Holley Sniper or Terminator X Stealth: A Buyer's Guide (2023)

Sniper or Terminator X Stealth?

Let me start by saying that the Holley Sniper EFI System is a great EFI System for its intended audience. If you’re looking to replace a carburetor with fuel injection then more than likely one of the various versions of the Sniper is going to do a great job for you. Not just that, but it is going to excel in areas that beat the competition hands-down. The 3.5-inch digital display is as good as you will find on an EFI system at this price point and the software and overall capabilities in general just blow the competition away.

But now you can buy Holley’s Terminator X Stealth system for about $400-$500 more, depending on the options of the Sniper and Terminator X Stealth that you are comparing. That’s a decent chunk of change—and roughly 50% more than the Sniper’s base price. So you have to ask yourself, “Does the Terminator X Stealth offer features that make it a better value to me than the Sniper?” Well, let’s dig into that a bit.


Since selling our first Sniper EFI System back in April of 2016 (wow does time fly!) we have been pushing the boundaries on what this system could do. And there is no doubt that it is impressive. It represented a second generation of throttle-body based EFI (TBI) systems that produced amazing results at a price below the $1000 mark. Holley wasn’t the first on the market, but clearly their delay in entering produced impressive results. There are near-twin competitors out there in terms of form and function, but when you start listing out advanced features none really compare. Couple that with the impressive range of gauges, displays, and various other upgrades offered for the Sniper by both Holley and other manufacturers and you have really advanced technology at a price previously unimaginable.

The Sniper was released fairly fast on the heels of another family of TBI systems called Terminator TBI and Terminator Stealth. (Don’t let the lack of an ‘X’ in the last sentence slip past you. These predated the Terminator X systems by years—we’ll get to that soon enough.) The Terminator was likewise amazing and did capture some market share. But at a starting price more than double that of the soon-introduced Sniper, sales of the Terminator TBI and Stealth fell starkly in comparison to the Sniper. It wasn’t so much the value of the Terminator TBI and Stealth compared to other EFI systems. It was the tendency to compare prices with the Sniper side-by-side.

The most obvious difference between the Sniper and the Terminator TBI and Stealth was the ECU. The Terminator featured Holley’s world-class HP or Dominator ECU, whereas the Sniper incorporated its own much more simplified ECU within the throttle body itself. The price difference in the systems is simply a reflection of the cost of the ECU.

Moving Forward

So more recently Holley introduced two new ECU’s: Terminator X and Terminator X Max. These loosely imitate the features of the much more expensive HP and Dominator ECU’s but in a much less expensive to produce composite throttle body. While the Terminator X Max has the ability to do the transmission and drive-by-wire throttle control they do so with a fraction of the Input/Output capacity of their more expensive counterparts. Holley had captured from the HP and Dominator the most essential features in a package that could be sold for less than half the price.

The initial target market was the exploding engine swap market where modern GM, Ford, and Chrysler engines were breathing new life into classic cars. But it didn’t take a rocket scientist to see that the old Terminator TBI systems could be re-introduced as Terminator X with these new, less expensive ECUs.

So beginning in May of 2020, customers were presented with the dilemma we posed at the start of this article, “Does the Terminator X Stealth offer features that make it a better value to me than the Sniper?” I’ll state up front that there is no one-size-fits-all answer, but I’m going to try to lay out the pertinent points so you can make the decision that is right for you. Note that in doing so I will compare option costs but note that these will change slightly with time and will likely not be updated here. They should still be accurate enough to give you a picture of what system is best for your application.

Key Differences

Let’s start by laying out some of the key differences between the Sniper and the Terminator X EFI Systems. Since the different features will have differing levels of value to each user, I’ve just listed them here in alphabetical order:

Cab-mounted ECU – The Sniper’s ECU is inside the throttle body itself, while the Terminator X ECU is mounted remotely, most commonly inside the vehicle. Each has its benefit. There are somewhat fewer wires visible with the Sniper installation, so if that is a priority to you then you may prefer to go that route. However, by mounting the Terminator X ECU remotely, you spare it from the harmful effects of under-hood radio-frequency and electro-magnetic interference. How big a deal is this? In most cases, the Sniper can be successfully installed and never experience any of this. In others it makes the installer’s life a living hell. And you really don’t know what you will have until you install it. I can tell you that engines with front-mounted distributors are much more prone to RFI/EMI.

(Video) Answering your questions about Holley's Sniper Stealth EFI

CAN Bus Sensors – In both cases the ECUs monitor a set of sensors and then transmit this data over the CAN Bus to the displays, gauges, and laptops. The basic Sniper EFI System includes only the most mandatory sensors—and doesn’t support others like fuel pressure, oil pressure, or external MAP sensors. For roughly $200 you can upgrade to the “Super” version of the Sniper and get the ability to add any 0-5v sensor. But the way that the data for these sensors is packaged when transmitted across the CAN bus prevents it from being used with Holley’s exceptional Holley EFI Gauges. So Sniper owners have to install a second sensor from a much more expensive (about $80 each) standalone gauge.

