Cutting Edge Fuel Injection Systems & Components For Over 65 Years

Mechanical Fuel Injection Technical Instructions and FAQs

MFI Installation Instructions

Fuel Injection Installation and Idle Adjustment:
The HILBORN fuel injector is completely assembled, flow tested, and ready to install. The idle mixture and idle speed are factory set but will probably require some adjusting. The idle speed is adjustable by loosening the locknut on the throttle stop screw and turning the screw to open or close the throttle. The idle mixture is controlled at the fuel metering valve on the injector. The linkage between the valve and the throttle shaft consists of a threaded turnbuckle, one end has a right-hand thread and the other has a left-hand thread. Loosen both locknuts and turn the turnbuckle. To richen the idle, adjust the turnbuckle so that the arm on the metering valve moves in the open throttle direction. To lean the idle, reverse the procedure; one half to one turn should be ample. Retighten the locknuts. As previously stated, this adjustment is factory set and need not be tampered with excessively. On models where the injector consists of two castings, fasten the castings to the heads and then adjust the length of the hex linkage rod that connects them together until both throttles are closed down on the throttle stops. This is very important to obtain a good idle and should be repeated with the engine running. Another way is to loosen the allen screw on one of the arms of the cross link, move both throttle shafts to the closed position and tighten the allen screw.

Butterfly Adjustment:
Install the injector and the fuel pump onto the engine. If the throttle shows any sign of sticking, loosen all the butterfly screws and tap the shaft back and forth, then all the way to one side. Tap halfway back to center to relocate the line and re tighten the screws. Adjust the butterflies when the engine is hot, except when running methanol, adjust them when the engine is cold. Use thin intake gaskets where possible since thick gaskets may cause the throttles to stick.

Mixture Control:
The main mixture control is the jet inside the by-pass container, the #4 By-Pass Valve. To change the mixture, unscrew the cap from the container, and change the jet in the cavity in the cap. Increasing the size of the jet leans the mixture. This container also includes a 4-sided poppet valve and a spring. If the poppet is removed, be sure it is replaced with the pointed end away from the spring and toward the pump. Operating fuel pressures and recommended jet sizes are approximate starting points only. These pressure readings will be attained only at 6000 RPM and with the throttle fully opened. Do not hesitate to use other jet sizes when conditions warrant.

Fuel Filter:
Do not, under any condition, attempt to run the engine without installing a high quality fuel filter. We strongly recommend the screen type filters and advise against using paper, ceramic, or laminated metal filters. HILBORN manufactures several types of screen filters. The filter may be mounted anywhere on the intake side of the pump. In addition to the fuel filter, a safety screen is also incorporated into each of the individual injection nozzles to catch any stray particles of dirt. These screens may be cleaned by removing the nozzles and blowing out any foreign material, however, care should be taken to avoid puncturing the screens.

Starting the Engine:
Since this is a pressure system, it is necessary to have some degree of fuel pressure to start the engine. If pushing or towing the car is employed, sufficient pressure will be obtained and starting will be no different than with a carburetor. However, it may be necessary to prime the engine when using a starter. If an electric pump is used, do not install it in the main line running between the fuel tank and injector pump since the capacity of these pumps is too small for fuel to pass through. Hook the electric pump on a side branch line discharging into the injector pump outlet line. Very little pressure is required…. just enough to start the fuel dripping from the nozzles will give a quick start. Hold the throttle fully open while priming and then close it COMPLETELY SHUT during the actual starting operation. This eliminates the risk of fire. After the engine is running strong, shut off the electric pump if one is used. Once the engine has been running, the fuel lines will be filled and this procedure probably will not be necessary on any of the succeeding starts. However, for a fast, sure start, it is recommended. On all starts, hold the throttle fully open for a few seconds while the engine is turning, then switch on the ignition. This facilitates bleeding the air from the system. If the fuel pump is mounted below the fuel tank level, it will be primed automatically.

Ram Tubes:
We strongly recommend the use of ram tubes on all models of our injectors. Horsepower gains of about 5% to 10% are average for a system with ram tubes. HILBORN stocks a variety of styles in many I.D. sizes and lengths.

