Frequently Asked Questions

Posted by Chris Myer 06/1/15 3 Comment(s) General Studies and Buyer's Guides,

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Kit and System Selection


What's the difference between a 4-bbl Multi-Point and a Stealth Ram system? - Both the Holley 4-bbl Multi-Point Fuel Injection Kits and the Stealth Ram Fuel Injection Kits include an intake manifold that is pre-drilled for individual fuel injectors for each intake port. From that perspective, they are both multi-point fuel injection kits. But the kit that is labled as a 4-bbl Multi-Point kit utilizes a 4-barrel throttle body that bolts in place where the carburetor is normally situated. This throttle body does not have injectors to provide fuel, but in just about every other way resembles a carburetor, even utilizing a carburetor-style air filter.

The kits labled Stealth Ram utilize a common plenum on top of the intake and are fitted with a more traditional (from a fuel injection perspective single-door throttle body, facing forward (hence the "Ram" part of the name.) These have flange to which a coupling and piping is used to attach the air filter, which is typically mounted in the path of cooler outside air.

Do I need a Holley Touchscreen? Is this the same as the Handheld Controller? - The Holley Touchscreen is not needed to operate any of the different Holley Fuel Injection Kits or Fuel Injection Systems. That said, we've found that nearly everyone who sees one in operation immediately wants to buy one! While the Holley Touchscreen can do everything that the Avenger Handheld Controller can do, the Handheld Controller serves a very specific purpose. It is intended to offer fast system setup and straight-forward monitoring of system parameters to users who do not want to have to get involved with computers and software to set up their systems. The Touchscreen lets you adjust virtually every setting and monitor all system parameters on a bright, clear, graphics display without the need to have a laptop in your vehicle.

I'm running dual carburetors. Can I use Holley TPI fuel injection? - Absolutely! Select the Holley Fuel Injection 2-BBL TBI Kit or any of the Holley Fuel Injection 4-BBL TBI Kits. Then, add the optional Holley 558-206 Dual TBI Harness and substitute it for the single TBI harness found in the kit. It is noteworthy that, if you use an Avenger kit (without the laptop) you will have to need to download the Holley HP/Dominator Tuning Software, acquire a USB cable, and modify the single-TBI setup pre-configured for your Holley Avenger kit. Sound difficult? Find a good Holley EFI Installation Technician to do the job for you.

What does Holley mean by "Plug And Play"? -






How do I setup the Holley Avenger? - The Holley Avenger Fuel Injection Kits were designed to allow someone with absolutely no knowledge of fuel injection or computers to install a fuel injection system on their car and get it completely operational simply by asking some simple questions. We have a great step-by-step video of the Holley Avenger setup process, but we thought we'd detail it here to so that you can quickly see how easy it really is.



  • 1. Install the Holley Avenger Fuel Injection Kit according to the included instructions.
  • 2. Turn the ignition power on.
  • 3. Select "Start Wizard" on the Avenger Handheld.
  • 4. Do you want to create a new Calibration? Select "Yes."
  • 5. Select the injection type. (This is simply the part number of your Avenger Fuel Injection Kit.
  • 6 Select Engine Size.
  • 7. Select the Cam Type.
  • 8. Will the ECU control timing for this application? Select "Yes" or "No"
  • 9. Select the RPM Signal source.
  • 10. Select "Yes" to load the calibration that was just created into the Avenger ECU.
  • 11. Shut the ignition power off.
  • 12. Select "Start Wizard" and this time select "TPS Autoset" and then "Start".
  • 13. Press the pedal to the floor twice and select "Done."
  • 14. Start the car.

Seriously, that's it. More detailed instructions are provided in the installation manual, or visit the video above.