Terminator X Stealth EFI Systems come with a fuel pressure and MAP sensor connector already wired into the main harness. And since the ECU has a port for the oil pressure sensor, one need only wire that in. Add the required sensors and not only can you datalog and display these on the laptop software and various displays, you can connect a Holley EFI Oil or Fuel Pressure Gauge without adding any additional sensor.

Customizable Software Inputs – Ok, I’m going to have to get back to you on why this is a benefit. No experience here. But Terminator X gives you 20 and Sniper gives you none. For whatever that’s worth.

Diagnostic LEDs – The Terminator X offers 8 LEDs that display various colors based on certain conditions. Based on my limited experience at this point, I’m not seeing anything here that you couldn’t find nearly as well (or better) from the handheld display. But flashy lights are cool!

Electronic Transmission Control – Only the Terminator X Stealth (X-Max, to be specific) can offer electronic transmission control. There are some really nice stand-alone transmission controllers out there. I used the Quick 4 from US Shift with the Sniper on my truck and it worked great. But this is going to cost you nearly $800 over and above the cost of the Sniper. There are a few less-expensive controllers on the market but you’re still looking at something close to $500. And it’s another thing to install and another thing to figure out and another display to watch and another thing to maintain. Or you get the transmission control version of the Terminator X Stealth for $400 and you’re done with it.

Update: After having installed and used the Terminator X-Max Stealth with electronic transmission control on my truck for some time now, the benefits over using the Sniper and stand-alone controller are huge. Starting with the fact that now I can monitor fuel economy in real time. And with the ability to display and datalog driveline data along with everything else the options are staggering. And tune the shifting based not only on TPS but also load. These benefits actually turn the proposition on its head a bit. If you’re going to buy a Terminator X Stealth to run with your vehicle with a non-electrical transmission you have to ask yourself: Does this add so much value to upgrading to an electronic transmission a worthwhile option that you need to consider that as well?

Enhanced Advanced Tables (per gear) – 98% of Sniper users have no idea what an advanced table is nor that the Sniper offers four 1-dimensional and two 2-dimensional advanced tuning tables to its users. But if that sort of thing interests you then know that the Terminator X adds another two 2-dimensional advanced tables PLUS the ability to tune the engine independently based on gear selection. Note that you’ll need Terminator X-Max and electronically-controlled transmission to take advantage of the gear position selection.

Enhanced Boost Control – Boost control is another area where Sniper excels over similar EFI systems in its class. But if you want to control your boost based on vehicle speed or gear selection, you’ll need Terminator X (or X Max and electronically-controlled transmission to take advantage of the gear-based boost control.)

Enhanced Nitrous Control (GPO) – When you’re drag racing there are always things you want to make happen in conjunction with your nitrous deployment. Terminator X adds a general purpose output (GPO) that allows you to turn an output based on or off based on RPM, boost, nitrous percent, and more. Very handy—and not found in Sniper.

Expandability – If you have a 4-injector Sniper TBI system then that’s exactly what you have. Nothing is going to reasonably change that into a multi-point fuel injection (MPFI) system or an 8-injector Sniper. But if you have the Terminator X Stealth, you could shelve the throttle body, add the appropriate harnesses, and make this into any of the different MPFI systems that one could build using that ECU. If you wanted to go to an 8-injector version, or if you wanted to go up to a Stealth 4500 TBI system, you could do that as well. None of this is to say that would be a cost effective route but things happen and sometimes you’re left with pieces of a system. With a self-standing ECU, you have options.

(Video) Holley EFI for Beginners -Where to Start! // Sniper, Terminator X, HP/ Dominator

Ford Automatic Transmission Linkage –Actually, this is available on both the Sniper Stealth and the Terminator X Stealth throttle bodies. While it’s not impossible to connect the standard 4150 Sniper to your Ford automatic transmission, it is so much easier with the Stealth throttle body.

Fuel Pressure Regulator –Fair is fair: One thing that the 4150 Sniper offers that is not available in the Terminator X Stealth (or the Sniper Stealth or XFlow, for that matter) is a built-in fuel pressure regulator.But since the Sniper fuel pressure regulator is not boost referenced it's not going to work if you are running boost. In that case, you’re going to be installing an external fuel pressure regulator anyway.

Inputs/Outputs – This could have a huge impact on your decision. The Standard Sniper only offers two ground-type inputs and three ground-type outputs, plus three 0-5v sensor inputs if you spend the extra $200+ for the Super Sniper. And that is all that many folks will ever need. And while Terminator X offers four inputs and four outputs, it's not the quantity alone that is the big deal but the types. You can connect the Terminator X to 12-volt, ground, 5-volt sensor, and frequency inputs. That means you can connect to a flex fuel sensor and customize your tune based on percentage of ethanol in your fuel stream. There are no flex fuel sensor options for Sniper users at this time.