Fuel Pump Installation:
All HILBORN fuel pumps have grease packed bearings so no additional lubrication is required. We recommend the following inlet hose sizes for fuel pump installations. Do not use smaller sizes. Pump Model PG250, size #5 use 1-1/4″ hose. Pump Model PG175B, sizes #2, #4 use 1″ hose. Pump Models PG150C & PG150D, size #1 use 3/4″ hose. Pump Models PG150C & PG150D, sizes #S0, #0, #00 use 1/2″ hose

Fuel Pump Rotation:
To change the rotation of the pump, remove cover bolts and dowel pin. Move the pin 180 degrees to the opposite hole and replace the lid. CAUTION: Sometimes this change results in a tight pump. If so, do not attempt to run the pump! We recommend that it be returned to our factory for correction.

CAUTION: Avoid corrosion on magnesium castings:
Many of the HILBORN fuel injectors are designed with magnesium castings. Due to the very reactive nature of magnesium in the presence of water or methanol, we highly recommend special attention to these units. At the end of each race day, remove the nozzles and blow out the nozzle cavity and passageway with air to thoroughly remove any liquids. DO NOT allow liquids to stand in the injector overnight. Failure to keep the casting dry may lead to corrosion! After operating the engine on fuel containing any of the nitro-paraffin series such as nitro methane, flush the entire fuel system with a mixture of gasoline and oil. Do not allow these fuels to stand in the injector overnight as they are damaging to rubber.

Mechanical Fuel Injection Overview

A mechanical fuel injection system from Hilborn includes the manifold, nozzles, barrel valve, and hoses. The main jet, housed in the primary bypass valve, is also included along with 2 additional jets, or pills. To complete the system, you will need ram tubes, fuel pump, fuel filter, fuel shutoff valve and, possibly, a hi-speed bypass valve. If Hilborn cannot supply a fuel pump drive, you will need to fashion a drive for the pump to run at 1/2 crankshaft speed.

Using your supplied engines specs, racing venue, car characteristics, etc., we will flow the entire system. This provides a very good starting point but tuning will be required to optimize the injection system. A mechanical system is really quite simple, but needs to be tuned to the current weather conditions.

There are 4 main parts to a mechanical system:

  1. Fuel Pump
  2. Fuel Nozzles
  3. Main Jet (or pill)
  4. Barrel Valve

Since this is a constant flow system, fuel is supplied to the engine continuously. As the pump spins, the restriction in the system (set by the nozzle and main jet) develops pressure and, therefore, fuel flow to the engine.

The nozzle size is picked to deliver enough fuel at WOT for your engine, while the main jet is used to adjust the amount of fuel allowed to return to the tank, setting the actual fuel curve. This is exactly opposite of a carburetor.

The barrel valve acts like a fuel shutoff, controlling the amount of fuel for idle and transitional fuel to WOT. The barrel valve also works in conjunction with the secondary bypass valve for better part throttle fuel control.

At higher RPM the fuel pump will produce more pressure and volume than the engine can use, so a hi-speed bypass (or cutoff) is required.

Operating Tips

These operating tips and suggestions are the result of experience gained by years of running under varied conditions.

  • Due to the extreme clean-burning of finely atomized fuel, spark plugs generally take a long time to show any color. Do not change the mixture because of plug readings based only on a few laps. Pay more attention to the indications on the tops of the pistons, if visible, than to the plugs.
  • If the system does not operate correctly, disconnect the nozzle hoses, remove nozzle caps and blow through the nozzles with air pressure. If this procedure does not solve the problem, we recommend sending the injector, fuel pump and by-pass valve to our factory for testing and/or repair. When returning the unit, please supply all pertinent information such as the cubic inch of the engine, the type of fuel being used (gas, alcohol, or percentage of nitro) and manifold pressure if supercharged.
  • Do not allow running low levels of fuel in the tank as it will wash away from the pickup in the tank when the car is in the turns. The resulting gulp of air sucked into the system will give a momentary misfire in the engine. This is the first warning when running low on fuel.
  • Avoid tampering with the adjustments continuously. The unit is factory set and ready to run as received. Simply install the injector, select the desired starting by-pass jet and go out and race.
  • Shut the fuel off when the engine is not running to keep the nozzles from dripping. A shut-off valve should be installed on the outlet side of the fuel pump.
  • When the car has been left standing with the engine hot, you may notice that the throttle has become a little tight. This is due to expansion of the aluminum casting as it picks up heat from the engine. When the engine is started, the fuel spray cools it down and the throttle will free up immediately.
  • Extreme care should be taken to keep dirt from getting past the fuel filter and plugging a nozzle. Whenever the fuel lines are disconnected, tape up the openings immediately. Also watch for dirt in the threads of fittings when installing the pump and filter. Too much emphasis cannot be placed on the need for cleanliness.
Can I run a HILBORN mechanical fuel injector on a street car?

