Holley Super Sniper EFI Install – The Basics

All images courtesy Holley unless otherwise noted. Are you converting an older car into a super strip burner and like the old school look of a big four barrel carb sitting under the hood, but want the performance benefits of fuel injection? EFI systems that look like an old school Holley 4150 carb tend to top out their horsepower support at about 700 galloping ponies, but what if you’re boosting it and shooting for, say, around 1,200 horses? What then? Holley has just introduced an update to their Sniper EFI System. They call it the Super Sniper EFI and claim it will support up to 1,250 HP with forced induction and 700 normally aspirated.

Holley Super Sniper EFI Install - The Basics

All images courtesy Holley unless otherwise noted.

Are you converting an older car into a super strip burner and like the old school look of a big four barrel carb sitting under the hood, but want the performance benefits of fuel injection? EFI systems that look like an old school Holley 4150 carb tend to top out their horsepower support at about 700 galloping ponies, but what if you’re boosting it and shooting for, say, around 1,200 horses? What then? Holley has just introduced an update to their Sniper EFI System. They call it the Super Sniper EFI and claim it will support up to 1,250 HP with forced induction and 700 normally aspirated.

Introducing the Holley High-Horsepower Super Sniper 4150 EFI

Holley came out with the Sniper EFI 4150 not long ago, and it made quite a splash. However, it continued to just miss the mark with serious racers because it was limited in the amount of horsepower it could support. This has been rectified in the newest iteration of the line. There are two versions, collectively “Sniper EFI’s High-Horsepower Super Sniper 4150.”

Strong and Stronger

The first of these will support forced induction engines producing up to 1,250 HP and up to 700 in naturally aspirated engines. This unit is equipped with eight injectors that flow up to 100 pounds of fuel per hour. The baby brother will support up to 650 horses and has four 100 pound injectors. Basic installation for both is four wires - Batt+, Batt-, RPM and switched ignition, preferably dedicated.

A single-stage progressive nitrous controller is also built into both versions, eliminating the added expense of an external nitrous controller, leaving you more money for speed upgrades. There’s also an eight-pin harness that gives more sensor functionality and programmable outputs and inputs than earlier standard Sniper EFI systems. They’re also compatible with both wet and dry nitrous systems.


These are direct replacement conversions for the majority four barrel carb intakes with no manifold swap required. Holly says “the high-horsepower Super Sniper 4150 is equally suitable for draw-through (Roots-style blowers) and blow-through (Paxton blowers and turbochargers) forced-induction engines.” There’s an easy to use handheld controller that Holley says is user-friendly and controls all operations of the EFI including boost. It’s fully programmable for the air/fuel curve you want. There’s also an Advanced boost control “module” that can be downloaded to give you boost vs time and boost vs RPM.

Assemble Your Tools

Don’t be cheap with the stripper/crimper you use.

You really won’t need many other tools beyond the flat screwdriver, half inch socket or wrench, and something for the fuel line that’s needed for working on a carburetor for this conversion/installation. These are:
• #2 Phillips screwdriver
• Wrench set
• Wire stripper/crimper
• Allen wrench set
• 7/8 inch stepper bit or 3/4 inch drill bit
• Drill and bit set
• Digital multimeter

NOTE: Before Starting This Upgrade

Disconnect the battery. Charge the battery if not fully charged.

The Right Pump

Your car’s fuel and exhaust systems have to support the new EFI being installed. Chances are, if you’re upgrading from a carburetor, you’re going to need to at least upgrade your fuel pump to an electric one that will supply a constant 60 PSI no matter what load you’re putting it under. The new pump should be installed in the fuel tank to help cool it, or if that can’t be done, no more than three feet from it. There should also be pre- and post-filters installed before and after the pump.

Stay Up to Date

It’s highly recommended that you update your fuel system prior to performing this installation. Old fuel line won’t handle the pressures that EFI needs.

Check the fuel system thoroughly. Any cracked rubber hosing should be replaced, as well as any hard line showing rust. I would recommend running half inch hard line along the frame and then using 3/8 inch return and ½ inch supply hoses with 6- and 8-AN fittings from Earl's, or something similar.

