As I stated in the introduction, the goal of this book is not to make you an expert on building a monster modular engine. The goal is to help you get the engine in your chassis and make you aware of the options available for the project. The fuel system is a prime example because it can be set up many different ways. I could fill an entire book explaining it all. The engine builder and dyno data determine the ultimate choice on fuel systems (see Chapter 10). For more in-depth information on fuel systems and what works best for you, I recommend the book Designing and Tuning High-Performance Fuel Injection Systems by Greg Banish.
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While you can install and use carburetors on a modular engine, fuel injection is the preferred fuel system for most owners and swappers, and therefore, this chapter deals primarily with fuel injection. Always keep in mind, fuel injection works at higher pressures, and improper design can lead to leaning out the engine, which can lead to burning a piston or other damage.
Returnless versus Mechanical Return Line Fuel Systems
In a carburetor, the fuel bowl fills up with fuel, the needle is pushed into its seat, and it closes. The flow of fuel stops until the float lowers enough to re-open the seat. Carburetors run at about 5 to 7 psi, just enough to maintain fuel flow into the bowl. If there is a loss of fuel pressure, it isn’t noticeable until the bowl is empty.
Fuel injection works at pressures of 32 psi or higher, depending on the application, but you need to consider both the fuel rail pressure and differential pressure. Fuel rail pressure is the actual pressure inside the fuel lines, and differential pressure is the pressure working on the fuel injector at any time. Recognize that differential pressure can be different from rail pressure. When a naturally aspirated engine is at idle, intake manifold vacuum is present in the engine. The vacuum draws more fuel through the injector when it opens, increasing the differential pressure on the injector. With a forced induction system, pressure increases in the intake manifold as RPM increases. This pressure acts against the pressure driving the fuel through the injector and reduces the differential pressure on the fuel injector.
Ford used a fuel rail pressure regulator mounted at the end of the fuel rail up through 1998. The fuel pressure regulator system maintains fuel rail pressure with a spring and valve. These allow the regulator to open at a specific pressure and divert the excess fuel flow back to the fuel tank. By sensing the intake vacuum or pressure, it can adjust the rail pressure up or down to maintain the correct differential pressure across the fuel injectors.
A mechanical fuel regulator has one drawback. When fuel is pumped from the tank, it can be heated while passing through the engine compartment, and it can return to the tank at higher temperatures. The boiling point of gasoline can be as low as 90 degrees Fahrenheit (35 degrees Celsius). So it is easy for the fuel to turn into vapor, which can create more hydrocarbons and increase vehicle emissions levels.
In 1999 Ford elected to use a returnless system, in which an FRPS (Fuel Rail Pressure Sensor) regulates the fuel pressure. Mounted on the fuel rail, this sensor tells the PCM the fuel pressure at the engine. The PCM adjusts the voltage to the fuel pump to keep the fuel pressure in the required range. The FRPS also measures manifold vacuum/pressure to adjust the differential pressure. One of the big advantages is the elimination of some of the evaporative emissions issues listed above. One drawback to this system is that the fuel can sit longer in the engine bay and absorb heat, but the FRPS can sense this condition and compensate.
Aftermarket Fuel-Bypass Regulators
Externally mounted bypass regulators work similar to the Ford-mounted units, with a little more accuracy. They typically are designed to use AN-style or O-ring fittings. They should be mounted at the end of the fuel rail if possible, which means that you have one or two lines feeding the regulator after they have passed over the fuel injectors.
Which regulator you choose largely depends on how much fuel is required. In general, you should use pumps, regulators, and filters as a system from the same manufacturer because they are designed to work together.
Several builders opt for the Aeromotive 13129 series regulators as a good universal regulator. It features O-ring ports and a vacuum port that can be used for boost or intake vacuum. Fuelab’s 535 series regulators are compact to fit in tight spaces, and the Fuelab 529 series of electronic pressure regulators work with its Prodigy fuel pumps and reduce and maintain the return-line flow, which can reduce overheating of the fuel caused by constant pressure of the pump.
