Installing Holley’s Sniper EFI Is So Easy, Even We Can Do It

Have you checked out any of the many Internet forums recently? One discussion that seems to be reoccurring, is about upgrading to electronic fuel injection (EFI). It used to be thought that adding EFI to a classic, carbureted vehicle, required a degree in rocket science. But now, many manufacturers have jumped head-first into the realm of developing an EFI system that does not require a laptop – or the aforementioned degree.

Sniper EFI

The Quadrajet has been on the Cheyenne since it left the factory. I’m not sure if it’s ever been rebuilt, but the cost of rebuilding it and the fact that parts were missing was a good reason to upgrade to the Sniper EFI.

Once such entry is Holley’s new Sniper EFI. With a retail price of just under $1,000 (depending on options chosen), the kit is touted as a bolt-it-on-and-go solution for an easy EFI upgrade. Personally, I’m an old school guy and have not had a lot of experience with fuel injection. I’m a carburetor guy at heart, but since a lot of you ask me what I think of the kits available, I decided to give one a try.

The Sniper EFI kit I am using for this install is rated for engines developing up to 650 horsepower. That’s actually more than sufficient for my truck. Even if I build another engine in the future, the Sniper kit will be suitable to use, as I don’t expect to build anything with more power. I am told there is a hotter, eight-injector system being developed by Holley, but a release date has not been announced. That injector-heavy unit should be able to support engines making up to 1,200 horsepower. I’m also told it is being designed to handle a blow-through supercharger or turbo.

Since I really have no background in EFI tuning – and even less knowledge of computer programming, if I was going to take this leap, I needed it to be simple. Sure, I can handle the mechanical aspect of an install: wiring, plumbing of a fuel system and such, but if computer tuning is required, that is a rabbit hole I am not willing to enter until I got some education about all aspects of EFI do’s and don’ts.

Sniper EFI

Holley says the Sniper EFI will work on a spreadbore intake, but I still used a spacer/adapter.

Lucky for me, the Sniper EFI doesn’t require me to upload and adjust fuel maps or tables. It doesn’t require understanding how the Inlet Air Temperature (IAT) or Manifold Absolute Pressure (MAP) sensors work. All it requires me to know, is how to hook up a couple of wires, plumb some fuel lines, and follow directions. Although some would say that following directions is somewhat new to me, I can do that.

Why Do This

I know what some of you are thinking, “why remove a perfectly good carburetor?” In all honesty, the carburetor I planned to replace wasn’t a perfectly good carburetor. As far as I know, the fuel miser on the Cheyenne has never been rebuilt. Most recently, the choke was sticking and not allowing the fast-idle to come down and fuel mileage was not as good as I would like. In general, it needed a rebuild.

The sniper does have the dual bolt-pattern for use on square or spreadbore configurations. You just need to check and make sure the throttle blades don’t hit the intake manifold. – Keith Jessee

I initially planned to give the Q-jet some attention, but after I removed it from the engine, I noticed a few glaring issues that would need to be addressed. For starters, there were parts missing. This isn’t a big deal, as I could probably find them at a swap meet, but that generally requires buying another complete carburetor just to get a few small parts. Also, the throttle-shaft bores were worn. This could be remedied by either having a machine shop install bushings, or again, buying another, used, replacement body. Even though I could handle the rebuild, farming out the machine work for the baseplate was another expense.

The Sniper throttle body has a built-in fuel pressure regulator (right). I ran the feed line from the tank, through the supplied filters and Walbro pump to one of three possible inlet positions (left). I then plumbed the return line from the tank to the regulator (left) and I was done. Dropping the fuel tank to install a return line is the hardest part of the install.

If I wanted to buy an already rebuilt carburetor, I was finding reputably rebuilt units could cost anywhere from $250 and up. While that might not be as substantial of an investment as a new Sniper EFI, I started to think that the benefits of EFI over carburetion is definitely a reason to consider it.

