EFI Swapping A Dragster With A Holley Sniper Stealth 4500: Part 1

Electronic fuel injection (EFI) in drag racing was considered a black art for the longest time — it was mysterious and difficult for those accustomed to carburetors and mechanical fuel injection. As technology has progressed, EFI has permeated every corner of drag racing, but for many grassroots racers, it’s still oft considered too complex. We decided to see how easy an EFI swap could be on a big-block-powered dragster built for bracket racing, using a Holley Sniper Stealth 4500 EFI system.

Carburetors have been a staple in drag racing since the beginning of the sport and most racers are accustomed to making them work. The electronic jets that EFI brings to the table scares many racers, however, the upside to the technology is huge even in a bracket racing application. So why not take your typical big-block Chevy dragster and convert it to EFI to see if there really is a benefit?

Holley’s Sniper series of EFI systems were designed to make EFI swaps simple on older engines, with its many features like simple wiring, an ECU that’s a part of the throttle body, and self-learning abilities. There are several different systems available from Holley based on an engine’s size and horsepower output that make it easy to get the right one for your application. The Sniper EFI Stealth 4500 is designed for engines that make at 800-1,500 naturally-aspirated horsepower, or up to 1,250 horsepower with forced induction. The throttle body is a direct fit replacement for Dominator-style 4500 flange carburetors on the Sniper 4500.

The Who And Why Behind The EFI Swap

Your standard bracket racing vehicle isn’t as complex as a high-end heads-up race car; its set up to run a specific elapsed time repeatedly with deadly accuracy. For this project, we’re using a 225-inch hardtail dragster that was originally built by Horton Race Cars. Powering the dragster is a 509 cubic-inch big-block Chevy that’s topped off with a set of Brodix cylinder heads and a Wieand intake. Before the swap, fuel and air was mixed by a 4500 Dominator carburetor that had been worked over by Davinci Carburetors.

The best pass the owner had made was an 8.49 in bracket racing trim and the car would run within a few hundredths depending on the weather. Those are some respectable numbers, but the car did have consistency and tuning issues with the carburetor at times, so that made it an ideal candidate for this EFI swap. This project is as real as it gets: no big shop, dedicated mechanics, or trained tuners doing the work…just two racers in their home garage.

EFI provides precise fuel delivery, and the Holley Sniper can do that through its self-learning ability. With EFI, you are also using a laptop to do your tuning rather than physically changing the metering blocks, air bleeds, jets, power  valves, and squirters on a carburetor. – Matthew Lunsford, Holley

Introducing EFI into the picture for a bracket car can be a catalyst for improved consistency. A carburetor can only be tuned for one specific set of conditions, and we all know that weather is a very dynamic thing. EFI has the ability to adjust the fuel and spark the motor receives on the fly, thus eliminating some of the consistency issues you might have at the track.

Matthew Lunsford from Holley is part of the team that developed the Sniper EFI system — he explains why the Sniper is a great fit for a bracket racing application.

“EFI provides precise fuel delivery, and the Holley Sniper can do that through its self-learning ability. With EFI, you’re also using a laptop to do your tuning rather than physically changing the metering blocks, air bleeds, jets, power valves, and squirters on a carburetor. There’s also the added safety features EFI offers; for example, if your engine starts to go lean, the ECU will automatically add fuel to keep your target AFR (air/fuel ratio). There’s also built-in data logging with the Sniper system, so you can see exactly how your engine is performing.”

How To Feed The EFI Beast

If you’re contemplating an EFI swap, the first thing you need to address is the fuel system. The fueling needs of a carburetor versus that of an EFI system are very different in terms of design and parts. Roughly the same volume is needed with both types of fuel delivery, since the same old equation applies (fuel + air + spark = horsepower). However, EFI requires significantly higher fuel pressure than a carburetor, so you’ll need to change the fuel pump to something that can continually produce the minimum 58psi of fuel pressure required by the Sniper system. You’ll also need to add are pre- and post-pump fuel filters to the fuel system; we will cover that more in a minute.

The Holley Dominator billet fuel pump is the perfect choice for a project like this. The pump flows more than enough fuel and has a footprint that allows it to be mounted easily in tight spaces.

For the dragster’s fuel system we consulted with the experts at Holley to see what parts we would need to keep the Sniper flush with fuel. They recommended for the backbone of our fuel system we use a Holley Dominator in-line billet fuel pump (P/N 12-1600). This fuel pump can flow upwards of 160 gallons-per-minute and will support up to 1,600 horsepower in an EFI setting.

Matthew outlines why going with this Dominator pump is a great choice for any EFI swap project like what we’re doing with the dragster.