You also need to make sure you’ve got an O2 sensor bung in the exhaust somewhere about three to five inches after one bank’s cylinders come together, before any catalytic converter(s) and at least ten inches before the exhaust outlet. The kit comes with a bung you clamp onto the exhaust, but one that’s properly welded is much better. Also, it must be installed so that the sensor is no less than 10 degrees above the horizontal to protect it from damage from condensation in the pipe.

Remove the Old Carburetor or EFI Unit

Image by Mike Aguilar

If you’re building a crate engine, you can skip this step unless it has a carb or EFI installed already. Label and remove the throttle and kickdown (if equipped) cables along with their mounting stubs on the linkage. Next, label and remove all vacuum lines. If you’re replacing a carburetor with an electric choke, tape off the connector for it and secure it to the wiring loom somewhere out of the way.

Disconnect the fuel hardline from the tank at the fuel pump. This requires either a1/2 inch or 9/16 inch line wrench. I would remove the fuel pump and slap a block-off plate over the opening because a mechanical fuel pump robs a couple HP at higher RPM, but you can just bypass it if you want.

Remove the Carb

Disconnect the fuel supply at the carburetor/EFI. Have a rag handy to catch any spillage. Using a ½-inch wrench or socket, remove the four carburetor hold-down bolts , making note of the linkage bracket locations, if they are secured to the base. Make sure the mating surface is perfectly clean.

Mounting the Super Sniper On Top of a Blower?

This step is only for those installing their Super Sniper EFI on top of a draw-through or Roots-style blower. If you’ll be using a Paxton blower/supercharger or a turbo, skip ahead to the next step. There’s a 1/16 inch NPT plug in the front side of the Super Sniper EFI that needs to be removed and replaced with the barbed nipple that’s included with the kit.

Deal With the Set Screws

Next, thread the 10-32 set screw - also included - into the machined hole in the bottom of the unit. You should use a small pointed punch to secure this set screw by peening it in three places around its circumference.

Mount the Super Sniper EFI Unit

Make sure the mounting studs are long enough and change as needed. I use a stud puller to remove them, but you can counter-lock two nuts against each other and turn the bottom one to remove them. Slide the new gasket over the studs, followed by the Super Sniper EFI unit.

Torque it Down

Run the ½-inch nuts down by hand, remembering to replace any brackets that came off when the carburetor was removed. Torque these down to about 30-40 inch-pounds. Connect the throttle/kickdown linkage in the locations indicated above. Check the pedal for full and unimpeded motion.

Make Fuel and Vacuum Connections

Attach the return line to the return port on the EFI unit. Pick one of the three inlet ports and attach the fuel supply line, installing plugs in the unused inlets as needed. If you’re installing it atop a blower, connect a vacuum line from the 1/16 inch barbed inlet to the corresponding port on the intake manifold below the blower. If equipped, connect the vacuum advance (3/16 inch ported vacuum) and power brake hoses. Be sure to plug any unused ports or hoses.

Important Note!

On boosted applications, an external pressure regulator must be used, and the onboard regulator and the input port on the same side must be plugged. The two ports on the front of the EFI body must be used for supply and outlet to the regulator. Which side you choose for inlet and outlet is up to you.

Route Wiring and Make Connections

Route the black and red wires to the battery, avoiding any pinch points and the exhaust. Use electrical tape, wire looms or wire ties to make a cleaner installation. Install blue or yellow #10 ring terminals on them and set them aside for now. If the battery terminals on the wires are OEM or molded, I would replace them with a set of quick-connect terminals that allow for the easy connection of accessories and for easy disconnection and reconnection of the battery when working on the car.

Match the Wires

Locate the connector harness that has the green and purple wires twisted together and a lone yellow wire. Connect this yellow wire to the coil negative either by splicing into the HEI connector or using a blue #10 ring terminal at the coil negative. Now locate the two-wire connector with the white and brown wires, connecting the brown wire to the tach lead. If you route this directly to the tach, make sure the wire goes through a hole with a grommet.

Connect the Power Source

The red and white (or pink) wire needs to be connected to a relatively clean switched power source that has power both when running and when starting. As the main switched power for the unit, I would tap into an appropriate wire off the ignition switch under the dash and run it to a relay under the hood, again through a grommet, and connect the red and white wire to the relay’s output. The relay can get power through a fused 12-gauge wire run directly to the battery. It can also be grounded directly to the battery.