Sniper EFI

The kit comes with the needed throttle bracket and optional kickdown-cable bracket. The C10 already used an intake-mounted kickdown-cable bracket so I only used the throttle-cable bracket. The stock Q-jet throttle-cable bracket would not work.

The Sniper EFI throttle body is a bolt-on replacement for a square-flange carburetor. Whether unfortunate or not, my C10 had a Q-jet (I can hear the Holley fans cringing), which is a spreadbore style. The folks at Holley say the throttle body can be bolted to a spreadbore intake, or a spacer of some sort can be used.

“The Sniper does have a dual bolt-pattern for use on square or spreadbore configurations. You just need to check and make sure the throttle blades don’t hit the intake manifold. If they do, you might get away with using a thick gasket or a thin spacer. Using an adapter or spacer really shouldn’t give you any issues,” stated Keith Jessee, of Holley Performance.

Sniper EFI

The throttle body has two hard-wired connectors that attach to supplied wire harnesses. One is for the main and switched power supply, and the one shown here is for accessories like fan controllers and nitrous initiators. Since I didn’t need the accessory harness, I called the Holley tech line, and they told me I could simply seal the unused connector and tuck it away. I used a piece of the foam from the packaging, and then wrapped the connector with electrical tape.

I decided to use a squarebore to spreadbore adapter/spacer from Summit Racing to bolt the throttle body to the intake. I wondered if adding a small spacer for an application like this would have any adverse effects, but according to Keith, “Using an adapter or spacer really shouldn’t give you any issues. Considering you’re using a factory-style intake, the added plenum volume would only amount to a roundabout hill of beans. That’s just because the factory spreadbore intake probably isn’t going to respond to a change like that hardly at all,” Keith said.

The Parts List

With the decision made to go EFI, I ordered Holley’s PN 550-511K Sniper EFI Master Kit. This kit comes with everything you need to convert your carbureted ride to EFI: throttle body, throttle body-mounted ECU, complete fuel system consisting of fuel hose, in-line fuel pump, filters, the necessary hardware and bulkhead fittings to return fuel into the tank, touchscreen controller for setup, and an oxygen sensor with a clamp-on mount. I’ll let you know up front, this master kit costs $1,250. The advertised $999 price tag you often hear talked about is not for the master kit and does not include the fuel system.

Sniper EFI

The toughest part of the install was to remove the tank for the installation of a return line.

As I said, the throttle body is designed to simply bolt to the intake, and you will need to install the supplied temperature and O2 sensors. You can install the temp sensor in the intake or the cylinder head, it really won’t make much difference, provided you have sufficient coolant flow. I mounted the temperature sensor in the intake since the port in the cylinder head was being used for the Dakota Digital temperature gauge in the dash.

Sniper EFI

My C10 has a sending unit with three ports (feed, vent, return). I didn’t use the return port, because Holley recommends a 3/8-inch line, and the return line is 5/16-inch.

If you’re worried about having to weld a bung into your exhaust for the O2 sensor, worry no more. Holley supplies a clamp-on bung that only requires you drill a 3/4-inch hole in the exhaust. Once the hole is drilled, install the bung with the supplied stainless-steel clamps. It was easy.

Sniper EFI

Since the return port on the sending unit was too small, I installed the Holley return line as per the instructions. Be careful and use proper safety procedures when drilling the hole you will need for the fitting. If you create a spark, boom could be the operative word. If your sending unit is a two-port and has room, you could add the supplied fitting to the sending unit.

When it comes to the wiring, again, easy is the operative word. All you need to do is connect four wires to your vehicle. Just connect the proper wires to the battery positive and ground, tach signal, and a switched 12-volt source. The 12-volt source wire is the one that seems to get people into trouble. This pink wire needs to be connected to a power source that is hot when the key is turned on, and, when the engine is cranking, and when the engine is running. This is called a true ignition source. The problem arises when this pink wire is connected to a switched-only source. In other words, the wire does not get voltage as the engine is cranking.