A Hilborn mechanical injector is classified as a constant flow system and was designed to operate at WOT under load. As a constant flow system, pressure and volume are controlled by the main jet, or pill, along with pump speed (engine rpm) and nozzle size. The barrel valve, which controls idle fuel and transitional fuel from idle to WOT, can be compared to a ball valve much like the one that turns off the water in your house. The basic design and lack of fuel control of a barrel valve does not allow us to control the fuel at part throttle especially no load part throttle. If you consider the fact that an engine’s fuel requirements are based directly on load, and that we can have many different loads at different rpms all at the same throttle angle, the lack of fuel control for street applications becomes apparent. A mechanical system does not employ enough fuel control in the operating range where you drive your street car and, therefore, is not recommended for street use.

Of course we have all heard the stories of mechanical system working on the street but few if any actually worked correctly. The use of a dial-a-jet, additional bypass valves, and home center ball valves have all been used to provide fuel control for adequate street use, but fall far short of the fuel control required as part throttle load is constantly changing. The constant manual adjustments needed, as one guesses the current fuel requirements of the engine, leaves very little time to actually drive the car and, at best, is incredibly inaccurate. Blown applications appear not to be as affected by the lack of fuel control of mechanical injection, possibly due to the load placed on the engine to drive the blower, but is still not recommended for those looking for the best all around drivability.

The use of alcohol helps because of it’s large tune-up window, but fails to provide drivability due to loading up, mileage (in gallons to the mile) and severe oil dilution. Claims from those that run injected engines on stands or dyno’s stating they can make mechanical injection streetable, are unable to simulate a fraction of the different part throttle load scenarios your engine will see, nor provide the required fuel control. Interestingly enough, engineers have devised a way to electrically control these valves and bypasses…it’s called electronic fuel injection.

NOTE: Our products are not legal for sale or use on emission controlled vehicles.

How to avoid corrosion on magnesium castings

Due to the very reactive nature of magnesium in the presence of water or methanol, it is extremely important to keep the injector casting dry! Do not allow liquids to stand in the injector overnight. Both magnesium and aluminum injector systems should be kept clean. After racing, remove nozzles and blow out the entire unit and nozzle chamber with air.

How to set the metering valve

Set injector to wide open throttle. As pictured in the Metering Valve Schematic, the distance “X” between the center of the rod-end bearings is equal to the distance “Y” between the center of the throttle shaft and the center of the metering valve rotor (#54 shown). Note that the inlet fitting on the block is off-set to one side. Adjust the rotor so that the number is located on the wide side of the off-set. Tighten arm on the rotor and the throttle shaft.

metering_valve

How to adjust the metering valve

Since the idle mixture is controlled by the metering valve, the purpose of adjusting is to achieve a richer or leaner idle condition. The linkage between the valve and the throttle shaft consists of a threaded turnbuckle, one end has a right-handed thread and the other has a left-handed thread. Loosen both locknuts and turn the turnbuckle. To richen the idle, adjust the turnbuckle so that the arm on the metering valve moves in the open throttle direction. To lean the idle, reverse the procedure. One half to one turn should be ample. Retighten the locknuts.

How can I loosen a stuck barrel valve rotor?

Use penetrating oil (such Kroil) to loosen the rotor. Once free, remove the rotor from the barrel valve and position it in a drill press. Lightly polish the rotor with 600 grit sandpaper. Clean and oil the barrel valve before reassembly.

Do I need to use a mechanical fuel pump with mechanical fuel injection or can I substitute an electric pump?

Typically spinning at half engine speed, a mechanical pump increases system volume and pressure according to increases in RPM. The varying volume and pressure from the pump is tailored to fit the fuel demands of the engine, from idle to wide open throttle, with the use of pills (jets), a barrel valve, and assorted bypass valves. Because of this, the constant pressure of an electric fuel pump is not suitable with mechanical fuel injection.

Which fuel pump should I run?