“The Dominator pump is a versatile pump that works well in different applications. For drag racing, its billet construction helps create great longevity. The pump has -10 ORB fittings on the inlet and outlet sides for pumping ease. The Dual pump design allows you to use the EFI trigger when higher fuel flow is required,” Matthew explains.

Fuel pressure is critical for an EFI system, so having a regulator that is accurate is a must-have item.

If you plan on running a power-adder with the Sniper system, you also need to take that into account while designing the fuel system. Matthew points out that the fuel pump needs to have the ability to flow the proper amount of fuel for the amount of power you want to make. We used a Holley billet EFI bypass fuel pressure regulator (P/N 12-848) because it’s a versatile fuel pressure regulator that will work in our NA application, or in a boosted application if we go down that road in the future. When plumbing the fuel system it’s important to make sure the fuel return line you plumb into the system is large enough, because if you go too small you could experience erratic fuel pressure in an EFI application.

Another thing that’s different with an EFI system fuel system versus a carbureted fuel system is the use of fuel filters. When you’re acquiring parts for your swap, you must ensure you get the right filters to prevent damage to the fuel injectors. For our fuel system, we used a Holley 100 micron pre-filter (P/N 162-577) and a 10-micron post filter (P/N 162-575).

The Holley Dominator fuel pump and fuel filters can be configured in many different ways based on your application. With the dragster, we had to get creative on how we mounted everything while making sure it could all be accessed for maintenance if needed.

“Fuel filters are imperative to EFI because of the size of the orifices in the injectors. Most injectors have a little basket filter as the last defense, and that’s just a safety net to save the injector from damage. Injectors are expensive to replace, and filters keep larger pieces of debris from going through the pump and then the smaller pieces are filtered after the pump before fuel makes it to the injectors,” Matthew explains.

Installation Of The Sniper System

One of the best things about how the Sniper system addresses an EFI conversion is how simple it really is to install. Most racers are intimidated by the idea of fuel injection because of what they think it takes to make it work — the Sniper system eliminates all of those fears.

The throttle body and ECU are combined into one unit with the Sniper 4500. It literally fell into place when it came time to test-fit it to the intake, without any issues at all. Routing the wiring wasn't that bad either, and you have a lot of freedom to do it different ways based on your application.

Holley approached the design process of the Sniper 4500 from the very start to make it easy to install.

“The Sniper 4500 is designed to be a direct bolt-on replacement for most 4500 carburetors. We included scoop mounts on top of the throttle body and all of the dimensions of the unit are similar to a 4500 carburetor to make swapping simple. The ECU is actually on the throttle body itself, so that removes the need to have an ECU mounted somewhere else, and removes complex wiring. When you look at the wiring harness that is used you can see they are simple and use OEM quality connectors,” Matthew says.

You may have heard before that a product is “simple” to install but find out it’s far from easy when it comes time to do the installation yourself.

The Sniper 4500 is designed to be a direct bolt-on replacement for most 4500 carburetors. – Matthew Lunsford, Holley

The process was very straightforward and the directions are clear and concise, with plenty of diagrams that show you what needs to be connected and what all of the wires are for. We only had to use the basic four wire hook up for our installation that included the switched 12-volt ignition, battery ground, battery positive, and the RPM signal; the rest were removed from the harnesses to help with routing. The directions outline which color the wires are, plus the wires themselves also have their application information printed on them. All we had to do was run the wires from the harness to the correct locations on the car. For the switched ignition, we used a switch on the dash to power up the Sniper separately from the main power so it could remain powered up, even when the car wasn’t running. The battery power and ground were run directly to the battery per the directions; this is very important to do and shouldn’t be deviated from. Finally, we spliced into the RPM signal right at the MSD box to complete the wiring.

After that was done, we just cleaned up where the wires were, ran the setup wizard per the directions, and the dragster started up on the first attempt.

Wiring up the Sniper to the dragster was very simple and the directions did a great job explaining which wires you need to use. The handheld display comes with a long cable and the menus are easy to navigate.

The Sniper can be as complex as you need it to be. The wiring harness has provisions for many other inputs and outputs based on your application. You can turn on a water pump, run a nitrous system, have a boost controller, and much more all function through the Sniper if you so choose.

“The Sniper has a simple calibration wizard that builds a calibration for the specific engine by asking a few simple questions, such as how many cubic-inches the engine has, what type of camshaft, and what type of ignition system is being used. It receives feedback from the sensors that allow the system to self-learn and adapts to the engine that it’s been installed on and will constantly optimize the tune if left in Holley’s self-learning mode,” Matthew explains.