Fuel System (Pumps, Injectors, etc)


How do I calculate fuel pump size? - Fuel pumps are typically rated in either liters per hour or gallons per hour. The amount of fuel required by an engine is based on something called the Brake Specific Fuel Consumption, but you don't really need to know that. Suffice it to say that a naturally aspirated engine needs less fuel than a turbocharged, supercharged, or nitrous-injected engine (assuming you're using a dry nitrous system.) Also, keep in mind that there is generally no problem if you run a larger fuel pump than you require. Fuel injection fuel pumps simply return the unnecessary fuel to the fuel tank, so this is only a problem if your return line isn't large enough to handle the return fuel. Use these calculations:


  • Naturally Aspirated Engines: Maximum Projected Horsepower * .38 (liters per hour)
  • Turbo/Supercharged or Dry Nitrous Engines: Maximum Projected Horsepower * .47


Again, since too much fuel isn't a problem, if you round up a bit you're always okay. If you prefer gallons per hour, take the number you just calculated and divide it by 3.785.

How do I calculate fuel injector size? - Like fuel pumps, having a little bit too big of a fuel injector generally isn't a problem, but don't get ridiculous. We make things easy by simply using the fuel pump size calculated above (in liters per hour) and dividing that by 16.67 to get the injector size in cc's per minute. Holley EFI keeps everything easy by putting everything in lbs per minute, so you can also come up with that by dividing cc's per minute by 10.5.

Will any injector work with my Holley EFI Fuel Injection System? - Keep in mind that, when selecting fuel injectors, there are two considerations: fitment and drive. The Holley EFI ECU's (Avenger, HP, and Dominator) are all able to drive almost any common fuel injector, whether high or low impedance. If you have any doubt about the particular injector you have, don't hesitate to contact us. Injector fitment is another issue. There are usually 4 issues to consider.


  • Injector Inlet Size and Shape
  • Injector Outlet Size and Shape
  • Injector Length
  • Feed Type


If you are purchasing one of the Holley Avenger Fuel Injection Kits, all of your thinking is done for you. These kits include the proper fuel pump and fuel injectors for the precise application for which it was designed. If you are purchasing one of the Holley HP Fuel Injection Kits, you will need to source your own injectors. All of the HP kits that include the manifold use what is known as a Bosch EV1-style injector. Holley also offers EV1-style injectors separately from their kits. You can find these in the EFI Accessories/Fuel Injectors category. You can purchase the Holley injectors with complete confidence, or you can source any other injector as long as they are EV1 style.

EV1 injectors do not fit in every application, however. GM LS engines, for example, use what is called EV6-style injectors. EV1 injectors can be used in LS engines with the use of an O-Ring adapter specially sized for that purpose. These are also available in the Fuel Injectors category.

Some applications require completely different injectors. Many Japanese engines use side-feed injectors. There is no way that you can easily fit a top-feed injector into an application built for a side-feed. In the event this is your situation, you have a few choices. You can look for a higher-flow side-feed injector for your application. These are often available for more popular vehicles, although the cost is generally quite high. You can look for a top-feed conversion kit. These are not inexpensive, but generally you will save in injector cost whatever the conversion kit will cost. As a worst case you may have to have a top-feed fuel rail made for your application.





Ignition and System Timing


What about ignition timing? -




Other Great Questions


How does the Nitrous Oxide Control Work? -

How does the Water-Methanol Control Work? -

How does the Boost Control Work? -

Holley EFI offers tuning based on Speed-Density, Alpha-N, and Combo. What's all that? - One of the most foundational concepts of fuel injection programming is the fuel map. Engineers call this "Load Sensing" and it is the method that the Holley EFI ECU uses to determine how much fuel to spray into the engine. Holley's tuning software offers Speed-Density, Alpha-N, and a combination of these two load sensing methods.

It is important to have a basic idea of what these methods are and when each is appropriate. Speed-Density allows the tuner to create a 2-dimensional map of engine speed (RPM) versus manifold air pressure (MAP). This is what most novices are familiar with. The tuner adjusts the amount of fuel (in pounds per hour) that is delivered to the cylinder based on these two dimensions. This method is generally the right answer for most applications, and is really mandatory in turbo or supercharger boosted applications. Only the Speed-Density method can account for various amounts of manifold air pressures which are experienced.