The first digit of the serial number stamped (not cast) into HILBORN pump castings indicates the pump volume. The following list is a guide to help you select the correct pump size for your fuel requirements:

PG150 series

size #00 – Extremely small engines such as motocycles.
size #0 – Medium size engines, 200″ to 360″, running gas or methanol. Use with carburetors or small turbo engines.
size #S0 – (Super-0) Medium size engines, 360″ to 410″, running gas, methanol, or small amounts of nitro.
size #1/2- Same as #S0, just a higher pump volume.
size #1 – Large engines on gas and small amounts of nitro. Also for blown engines on gas, methanol, and small amounts of nitro.

PG175 series

size #2 – Large engines with high percentages of nitro and blown engines on methanol.
size #4 – Very large engines, high percentages of nitro, and blown engines on nitro.

PG250 series

size #5 – Largest pump volume. Very large engines on nitro. Also for turbo or supercharged engines.

How can I identify the rotation of my Hilborn fuel pump?

Position the pump so the inlet is on your right and you are looking at the cover plate end of the pump. If the small dowel pin in the cover is at the top 12 o’clock position, it is a front cam drive rotation. If the pin is at the bottom 6 o’clock position, it is a belt drive or rear cam drive rotation.

How to change rotation of the fuel pump?

Remove the cover bolts and dowel pin. Move the pin 180 degrees to the opposite hole and replace the lid. Caution: Sometimes this change results in a tight pump. If this occurs, do not run the pump, but return it the factory for correction.

What difference does ram tube length make?

IR manifolds are unique in that changes to intake runner length are easily achieved. Changing this length can have a profound effect on where the engine makes idea power for your particular combination. In general, shorter ram tubes will provide more top end power at the expense of low speed torque, while a taller ram tube will increase low speed torque while losing some top end power.

Racing Applications:

Racing applications involving light-weight cars with high revving engines, such as FED or Jr. dragster, will typically employ a shorter ram tube to move the available power band to the higher RPM. Heavier applications such as door cars, or other racing venues that involve getting on and off the throttle will typically use a longer ram tube to achieve a balance of power throughout the operating range.

Street Applications:

With street applications, many use the ram tube as a focal point. Whether you want them sticking out of your hood, or under the confines of a stock hood, length plays a critical function aesthetically. This typically means that a compromise of sorts has to be made with respect to the ideal ram tube height for that particular engine combination. But what we have found is that the torque generation of an IR manifold is so much better than that of a common plenum manifold, that for most street applications ram tube height has little bearing on performance. So put the ram tube height where it looks the part and enjoy the additional torque regardless of that height.

Ideal Ram Tube Height:

What is the ideal ram tube height for my combination is a common question we get but is very hard to identify. Sure, there are numerous computer models available along with dyno testing which are all popular tools to help identify ram tube height. But even with these tools at our disposal, they have the inability to factor in all of the dynamic conditions of a race car. It is only through track testing that the ideal ram tube height can be determined.

The Ram Tube Bell:

At the top of a ram tube is the bell, and this is where all the magic begins. It has been identified on Indy car engines that the entrance speed at the bell of the ram tube exceeds the speed of sound which would not be possible without a properly designed bell. The bell provides the proper transition of the air into the ram tube which is an important process for the high air speeds generated by an IR manifold. We would like to suggest that the bell not be removed from the ram tube if at all possible.

The Primary By-Pass Valve

The Primary By-Pass Valve supplied with your Hilborn Injector serves two purposes. First, as a restriction in the system to help ease starting and, secondly, to house the Main Jet.

For Starting:

Remembering that a constant flow system needs a restriction to develop pressure, the spring and poppet valve located in the Primary By-Pass effectively block off the main jet in order to help develop pressure during cranking when pump speed, and therefore pressure, is very low. Springs for the poppet valve are available in 3 different gauges, allowing us to tailor the amount of fuel needed for each application. Most gasoline applications will use a .016 gauge spring (1.5 pounds of pressure), while alcohol applications will use either a .020 or .024 gauge (3 pounds or 5 pounds of pressure). Regular inspection of the poppet valve for cracks and dirt is recommended for proper operation.

Housing the Main Jet:

The Primary By-Pass valve also houses the Main Jet, or pill. The Main Jet controls the amount of fuel the engine will receive at all RPM ranges, along with setting the fuel curve at WOT. The larger the main jet, the more fuel is returned, and the leaner the mixture. A smaller main jet will, therefore, richen the mixture. The inlet side of the main jet is identified by a stamped number, along with a chamfered edge, and should be installed inside the Primary By-Pass with both of those visible.