The calibration wizard comes up when you power up the system the first time as an option on the touchscreen. When you’ve finished the calibration wizard portion of the initial setup, the touchscreen is still an important part of the Sniper system. You can use the touchscreen to make adjustments to different parameters in the ECU and activate other functions of the Sniper system. The touchscreen can also be used as a digital dash to monitor all of the important engine vitals like RPM, AFR, throttle position, injector duty cycle, and more.

How Does This Thing Work?

The Sniper system controls your engine’s functions just like any other EFI system: it makes sure the right amount of air, fuel, and spark are all mixing inside the cylinders to keep the engine happy while making power. With the Sniper system, you don’t have to worry about doing a massive ignition upgrade, since it will work with a distributor and ignition box. If you would like the Sniper system to have full timing control you can use a Holley HyperSpark distributor. We will cover more about how the ignition works with the Sniper system in part two of our EFI swap series.

After you run the setup wizard and you’re able to get the engine started, the self-learn mode kicks in to start optimizing the tune-up in the EFI system. Matthew gives a basic overview of how all of this works when the Sniper system is used.

“The oxygen sensor in the exhaust reads the AFR, and the closed-loop fueling strategy can add or subtract fuel to meet the target AFR that’s programmed by the user. Once the learning starts happening, it uses the values of closed-loop (how much fuel is being added or subtracted) to populate a learn table. As closed-loop approaches 0-percent correction, learning is done in that area. When a user goes down the track with a new combo or new parts on an existing combo, the fueling tune will optimize itself as passes are made until the closed-loop is no longer doing any correction,” Matthew says.

The included O2 sensor needs to be mounted in your exhaust system per the directions. We opted to use a weld-in bung with our setup, but a clamp-style adaptor is included with the Sniper kit.

The self-learn function is great at helping to get the car going and will keep a safe tune-up in the ECU, but it won’t be the most powerful tune-up. For those who want to take more control of their engine’s tune, you can download the Sniper software from Holley to make very precise adjustments to every parameter.

“The software allows for real-time tuning changes using the USB dongle. The learn table populates and can be transferred to the fuel map with a click of a button, which changes the fuel VE Table. Smoothing can be done to smooth out VE tables and Spark Tables with a click of a button in the software. There are 3D color graphs that allow you to see a visual of the fuel VE table and spark table, so a user can easily see peaks and valleys that can cause drivability issues. Even the startup and temperature enrichment tables are completely programmable,” Matthew explains.

The Sniper software is actually fairly easy to use and understand. There are plenty of tutorials available online to help you make changes to the tuneup if you want.

When the data-logging function is activated it records directly to the SD card in the Sniper’s handheld touch screen. The data logging feature is filled with options that are very useful to any racer who wants to monitor the health of their engine while trying to maximize performance.

“Included in the data-logging feature is a live orange dot in the Sniper EFI tables. This allows a user to see exactly where in a table the engine is at and identifies the place to change if the user desires. There’s also an overlay feature that shows the whole area of the tables that the data-log is displaying where the engine spends time,” Matthew says.

The data-logging software is easy to use and lets you look at many different items to see how your engine is doing after a run.

Each time you activate the data-log, the file is saved to an SD card inside the touchscreen. The files can be opened in the Sniper software and provide a treasure trove of information that you can use to tune your engine. When the logging is activated it collects data on RPM, fuel flow, target AFR, actual AFR, ignition timing, and other items. All of these can be laid out on the graph and examined in several different ways based on what you’re trying to learn from the previous pass.

Going into more detail, Mathew explains some of the other functions the data log offers.

“The data log records parameters like RPM, TPS, AFR, Target AFR, Coolant temp, manifold air temp, and MAP, just to name a few. Any ground inputs are included, along with nitrous and boost control parameters in power-adder applications. The data log compare feature allows you to view two data logs at the same time, compare an earlier run to the latest run, or help determine why a car may have picked up or slowed down based on the RPM trace, or TPS.”

As you can see, the Sniper EFI Stealth 4500 is a great way to swap your carbureted induction system over to an EFI system. It makes the entire swap process easy, with straightforward wiring and only requires you to upgrade the fuel system on your car to handle EFI. The Sniper EFI Stealth 4500 also provides users with plenty of tuning and monitoring options to make their EFI experience more enjoyable.

In the second part of this series, we’ll take a look at what kind of ignition is required to run the Sniper system and then we’ll put it all to the test at the track.

Article Sources

About the author

Brian Wagner

Spending his childhood at different race tracks around Ohio with his family’s 1967 Nova, Brian developed a true love for drag racing. When Brian is not writing, you can find him at the track as a crew chief, doing freelance photography, or beating on his nitrous-fed 2000 Trans Am.
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