to rewire the fuel pump to
supply a more consistent, higher voltage to the fuel pump. This CHART is at
the factory rating of 12 volts and the pumps are rated at a fuel pressure of
43psi. As the voltage supply to the fuel pump increases, so does its flow
capabilities. HERE is an example of how much can be gained by increasing
the voltage supply to a fuel pump. The factory wiring which powers the stock
fuel pump is sufficient for a stock engine but it isn't up to the task of powering
the new Walbro fuel pump.
The simple solution is to rewire the fuel pump like is shown HERE. My only
suggestion is DO NOT SOLDER DIRECTLY TO THE RELAY! EVER!
Soldering directly to a relay causes far too much heat to enter the super thin coil
wires inside which can be damaged and ruin the fuel pump over time. The
best bet is to get a RELAY SOCKET from Radio Shack and solder all
connections to the wiring on the socket. This generally will increase the fuel
pump voltage from 11-12 volts to 13.5-14.4 volts! At these voltages, you will
have just enough fuel for the FMU setup.
Fuel Injectors
The next risk is with the fuel injectors. Again, with such high fuel pressures
present, the fuel injectors simply cannot maintain the same spray pattern as
they can at the factory suggested fuel pressures. Not only does the spray
pattern suffer but the injector can be forced to stay open for longer durations
(duty cycle). A fuel injector is designed to run safely up to an 80% duty cycle.
After you exceed a duty cycle of 80% you run the risk of the fuel injector sticking
open which would basically pouring gobs of fuel into the engine continuously.
We tested the actual duty cycle of the stock injectors under the conditions
presented by the stock system and the FMU system and found that in both
cases the maximum duty cycle recorded was between 78-80%. The ECU is
designed to never exceed this limit (to prevent the possibility of injector failure).
Just because we are adding more air into the engine with the turbo kit doesn't
mean the ECU will keep trying to add fuel. The ECU has NO CLUE there is
more air! The 'MAP Sensor' and 'Throttle Position Sensor' are the 2 primary
signal sources which the ECU uses to calculate how much fuel is required
when driving WOT(wide open throttle). Once the MAP sensor reaches 0lbs. of
pressure....its maxed out, and since the gas pedal is to the floor its maxed out
too. As far as the ECU is concerned, you just floored a completely stock
engine.
The ECU is in open loop mode (oxygen sensor is not used and the air/fuel ratio
is controlled solely by a fuel map built into the ECU) once you exceed 80%
throttle position or a calculated load amount derived from multiple sensor
readings. While in open loop mode, the ECU is set to run a rather "safe", rich
air/fuel mixture mainly to prevent thousands of warranty issues from blown
engines that were running too lean. SInce they know its running overly rich at
80% duty cycle, there was no need to have any sensors monitor the air intake to
increase the duty cycle any further.
With that all said, you do not run the risk of your stock injectors getting stuck
open during operation. I definitely suggest replacing your stock injectors with
new injectors or having yours cleaned,blueprinted and balanced by a reputable
shop like RC Engineering. Cleaning services usually run about $100 for a set
of 4 injectors and the price includes new o-rings, a detailed before/after data
sheet and full ultra-sonic cleaning of your fuel injectors so they literally look and
perform better than new.
Things to Know
There are risks to using this setup which should be taken into consideration.
With fuel pressure exceeding 100psi, things begin to fail. The first item to fail
would be the incorrect choice of rubber fuel lines when installing the FMU.
Standard rubber fuel line cannot safely support these pressures so you must
use rubber fuel hose specifically used for FUEL INJECTION systems. It will be
labeled directly on the side of the hose so if you don't see it, its probably not
what you need. The most popular and safest bet is to use flexible stainless
steel braided fuel lines and fittings. Its rather inexpensive and looks and
performs far better than the standard rubber hoses.
Stage One Summary
All in all, the Stage 1system does a fair job of adding the additional fuel
needed. As long as you do not exceed 8lbs. of boost in this setup, it does
indeed work. What the system lacks is overall control of the fuel system, which
the other fuel stages address.
Pro's
- Simple Installation
- Low Cost
Con's
- Extremely limited fine-tuning adjustments
- Taxes the fuel injectors
- Insanely high fuel pressures
- Robs potential horsepower
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