Single versus Dual Fuel Pumps
Ford typically installs dual fuel pumps on factory supercharged modular engines. Running two smaller pumps is better than running a big pump all the time because you can shut one down if needed. In most cases, a large single pump that runs at a constant voltage with a mechanical regulator and return line pumps more fuel to the engine than it requires. The excess fuel is returned to the tank, resulting in more vapors and heat, and in some cases, the pump may be louder.
Mounting the fuel pump in the tank reduces the chances of pump cavitation and starving the fuel system. The fuel also keeps the pump cool. When the pump is mounted externally, restrictions in the inlet tube can cause a drop in inlet pressure and allow bubbles to form and cause cavitation. The advantage to the external pump is that you don’t have to drop the tank should you need to access the pump, and the pumps are not limited to tank size or design.
An important thing to consider when choosing a fuel pump is that superchargers and turbochargers increase the amount of air going into an engine, requiring more fuel. Make sure to follow the manufacturer’s recommendation for fuel delivery.
Aftermarket Fuel Pumps
An aftermarket pump doesn’t care about the brand of engine it is supplying, so you have virtually an unlimited number of pump options. Some work with the Ford returnless design. The PA series of in-tank pumps from Tanks Inc. can be adapted to most fuel tanks and come with its own baffling, so no internal baffles are needed. The Aeromotive Phantom fuel pump is made to adapt to most non-EFI, non-baffled tanks and comes complete with a foam ring that acts as a baffle. The Phantom system can also be used with the 1999 returnless fuel system, as it can be adapted to the pulse-modulated output from the factory computer and fuel pump modulator. The Walbro GS series of pumps have been the standard upgrade for inline fuel pumps since the 5.0 pushrod engines, and work fine with the modular engine conversions.
Fuel Pump Voltage Boosters
As the fuel pump reaches 100-percent capacity when the engine is at wide-open throttle (WOT) and operating high RPM, it may not produce adequate fuel volume and/or pressure, which could cause the engine to lean out, resulting in damage. This is especially true with forced induction and nitrous, where additional fuel needs to be added as the engine RPM increases.
One alternative to using a larger fuel pump is to increase the voltage to the existing pump. Pumps are designed to work at 12 volts, but some manufacturers have designed their pumps to tolerate and operate at voltages of 20 volts or more. Increasing the voltage increases the output of a pump. By delivering this voltage when needed at WOT, a smaller pump runs cooler, and it can be used to power an engine that requires more flow when needed. Caution: increasing the voltage to a fuel pump not designed for higher voltage will likely result in damage to the fuel pump.
Because supercharging requires additional fuel, Kenne Bell has been on the front edge of voltage boosters for fuel pumps with its Boost-a-Pump line. Its systems open when needed at WOT and maintain accurate pressure flow. JMS FuelMAX V2 voltage boosters can increase fuel volume up to 85 percent and allow for user control of the ramp-up rates to correct and eliminate voltage spiking when the voltage is increasing.
Fuel Injectors and Rails
A fuel injector is nothing more than an electronic fuel control valve. The computer grounds the circuit to the injector and opens the nozzle, or pintle, for a selected amount of time to allow fuel to flow into the cylinder. A few terms you may hear about when selecting injectors:
In the United States, the fuel flow rate is measured in pounds per hour. A standard Coyote injector flows 24 pounds of fuel per hour at 43.5 psi (about 300 kPa) at 100-percent duty cycle; that means it’s open all the time. You need to determine the correct size of fuel injector for the engine’s fuel requirements (see formula below). Changing the size of the injectors may or may not have any effect on the performance of an engine. In fact, you could harm performance if you install the wrong size of injector. If the engine is not designed for the fuel delivery by the bigger injectors, hesitation or stumbling may result, or the computer monitoring the air/ fuel ratio may turn the fuel injectors on or off at a different rate, resulting in the same fuel delivery as a smaller injector.