Installation of the Primary By-Pass Valve:

The body of the Primary By-Pass is marked with an arrow along with a #4. The arrow should point to the fuel tank or, as an option for alcohol applications only, to the inlet side of the fuel pump. For applications with long fuel lines, such as door cars with the tank in the trunk, please consult the factory for recommendations. See the Installation Schematic for location of this valve in the fuel system.

The Secondary By-Pass Valve

The Secondary By-Pass Valve is used primarily for applications that get off and on the throttle at high rpm, such as sprint cars or applications with very low stall speed convertors. If the throttle is lifted to an idle suddenly at high rpm, the pump will continue delivering large quantities of fuel since the engine rpm is still high. Without the Secondary By-Pass, one can experience stumbling or excessive fueling at part throttle. With the Secondary By-Pass, this unwanted fuel is returned to the tank, and the system maintains the preset pressure.

Much like the Primary By-Pass, the Secondary By-Pass uses a poppet and spring arrangement, along with shims to help set the required pressure. Tailoring the pressure is accomplished with different spring tensions and shim combinations. The greater the tension on the poppet valve, the higher the pressure in the system.

Since fuel flow is controlled mechanically by the metering valve, any open throttle position of 25 degrees or more will automatically shut off the Secondary By-Pass. This eliminates the possibility of a lean condition when the throttle is open.

Installation of the Secondary By-Pass Valve:

The body of the Secondary By-Pass is marked with an arrow and the letter “S”. It connects directly off the metering valve with the arrow pointing toward the fuel tank. See the Installation Schematic for location of this valve in the fuel system.

The Hi-Speed Cutoff Valve

The Hi-Speed Cutoff is an optional valve that controls the higher rpm fuel curve of alcohol fuel engines that exceed 6500 rpm.

There is a certain point where the fuel pump output exceeds the required fuel flow of the engine. This typically starts to happen at 6500 rpm. Increasing the size of the main jet to return this additional fuel will leave the fuel curve very lean in the lower rpm. The Hi-Speed Cutoff is designed to remove this additional fuel without affecting the lower rpm fuel curve. Without the Hi-Speed Cutoff, the engine will seem to “lay-over” and stop accelerating as engine rpm’s rev past the 6500 rpm range. Gasoline engines will attribute this to a lean condition but with alcohol the condition is reverse, indicating a rich condition. Using a Hi-Speed Cutoff corrects this high rpm rich condition by bypassing unwanted fuel to the tank, restoring correct engine acceleration.

The Hi-Speed Cutoff uses a poppet and spring arrangement, along with a combination of thick and thin shims to set the required pressure. Tailoring the pressure is accomplished with different shim combinations. The greater the tension on the poppet valve, the higher the pressure in the system. When changes to the main jet in the Primary By-Pass Valve are made, a corresponding change should be made to the Hi-Speed Cutoff. For example, if the main jet is richened .005 (smaller orifice), one thin shim should be added to the Hi-Speed Cutoff, while a thin shim should be removed for every .005 you lean out the main jet.

Installation of the Hi-Speed Cutoff Valve:

The body of the Hi-Speed Cutoff is marked with an arrow and the letter “C”. It connects directly off the fuel pump with the arrow pointing toward the fuel tank. See the Installation Schematic for location of this valve in the fuel system.

Leakdown Metering Valve
  1. Connect the leak tester to the top of the metering valve block.
  2. If the metering block has a brass secondary by pass fitting, cap it off.
  3. Close throttle to idle.
  4. Plug in the leak tester and read leakage through metering block.
Leak Tester Instructions

The HILBORN leak tester is a cylinder leak tester as well as a fuel injector leak tester. Hoses and spark plug adapters are provided for both uses. The large #H6 hose attaches to the metering valve, while the smaller #H3 hose is for the nozzles.
To operate, install an inlet air fitting (not supplied) of your choice and supply the gauge with at least 80 psi. Turn back the regulator knob to ZERO on the gauge. Attach #H6 hose to the metering valve or spark plug adapter. Plug in a quick-disconnect adapter. Leakage will read on gauge.
NOTE: When checking the metering valve assembly, the “S” secondary by-pass valve must be capped off. Leakage is always read in the idle position.