Alpha-N load sensing allows the tuner to create a 2-D map of RPM (or "N") versus throttle angle (Alpha), as sensed by the throttle position sensor. Alpha-N has a very specific benefit in that it allows naturally-aspirated engines that develop very little vacuum (due to extrodinary cam durations) to be able to idle. Alpha-N is also commonly utilized in individual-runner applications where there is no shared manifold from which to measure a steady MAP, although this can sometimes be overcome by building a small shared-vacuum manifold with vacuum hoses, specifically for estimating the MAP across the intake runners.

Combination load sensing provides the benefits of both methods. When Combo load sensing is selected, an Alpha-N idle fuel map is added, where fueling based on throttle position can be tuned up to a certain RPM. Beyond that RPM, the normal Speed-Density map is used. This allows the most radical boosted engines to idle much more naturally without any of the limitations of Alpha-N fueling at higher RPMs.

Join the discussion below or click here to read Chris's other articles on fuel injection!

3 Comment(s)

George Jennings:
11/15/16, 03:29:25 PM

I am thinking of going with your Holly sniper fuel injection system but I plan on running either a pro charger or a TwinTurbo set up can I still use the feeling Jackson system will I have to change to something else

Chris Myer:
11/15/16, 05:33:21 PM

At this time Holley the Sniper TBI system that is available is not able to work with boosted applications. But Holley has big plans for this product line and I expect that a boost-capable Sniper may be in the works--but no ETA is suggested.

If you don't have definite plans to boost your engine just yet, I would recommend going with the Sniper. First, you get the benefit of EFI now without waiting. Second, you will have your fuel system upgraded to support EFI, making your next upgrade that much easier. And you can either use the Sniper in another project or sell it to a buddy to recoup some of the cost.

After you boost your engine, there are a broad range of options. If you want to stick with a TBI system, the Terminator EFI system could work (though it would have to be custom tuned instead of using the Setup Wizard.) On the other hand, you may decide to go with an EFI manifold and then one of the Holley HP ECU-Harness Kits would be a great choice. A few links are below for your consideration now, but be sure to stay in touch as you progress and I'll be glad to give you more specific suggestions.


Terminator EFI

HP ECU & Harness Kits

Jim Menke:
04/29/20, 01:21:30 PM

Thinking about putting a Quadrajet Sniper EF I on a Restored 1970 GTO with a 455/400....It's a 10.25 to 1 motor.... the car has 3.08 gears and it gets 9 to 10 MPG....With 93 octane and Lucas Octane boost additive, it still rattles a little when I get it...I bought a D.U.I custom curved Ignition for it and it helped...a little........Question 1. will the Sniper EFI cure the detonation issue or help maybe?........Question 2. Will the Sniper EFI give me a little better fuel milage?Thanks Jim

Chris Myer:
06/3/20, 05:32:37 PM

I would not expect a big change in the detonation simply as a result of the switch from carb to EFI, although an improved tune could have an impact. Likewise, EFI by itself is not a guaranteed improvement in fuel economy but if you have your system professionally tuned (not simply using the self learning) then you can just about count on seeing a significant improvement. The Sniper self-tuning capability is quite impressive but there is no question that professional tuning produces results. See options here.

Corwin Bachran:
07/14/21, 10:53:06 AM,

I have a Sniper setup on my '67 mustang with a built 347, and adore it... At least after moving to a torquer II intake to remove the dual plane divider issue.I just got a 2bbl sniper for my '85 Landcruiser. I'm concerned the adapter from Sniper to Toyota isn't an open chamber, it's 2 holes, one under each barrel. Does the 2bbl Sniper have the same MAP sensor/idle issue as the 4bbl? It'll be easy enough to machine out the adapter from 2 holes to a large oval, but I would rather not if I don't have to.

Chris Myer:
08/20/21, 11:27:16 AM

I'm not familiar with a specific MAP Sensor / Idle Issue on the 4BBL Sniper, at least not as it relates specifically to any hardware issue. If you flip the unit over you'll see the channels that are machined for vacuum to get to the internal MAP sensor. As long as those are there and not blocked I'd think it would be fine.I did have one customer who was getting no response on the MAP sensor--ever. I asked him to send me a picture of the bottom of the unit. Holley manufacturing had failed to machine the paths for the MAP sensor to read vacuum. Oops! Of course Holley took great care of him and I never saw another that missed that step.

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