The formula for calculating what size injectors you need is:
Flow Rate = Engine HP (at the flywheel) x BSFC (brake specific fuel consumption) ÷ 8 (the number of injectors) x .85 (maximum desirable duty cycle for the injectors)
This specification measures how long the injectors are open and closed. An injector running at 50-percent duty cycle is open and closed in equal parts. A street engine should not be operated at a duty cycle above 80 percent. If an injector operates at 100-percent duty cycle (open all the time), it is operating in a static mode, which can cause damage to the injector, and higher than 85 percent may mean it is trying to close while trying to reopen again in the cycle, which can cause erratic fuel delivery. Although injectors are tested at wide open (100-percent duty cycle) to test the flow rate, they should never be operated in this condition. Operating at a duty cycle greater than 80 percent indicates the injectors are too small for the application.
Impedance is the electrical resistance in the injector. This resistance is a result of the design of the electrical coil and materials used. Most factory injectors are high impedance for cost reasons. Most racing platforms use low-impedance injectors due to their ability to open and close faster.
Most aftermarket computers can control either, so it is not necessary to convert to low-impedance injectors if there is no requirement for their use.
Boosted versus Naturally Aspirated Engines
As previously stated, when you boost the engine and add pressure to the intake manifold, the increased intake pressure counteracts the fuel rail pressure in the injector and resists the fuel flow from the injector. As boost increases, you need to add an equal amount of fuel pressure to compensate for the boost resistance.
Injectors come in numerous flow rates and body shapes. Some intake manifolds have specific hard mounts for fuel rails, so fuel rail mounts may dictate the actual usable length of the fuel injector body. Take care to note that there are two types of connectors used in the different injectors on Ford engines: the JetRonic/Minitimer connector and the USCAR connector.
An in-tank pump either has a fuel filter mounted on the pump or a screen on the inlet. Inline pumps generally recommend an inlet filter to prevent damage to the pump, but using the wrong filter can also cause damage. A filter that is too fine can cause excessive restriction and cavitation if it’s mounted before the filter. To make sure the filter isn’t a bottleneck in the fuel path, use a filter with the same size openings as the fuel line, and the greater the surface area of the filter, the better the fuel flow. A small, screen filter is not recommended because it clogs faster, resulting in damage. Some Ford applications have a non-serviceable fuel filter mounted on or in the pump. Although the factory Ford filters are inexpensive and work in some street applications, as performance increases you should look toward micron specific filters for better filtration. Aeromotive sells a complete line of inline filters that filter between 100 down to 10 microns and come in AN or O-ring, fitting from -6 to -10 sizes.
EFI conversions for classic cars have become more popular and, as a result, retrofit fuel tanks are readily available for many models. The key factor when selecting a fuel tank is to get one with internal baffling. Baffling in the tank prevents a sudden slosh of fuel away from the pickup, as under hard acceleration or cornering. This can cause the fuel pump to draw in air, or cause cavitation, which results in pressure problems with the fuel system. When using an in-tank pump and return line, avoid the return port dumping directly on or near the pump, as this can dump heated gas into the pump suction screen, potentially resulting in premature pump failure.
Hoses and Fittings
Hoses and fittings need to be matched in size to the outlet of the pump so they do not create a restriction in the fuel line. Fittings and hoses should have radiused bends and no sharp angles. Rubber hoses for carbureted and fuel-injected systems have different specifications, so make sure all the flexible hose is fuel-injection spec. Fuel lines can be steel, aluminum, or plastic, braided or woven hose.
The EVAP system takes vapors from the gas tank and flows them into a charcoal canister, where they are stored until they are pulled into the intake manifold and burned. This not only helps the efficiency of the engine by burning fuel vapors that would typically be lost, but it lowers hydrocarbon emissions.