If you’re using a CD box, such as an MSD 6AL, connect the purple ignition adapter wire from it to the purple wire in the two-wire harness. The yellow wire isn’t used. However, the brown wire still goes to the tach lead.

Relay Wiring

Diagram by Mike Aguilar

If you’ve had to install a new electric fuel pump, you’re going to need to run wiring to it. Run power from the pump to a new relay, making sure to use a fuse right after the relay. The pump can be grounded to the chassis. The blue wire in the seven-pin connector (with the ignition, power, and ground wires) will go to the switch input on the relay (relay pin 87 in image above).

Connect the Touchscreen Controller

The touchscreen controller can be connected for initial startup ad tuning only, or it can be mounted in the car for easy access. If you choose to mount it inside, you need to route the controller wiring harness through an opening in the firewall/bulkhead with a grommet. Make sure there are no obstructions that can be drilled into on either side before drilling. Sliding the grommet over the connector before putting the grommet into the firewall opening will let you drill a small hole for this.

Install the Sensors

The Holley Super Sniper High Performance EFI kit comes with a coolant temperature sensor and an O2 sensor, both of which must be used for the EFI to work properly. The temperature sensor needs to be installed anywhere but in the thermostat housing, in the intake, head or block. The radiator can be used as a last resort.

Somewhat strangely, the kit only comes with one O2 sensor instead of two. It only needs to be installed to monitor one bank, but as mentioned, it must be about two to three inches past where the individual pipes collect, before any catalytic converter, and at least ten inches before the outlet. If you’re installing aftermarket headers and you mentioned they’d be going on an EFI engine, at least one already has an O2 sensor bung welded in. Install the sensor there, preferably using anti-seize compound, and plug the other one if needed.

The O2 Sensor

If you don’t have an O2 bung ready for you, you can mark and drill a 3/4 inch hole in one of the exhaust pipes in the aforementioned location and use the bung clamp supplied. Deburr the hole before placing the gasket and the casting on the pipe. Put anti-seize on the clamp bolts and securely tighten the clamps around the exhaust pipe. Securely install the Oxygen sensor and route the wires to keep away from the exhaust and pinch points to connect the O2 sensor connector from the EFI.

Initial Calibration in Basic Configuration

This completes the basic installation of the Holley Sniper EFI 4150 Super Sniper 1250/650 kit. Nothing else is needed unless you want to study up and tap the advanced potentials of the unit (ie fan controls, nitrous solenoids, AC kill, etc.) Connect the battery and make sure the connections are clean and secure. ¬Turn the key to the run positon without starting it and run the Wizard (bottom right) on the controller as follows:
• Select the proper Sniper EFI system and press Next.
• Select the correct number of cylinders and press Next.
• Choose your engine size using the slider bar and press Next.
• Slide the bar to your desired HOT (once the coolant reaches 160°) idle speed and press Next.
• Choose the type (stock or mild, street/mild strip, race) and press Next.
• Select the type of ignition system you’ve got and press Next.
• Select what type of power adder, if any, you’ve got (nitrous, turbo, supercharger/blower, none) and press Next.
• Move the slider to choose the air-fuel ratio (AFR) at wide open throttle without boost and press Next. Skip if un-boosted.
• Set the desired AFR Offset for each seven pounds of boost and press Next. Skip if naturally-aspirated.
• Press Start to send the calibration file to the ECU on the EFI unit.

Verify All Sensors Are Working Properly Prior to Initial Startup

Turn the key off and back on to reboot the system. Once the touchscreen boots, you should hear the fuel pump pre-pressurize for five seconds and turn off. Check for fuel leaks and correct as needed. Bring up the Monitor function from the Home screen and then select the Monitors screen. Select the Initial Startup icon from the screen that opens. You should see six sensors:
• Engine RPM-Should show “Stall” with engine off.
• TPS-Throttle Position Sensor-Should read zero with engine off. Watch it move as you slowly depress the throttle pedal. If not reading at least 85% at WOT, check linkage for binding.
• MAP-Manifold air pressure. At normal elevations this should read around 95-102. Numbers as low as 75 could be normal for higher elevations.
• CTS-Coolant Temperature Sensor
• IAC- Position Two to ten percent is normal when hot once calibrated.
• Battery-This will read actually battery voltage and should be at least 12 volts.
Any issues with these initial readings need to fixed before moving forward.