Recommended Baseline AFR Values For Naturally Aspirated Engines

Idle / Light Cruise: 14.0 – 15.0 AFR
We all know what idle is, and when you shift into gear and drive at a low mph this is light cruise.  At these times, a 14.6 AFR is considered industry standard, but your engine might like a leaner or richer AFR.

Cruising: 14.0 – 15.5 AFR
Cruising is where your engine will spend most of its time.  If you prefer better fuel mileage, then run a slightly leaner mixture. Most stock to slightly modified engines will run fine with an AFR of 15, and deliver excellent fuel mileage. If you prefer better performance options, then you can run an AFR of 14.0 to around 13.0.

Wide Open Throttle (WOT): 12.5 – 13.5 AFR
Driving with the throttle pedal against the floor while in gear will bring you into a wide open throttle driving condition. It is a good idea to run a richer AFR to not only avoid detonation, but also get the best performance. Best performance for most vehicles is with an AFR around the 12.5 to 13.0 range. But, having an AFR that is too rich will have the opposite affect and decrease your performance.

Acceleration: 12.0 – 12.5 AFR
Getting up to cruising speed or getting ready to pass someone is considered an acceleration condition. You will typically like to run a richer AFR here to get the best performance, and not cause detonation. In most situations, the best performance for most vehicles is around 12.0 AFR. Going too rich will cause a “bog” or sluggish increase in speed.

The wire harness for powering the unit is pre-made, and even includes a relay and fuse. An additional wire harness is included if you want to run a CD-ignition box, cooling fan, and nitrous relay, as well as fuel pump and tachometer outputs. Just use the connections you need and tuck the rest away. In fact, I didn’t even need to use one of the factory-supplied harnesses since this is a simple install without nitrous or extra cooling fans. I simply sealed the wire harness from the throttle body with a piece of dense foam and then taped the end to seal it from the elements. If I ever add accessories like electric fans or nitrous, I just plug in the harness when needed.

Is It As-Described?

Did it bolt on as expected? Yes. I handled all aspects of the install in my driveway with the truck on jack stands. That being said, lowering the fuel tank is required, and I plumbed all new fuel lines. The Sniper Master Kit does come with rubber fuel line, but I chose to run metal lines for my application. What’s more, I didn’t have to buy anything outside of the kit to get it to work.

Sniper EFI

Although Holley sends enough rubber fuel line to complete the install, I wanted to use steel lines where ever I could. That surely added to the amount of time it took me to complete the install.

I have heard of guys installing this kit in a couple hours, but I’m not sure how they did it? Unless they already had a dedicated EFI fuel system, I’m not really sure they did. They most definitely didn’t install the master kit. I will not say they cut corners, but… It took me the better part of a full day to complete the install. That includes removing the fuel tank and completely re-plumbing the fuel system. I did stop quite often to take pictures as well, so that added some time. Regardless, plan on it taking at least a complete day. If you have a lift, I’m jealous.

Sniper EFI

The main 12-volt and ground wires should be connected directly to the battery. This guarantees a constant 12 volts to the system.

After everything was plumbed and connected, I hit the key and followed the prompts on the touchscreen to set the base tune. All that was required was to enter the engine’s cubic-inch size, cam type (stock, street/strip, or race), ignition type (coil, CD, etc.), and the target idle-rpm in the setup wizard.

Sniper EFI

With the fuel feed line attached, the stock air cleaner would not fit. Luckily, I had an open element breather in the garage.

Once the information was uploaded, I took a deep breath and thought, “here goes nothing.” I turned the key on to prime the fuel system, and when I hit the starter, the bone-stock 350 fired immediately! The only thing that I was not a fan of, was the initial Inlet Air Control (IAC) settings. They had the engine ramp up to 1,700 rpm for 4 seconds, and then slowly come down to my preset idle. I’ve since learned that this is easily adjusted, but I am waiting until the system has had sufficient time to “learn” what it needs. Remember, this is a self-learning system, let it do its thing. There were no issues with start-up and idling, and I never touched the gas pedal, unlike with the previous Quadrajet that needed constant input when cold.