The pressure in the fuel tank increases or decreases as fuel heats and expands or cools and contracts. Before emission control systems were put in place, these gases were vented into the air and replaced with the atmosphere through a vented gas cap. An emissions system draws the vapors from the tank but also replaces the vapors with air through a valve. The EVAP maintains a specific pressure level in the tank, and when the gas cap is left off the filler tube, the computer generates an error code.
When the valve or gas cap fails, vacuum or pressure can build up in the tank. Pressure can cause the gas cap to vent fuel when opening, and vacuum can counteract the fuel pump’s ability to draw fuel from the tank. Both conditions can cause the gas cap to become difficult to remove.
In some racing and some regional situations, the EVAP system can be eliminated, and along with it the lines and hardware needed for it to operate. Most aftermarket fuel tank manufacturers do not have provisions for the EVAP system. To run the EVAP, it may be necessary to retrofit a tank that already has this provision, or modify an aftermarket tank. If the EVAP system is not used the PCM needs to be programmed to compensate.
Drive-by-Wire Gas Pedal
In 1969 Ford started using cable-operated throttle controls on some models, continuing to use cable systems until the throttle-by-wire systems went into production in 2005. For Mustangs and Cougars prior to 1969, the 1969 gas pedal can be adapted to run a cable throttle. Depending on the computer control system selected, it may be necessary to convert back to a cable-operated throttle pedal.
Swap Spotlight: Factory Five Cobra
Factory Five has never been a company to rest on its laurels. Before it entered the aftermarket roadster market, parts and kits for the aftermarket builders were kind of hit or miss, and based on technology that was slowly fading into the past. Factory Five hit the market with technology, commonsense, and modern design. Its Mk4 roadster is now the best-selling component car in the world, and Factory Five has no plans to slow down after 20 years.
In 2015, the company celebrated its 20th anniversary in the marketplace and decided to mark the occasion with a mark, Mk4, that is. This would be no ordinary roadster build: this Mk4 would be equipped with a full complement of custom items to denote the special car and would be limited to 20 units of production, which went quite quickly. With Factory Five’s commitment to pushing technology for component car manufacturing, the logical choice for the engine in its car was the new Ford Performance 5.0 crate engine.
Along with the Coyote engine, Factory Five optioned out the anniversary cars with a long list of features, including special 20th anniversary badging, custom powder coating on the frame and footwells, polished stainless-steel side pipes and front and rear bumpers, and a custom chrome driver’s rollbar with body grommets. The 2015 Mustang Mk4 was equipped with the new independent rear suspension. Its fully adjustable tubular front control arms are complemented by Koni custom coil-over shocks on all four corners. Massive Wilwood nickel-plated six-piston calipers up front and dual-piston calipers out back are used to stop the 13-inch drilled and slotted Wilwood rotors. Wheels are custom 18-inch Halibrands designed specifically for the car, with 18 x 11–inch out back and 18 x 9–inch up front. Special GPS speedometer gauges with the 20th anniversary logos were installed, and the kits were optioned with plenty of add-ons such as leather seats and padded dash and door panels.
The engine is a Ford Performance Crate Coyote 5.0 fitted with a Cobra Jet intake manifold and throttle body. A Ford control Pack computer is installed with HP tuners. This crate engine pushed 404 hp through the rear Halibrands. The transmission is a time-proven Tremec TKO 500 5-speed.
While the special-edition Mk4 anniversary cars were claimed right away, Factory Five has full parts lists and instructions for installing Coyote engines into its cars and has done the legwork and documented what you need to know to perform the conversion. Factory Five’s online forum is the place to go if you are looking to customize your build even further. Factory Five lists specific parts you should look at that it has confirmed work with its kits. The instructions for its component cars are complete even down to individual hose fittings.
Although it is too late to get in on the 20th anniversary Mk4, there is sure to be another impressive build coming up for its next anniversary. Until then, Factory Five has done all the legwork for you, so you can have an amazing roadster with reliable, powerful modular engine technology under the hood.
Written by Dave Stribling and Posted with Permission of CarTechBooks
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