Cleaning and off-season care instructions

Fuel Injector:

While opening and closing the throttle, blow air through the metering block to clear fuel from lines. Squirt some lite oil into the metering block. Once a year apply a drop of oil along the throttle shaft rub areas to keep it moving freely. Store the fuel injector in plastic.

Fuel Pump:

Squirt some lite oil into the pump and turn it over until it runs out the other side. Store in plastic.

Nozzles:

Clean nozzles by soaking them in solvent or gas and blowing them out with air. Nozzles can be checked for flow using a leak tester.

Fuel Cell:

Check the vent assembly and keep it clear of any blockage. Your tank must be properly vented when using fuel injection.

Manifold Adjustments

For correct operation of your Hilborn injector the manifold will need to be tuned. This includes linkage and butterfly adjustments. If the injector is removed from the engine after being tuned, the process will need to be repeated. Although injector linkage is preset at the factory, adjustments will need to be performed after installation. Three piece injectors, by nature of their design, will need to be adjusted before initial startup and when warm.

Adjustments should be made in the following order:

  1. Centering Butterflies
  2. Hex Link Adjustments
  3. Butterfly Arc and Adjustments
  4. Advanced Tuning

The first three adjustments will be performed with the ram tubes, throttle linkage and return springs removed. After you are satisfied with these adjustments, reinstall the throttle linkage, return springs and set idle speed. Recalibration of the TPS may be required. The fourth and final adjustment will then be performed. All adjustments should be performed with the engine at operating temperature.

Centering Butterflies (Stack Injectors) :
This operation verifies the butterflies are centered in the bore which removes the risk of sticking along with ensuring that the butterflies are in a fully closed position for the arc adjustments and for adequate idle speed control.

  1. Loosen lock nuts and back out idle stop screws on both ends of the injector.
  2. Identify the hex link that runs to either side of the injector and the bronze throttle arms.
  3. Loosen the allen head pinch clamp screw on only one bronze throttle arm.
  4. Loosen all the butterfly screws on one side of the engine.
  5. Lightly tap the butterflies closed with your finger while lightly sliding the throttle shaft back and forth against its’ stops.
  6. Center throttle shaft side to side. Tighten butterfly screws using caution not to over tighten.
  7. Perform same adjustments on other side of engine.
  8. Tighten the pinch clamp screw on bronze throttle arm.

Centering Butterflies (Blower Hat or Scoop Injectors) :
This operation verifies the butterflies are centered in the bores, which removes the risk of sticking along with ensuring that the butterflies are in a fully closed position for the arc adjustments and for adequate idle speed control. No other adjustments are required for hat or scoop injectors.

  1. Loosen lock nuts and back out idle stop screws on both ends of the injector.
  2. If your injector is electronic, do not loosen the pinch clamps that control the TPS linkage or improper function of the TPS may result. If you have upset this factory adjustment please call the EFI tech line.
  3. Loosen all the butterfly screws.
  4. Lightly tap the butterflies closed with your finger while lightly sliding the throttle shaft back and forth against its’ stops.
  5. Center throttle shaft side to side. Tighten butterfly screws using caution not to over tighten.

Hex Link Adjustment:
This adjustment verifies the hex link, along with the bronze arms, is at the optimal starting point for the butterfly arc adjustments.

  1. Loosen lock nuts and back out idle stop screws on both ends of the injector.
  2. Identify the hex link that runs to either side of the injector and the bronze throttle arms.
  3. Verify starting hex link length. The ideal starting length of the hex link is to make the centers of the heim joints the same center dimension as the butterfly shafts. An eyeball adjustment is all that is required at this time. NOTE: One side of the hex link will have a groove around the outside of the hex link; this to identify a left hand thread.
  4. Verify correct bronze arm angles by opening the throttle from idle to wide open, making sure the tip of the bronze arms are split on either side of 12 o’clock with relation to the butterfly shafts. In other words, idle will be at 10 o’clock, half throttle at 12 o’clock, and wide open will be at 2 o’clock. If not, loosen the two pinch clamp screws on the bronze throttle arms and adjust as necessary.
  5. Verify that both sets of butterflies are in the fully closed position by loosening one bronze throttle arm, allowing the butterflies to fully close. Tighten the pinch clamp screw and begin butterfly arc adjustments.