“The unit operates in “open loop” when under 160 degrees, which means it isn’t modifying the learn table. It will still modify the fueling of the engine to achieve the target AFR, though. There are coolant temperature enrichment tables you can modify to tailor it to suit your engine, but our base tables are generally pretty close because they take engine displacement into account,” According to Keith.

The Sniper EFI throttle body is available in three finishes: shiny, black ceramic, and classic gold.

Choose Your Ratio

One of the great features of the Sniper is the ability to set your air/fuel ratio (AFR) where you want it. A Stoichiometric air-fuel ratio is 14.7, which is the ideal ratio for “exhausting” the lowest emissions. But, it is not the best ratio for building horsepower. Engine tuners used to always try to obtain a 12.5 AFR at wide open throttle, which was considered the best ratio for developing horsepower. But, with improved combustion chambers in today’s engines, and hotter ignition systems, it is widely held knowledge that an ideal ratio is now around 12.8 to 13.2. Since I was able to choose my desired air/fuel ratio, I set it as follows: 13.1 at idle, 14.2 at cruise, and 12.9 at WOT. The nice thing is, after some time, I can change these values as I see fit. I might do some tweaking to increase fuel mileage after the system has sufficient time to learn.

Sniper EFI

Setting up the system only requires answering a few simple questions on the hand-held controller. It is self explanatory.

In case you were wondering what the air/fuel ratio numbers mean, here’s a little help. The lower the AFR, the richer the mixture. The higher the AFR, the leaner the mixture. An engine that is properly tuned and driven under normal road conditions has an air/fuel ratio that is constantly changing. At idle, cruising, and under light loads, a somewhat lean air/fuel ratio is desired. But, when the engine is required to develop substantial power, richer air/fuel ratios are used. All numbers are with the engine at operating temperature.

What’s To Come

As I am writing this, The Sniper EFI has been on the C10 for a little more than a week. I am amazed at how the drivability has improved over the carburetor. The truck runs smoother than it has since I first bought it. Also, I have even noticed the truck gets roughly 1 ½ to 2 miles per gallon better fuel economy. While that might not seem like a lot, remember, the system is still learning, and I might even be able to adjust things to improve upon those numbers. Since the Cheyenne is my daily driver, over the course of a year, that mileage improvement can really add up.

Once everything is connected, start your engine! Once the vehicle reaches normal operating temperature (above 160 degrees), the Sniper system will start learning what your engine needs. It’s really that simple.

I did learn one thing after some time driving. Without baffling in the fuel tank, if the truck gets to just below a ¼-tank of fuel, fuel slosh can be a problem. Basically, under various driving conditions, the fuel travels away from the pickup and the engine occasionally hiccups as the supply is temporarily gone. To remedy that, I can either make sure the tank never gets below ¼ tank, figure out how to add baffles to the tank, or I might have to look at other options to fix the issue.

That being said, I am more than pleased with the improved drivability and increase in fuel mileage. The system is still learning, and I am confident that fuel mileage will continue to improve as the system “dials in.” I even plan to eventually do some learning of my own and tweak the system parameters after it has settled-in on what it needs. My theory is this, I’ll change a setting, and if it doesn’t help, I can always go back and set it where it was. Changing settings is easy, just use the touchscreen.

This isn’t the last you’ll hear about this Sniper EFI install. Something like this can show long-term benefits, so I plan to give you guys a future update as things progress. That way, you too can see the progress and find out whether Holley’s Sniper EFI is for you. So far, if you’re even thinking about upgrading your classic to feed from EFI, the Sniper EFI should be a definite consideration.


After a few weeks of driving the truck with the Sniper EFI and doing some simple tuning via the hand-held controller, I thought I would let everyone know the results. If you’re interested to find out what I did, and my thoughts after some seat time, click here.

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About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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