And now... Crank that puppy up!

Crank the engine while watching the controller. You see the display switch to “Syncing” until showing the RPM signal. The engine should fire and come to an idle. If not, you’ll need to figure out why using the basics and Super Sniper online troubleshooting guide. If the engine can’t get to a decent idle, adjust the idle speed screw accordingly. Let the engine warm up as you check for oil, coolant and fuel leaks front to rear.

After Startup/Warmup Health Check

Once the engine is running at the correct RPM and has reached the operating temperature range, you need to use the handheld controller to make sure everything’s hunky-dory. Select “Multi Gauge” from the “Monitor screen. Select the “Air/Fuel Ratio” icon next. You’ll see the following:
• AFR,AF-This is the actual AFR that the O2 sensor is reading. It should be close to the next reading, the target AFR.
• Target Air/Fuel Ratio-This is selected by the ECU based upon a number of operating variables and will vary.
• Coolant Enr. %- This is how much “choke” or enrichment the EDU is adding and is opposite what one would think: 100% means zero artificial enrichment is being added.
• CL Status-This tells you if the system is running in “Open” or “Closed” loop. Open loop is basically “Limp Home Mode” where no control over the AFR is being maintained, the engine is simply maintained running until the key is turned off. Closed Loop is indicated by CloseLp.
• CL Comp, % -This shows how much the computer is varying fuel flow during Closed Loop operation. In Open Loop this will read “0.”
• Learn Status-If “Self-Tuning” is enabled (it is by default) this should read “Learng” once the system enters Closed Loop operation. Until then it will read “NoLearn.”
• Current Learn, %-This doesn’t show how much learning the ECU has done, but also shows how much the ECU is controlling the flow of fuel as compared to the base fuel map. You might see between -20% and 20%. Negative numbers indicate the Super Sniper is reducing the amount of fuel as compared to the base map.
• Inj. PW, msec-This number will vary wildly as you drive and indicates the amount of time the injector is open in milliseconds.
• RPM, rpm-Engine RPM. Check this against your tach.
• Fuel Flo, lb/hr-This will also vary wildly as you drive (but may also stabilize if you maintain a constant speed) and shows the instantaneous amount of fuel is going into the engine as you drive. The reading is in pounds per hour.

Note: Make sure all of the above readings are within operating parameters before heading off on your initial test/learning drive.
Note: ECU won’t go into “Learn Mode” until “Coolant Enr. %” reaches 100% or zero enrichment.

Idle Calibration

Now you need to set the idle and throttle plate. Go back to the Initial Startup gauge screen and look at the IAC Position. If it reads between two and ten percent, all’s good. If not, make sure the parking break is set, then put the transmission in neutral and adjust the idle screw until the IAC Position is corrected. Make sure the TPS value doesn’t change as you do this. If it does change, shut the engine off, restart it and get back to this stage. Repeat this until the desired reading is achieved.

First Drive

Once the “in the garage or driveway” stuff is done, head out for a leisurely drive to finish the learning process.

By now your new Holley Super Sniper High Performance EFI has almost finished the learning process at idle. Now it’s time for you to teach it how to work while you’re driving. Holley recommends that you have someone drive for you while you monitor the health of your engine and the tune. The self-learn process needs you to drive around.

However, you need to drive around city streets for a bit, while someone monitors the controller and how far along in the learning process it is by keeping an eye on the “CL Comp” value mentioned above. Once it reaches zero, move on to the next step.

You’ll start by letting it idle for a few minutes, then slowly accelerate down the street and come to a stop, doing this a few times. Then turn on the air conditioner for a bit. Next, hit the freeway and just drive with the flow. Once that’s been learned, it’s time for what we came here for: Wide Open Throttle runs! Don’t get in trouble though.

Race It!

Once all the basic self-learning is done, take it to the track and see how much improvement you got.

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About Mike Aguilar 235 Articles
Mike's love of cars began in the early 1970's when his father started taking him to his Chevron service station. He's done pretty much everything in the automotive aftermarket from gas station island attendant, parts counter, mechanic, and new and used sales. Mike also has experience in the amateur ranks of many of racing's sanctioning bodies.
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