Butterfly Arc and Adjustments:
Insuring the butterflies on each bank are opening at the same rate is critical for correct throttle tip-in and part throttle drivability. The use of feeler gauges for adjusting the hex link for correct engine “tone” side to side will not correctly set the butterfly arc, and will result in a rich/lean condition on each side of the engine and poor drivability.

  1. Two pieces of round stock are required for gauging. Verify the gauging that you will be using to be within .001 of an inch from each other. Two philips head screw drivers from the same manufacture or socket extensions are ideal.
  2. Insert gauge #1 between the center of the throttle blade and wall of injector making sure that the gauging material stays in contact with the machined portion of the throat. While supplying light pressure with your finger to hold the butterfly against the gauge, insert gauge #2 between an open butterfly on the other side of the engine. If gauge #2 has a light drag without opening the butterfly against gauge #1, the arc is correct, remove gauging and proceed to “Final Tuning”. If gauge #2 is either loose or tight, see “Butterfly Arc Adjustments” for further adjustments.

Butterfly Arc Adjustments:

  1. Remove gauging from the injector.
  2. Identify the hex link that runs to either side of the injector and the bronze throttle arms.
  3. Loosen lock nuts on both sides of the hex.
  4. Either lengthen or shorten hex link 1/4 to 1/2 of a turn.
  5. Lightly tighten the lock nuts on the hex link.
  6. Note: The following MUST be completed or the adjustment will not be correct. Loosen the allen head pinch clamp screw on only one bronze throttle arm, lightly tap the butterflies closed on either side of the injector and tighten the pinch clamp screw.
  7. Insert gauge #1 between butterfly and wall of injector. While supplying light pressure with your finger to hold the butterfly against the gauge, insert gauge #2 between an open butterfly on the other side of the engine. If gauge #2 has a light drag without opening the butterfly against gauge #1, the arc is correct, proceed to line 9.
  8. If gauge #2 is closer to the ideal drag, repeat steps 4 thru 8 until correct spacing is accomplished. If gauge #2 identifies you are moving away from the ideal drag, reverse the direction you are turning the hex link and repeat steps 4 thru 8.
  9. Without introducing bind in the heim joints, fully tighten hex link lock nuts.

Final Tuning:
Final tuning, or balancing of the butterflies insures that each cylinder is performing the same work at idle and at part throttle. When accomplished, your engine will start and idle extremely well. For EFI applications, this step will ensure there is a good exhaust note and provide the best in drivability and engine acceleration. For Mechanical/Racing applications this step will ensure that all cylinders are at the correct temperature for the quickest front half times or optimal acceleration when exiting a turn. We have found that the use of a Synchrometer, allows us to maximize adjustments with the least amount of time. Before getting started, attach return springs and set idle speed. The engine and injector should be at normal operating temperatures.

  1. Injectors with pinch clamps for ram tube retention will need to have the horizontal and vertical cuts in the casting taped from the inside to insure correct reading of the Synchrometer.
  2. Place the Synchrometer on one of the throats and adjust the air flow restrictor so the needle is centered in the gauge. There is no correct starting place for the needle since we are looking for equal airflow not an airflow number.
  3. Verify averages are consistent bank to bank. If they are not, remove throttle linkage and return springs and back off idle stops. Loosen a gold arm for the hex link and, while supplying slight closing pressure to the bank with the higher air flow values, tighten the gold arm for the hex link. This will allow both banks to open the same amount and even the airflow from bank to bank. It may take a couple of attempts before you are satisfied.
  4. Identify butterflies that need to be adjusted to provide equal air flow. Open butterflies and identify which end of the blade points up. Mark the up end with a marker. Butterflies are beveled and need to go back in with the correct orientation (see Butterfly Installation). Also, adjustments to the butterfly are typically done on the end that points up.
  5. Remove the two screws and lock washers that hold the throttle blade, taking care not to drop them into the engine.
  6. Open throttle shaft to wide open throttle while grasping the end of the throttle blade to remove it. Protect the throttle blade from vise damage by using a piece of aluminum on either side. A rod vise works very well also.
  7. Using the throttle shaft witness marks as a guide, insert the butterfly between the aluminum, lining it up with the witness mark. The end of the butterfly to be adjusted should be sticking out of the vise and both throttle shaft witness marks should be hidden.
  8. Lightly tap the blade in the direction required. If the cylinder requires more airr, adjust butterfly as to open it in the throttle bore, and conversely, if the cylinder requires less airr, adjust butterfly to close it in the bore. Remember that .010 of an inch is a lot.
  9. Reinsert butterfly into the throttle shaft. Install and tighten the butterfly screws.
  10. Repeat as necessary. The closer the values, the better your engine will perform.

You have now completed the injector manifold adjustments. Install your ram tubes and enjoy your Hilborn Fuel Injector.

Installation Schematic

Screen Shot 2016-02-09 at 11.30.25 AM

 

Metering Valve Schematic

metering_valve

Manifold Adjustment Video

Synchrometer Tuning Video

Butterfly Installation

butterfly_install

Cam Cover Pump Drive for SB Chevy Engines

Hilborn Part *PDC-4 Cam Cover Drive For Small Block Chevrolet Engines:

1. Loosen oil pan & remove stock timing chain cover, gasket, the three (3) sprocket bolts.
2. Bolt on the hex drive spud using the allen cap screws supplied.
3. Adjust the cover-to-spud clearance by means of the .015” and .030” shim washers supplied. With the timing chain cover gasket off, place the washers on the spud, .015” at a time, until the cover is raised just clear of the engine block. Remove one (1) .015” washer. Install the new cover gasket, which will give proper running clearance. Failure to set the clearance properly can result in damage to the drive and pump!
IMPORTANT! Be sure to remove the HILBORN pump before attempting to remove the harmonic balancer. Failure to do so will result in a broken casting.

Timing Belt Pump Drive for SB Chevy Engines

Hilborn Part *PDC-6 Timing Belt Drive For Small Block Chevrolet Engines:

1. Bore the crank pulley to 1.250” to accept the crank spud.
2. If using a water pump, use a single-groove crank pulley.

Timing Belt Pump Drive for BB Chevy Engines

Hilborn Part *PDC-7 Timing Belt Drive For Big Block Chevrolet Engines:


  1. Pump mounts on the RIGHT side of the engine looking foreward.
  2. A single-groove crank pulley should be used and bored out to 2.250” to accept the crank spud.
Cam Cover Pump Drive for BB Chevy Engines

Hilborn Part *PDC-8 Cam Cover Drive For Big Block 396”-427” Chevrolet Engines:

1. Loosen oil pan & remove stock timing chain cover, gasket, the three (3) sprocket bolts & sprocket. The timing sprocket hub must be reamed to .875” to receive the register on the drive spud. Replace sprocket.

2. Bolt on the hex drive spud using the allen cap screws supplied.

3. Adjust the cover-to-spud clearance by means of the .015” and .030” shim washers supplied. With the timing chain cover gasket off, place the washers on the spud, .015” at a time, until the cover is raised just clear of the engine block. Remove one (1) .015” washer. Install the new cover gasket, which will give proper running clearance. Failure to set the clearance properly can result in damage to the drive and pump!

IMPORTANT! Be sure to remove the HILBORN pump before attempting to remove the harmonic balancer. Failure to do so will result in a broken casting.

VW Turbo Schematic
VW turbo schematic

VW turbo schematic

4-Cylinder Turbo Schematic

4-cylinder turbo schematic

8-Cylinder Turbo Schematic

8-cylinder turbo schematic

How can I plumb a surge tank with mechanical fuel injection?

An electric automotive fuel pump (1) and filter (2) feed fuel from the main tank to the surge tank through a Holley float bowl (3). The surge tank must have a vent (4). Fuel is drawn from the surge tank by the injector pump (5), which delivers the main fuel feed to the barrel valve (8) through a high flow inline fuel filter (6) and shutoff valve (7). The barrel valve distributes fuel to the individual port nozzles (9). To regulate flow, the main jet (10) bleeds off fuel from the pump outlet back to the surge tank. Similarly, the low speed bypass (11) returns some fuel from the barrel valve in the first third of throttle travel. The high speed bypass (12) takes away more fuel from the pump outlet when engine rpm (fuel pressure) is high; usually set to open at 6500 rpm.

surge tank schematic

Hilborn Video Gallery – Check It Out!

We have some awesome videos of customer cars,
dyno testing, drag races, and cool Hilborn stuff.
Checkout our videos.

Experience IR…

Individual Runner, Incredible Ride!