Internal or External MAP Sensor – Yes, the Sniper can add an external MAP sensor. And the Sniper’s internal MAP sensor is 2.5-bar compared to the Terminator X’s more meager 1-bar sensor. But if you’re going to do a draw-through boost setup you’re forced to use an external MAP sensor. On the Sniper that’s going to add at least $200 to the price tag to upgrade to the Super Sniper. The Terminator X not only has a MAP sensor input on the ECU but provides a pre-wired connector for an external MAP sensor. Too easy.

Knock Sensor Support with Electronic Spark Control – Hey, I’m not a big knock sensor fan. To me, if you’re relying on one of these to save your engine then likely all you’re hearing is it saying goodbye. But if you want one you’re going to have to go with the Terminator X.

Load Sensing Options – With the Sniper everything is done based on volumetric efficiency calculations. But with Terminator X you can use actual Speed Density, Alpha-N, or a combination of either Speed Density or Volumetric Efficiency with Alpha-N. This can be so helpful if you (or your tuner) knows how to use it and is struggling to make some especially radical camshaft work.

Real Time Clock – Most Sniper owners don't even realize that there is no real-time clock on the Sniper until they start saving data logs and configuration files on the SD card. Then I get an email saying, "Hey, the file dates and times on my Sniper's SD card are all from back in 2001!" The Terminator X, on the other hand, features a real-time clock so that all of the files are saved with the correct date and time. This is so convenient. Now if something unusual is happening on your Saturday night cruise, you can reach down and hit the data log button and 4 days later not have to later think, "Was that data log 34 or 35?" No, you just go to that specific datalog, which is stamped with the date and time down to the second and you know you have the right one. Same for configuration files.

Staging Assist – Would you benefit from the ability to creep your car into the staging beams using a transbrake and a pair of buttons? Then you better get Terminator X because Sniper can’t do this without buying an external box (costing you an extra $200+).

Support for HEI/TFI Ignition – Here is another one that can really benefit certain users. Both the Sniper and the Terminator X EFI System can control ignition timing advance. Generally speaking, this is going to require you to buy a HyperSpark distributor to do this. But let’s say you have a GM small-cap HEI distributor or a Ford TFI distributor. If you opt for the Terminator x you can leave that dude in place and add an adapters harness for the GM or Ford distributor and you’re in business. That saves you the difference between the cost of the HyperSpark distributor and the adapter harness (between $150 and $200.)

Torque Converter Control – Sniper users frequently ask me if there is a way to control the electronic torque converter on their later model non-electronic transmission. Um, sort of. You can add nitrous control and sort of back-door it. But this is a standard feature on Terminator X. No back-dooring required.

(Video) Watch This BEFORE You Buy HOLLEY EFI in 2023!

Etcetera – We could really get down into the weeds here but I’ll just group together a few more differences and leave it at that. Terminator X provides a significantly more advanced dwell table (16x16 versus 2x4); Sensor scaling and safeties for RPM and Speed; Scramble boost feature.


So what does all of this mean to you? Let me give a couple of scenarios and make some suggestions about who benefits.

Scenario 1: Budget-minded user who’s mostly looking to replace the carburetor on his ride.

Too easy— Sniper 4150. In fact, I encourage folks who have no plans to make over 300 HP to go with the exceptional Sniper 2300 2-barrel and save another $100 or so. This is going to do everything you want.

Scenario 2: Show-minded classic owner who doesn’t want his engine compartment looking fuel injected or overly wired. Rear-mounted distributor

In this case, Sniper Stealth. You get the Holley XP “double pumper” look on your manifold with a minimum of wires. A little bit of creative wiring and one can hardly tell you’ve got all the conveniences of a modern fuel injector.

Scenario 3: Like Scenario 2 but front-mounted distributor.

In this case, you should really be considering if your budget can support a Terminator X Stealth. Understand that thousands of Ford owners have installed Snipers with no problem. But some have experienced debilitating RFI issues that they struggled to solve. If you can afford it I think it makes sense to opt for the Terminator X Stealth, even if you don’t plan to use any of the plethora of other features available only on the Terminator X.

Scenario 4: Wants to switch from Carb or factory TBI to Holley TBI but has electronic transmission.

Slam dunk—Terminator X Max Stealth with Transmission control. Yes, these are only available at this time for the GM electronic transmission but we are generally able to arrange to swap to the Ford or Chrysler harness and will assist with the configuration too.

(Video) Ditch the Carb and Go EFI with Holley Terminator X Stealth 4500 and 4150

Scenario 5: Power user. Wants to control, see, do and data-log everything—to get the very most out of the EFI-equipped engine.

Again, Terminator X Stealth. Holley made some very strategic omissions to get the price of the Sniper to such an affordable level while supporting just about everything the average user could want. But sacrifices had to be made. And if that’s going to bum you out seriously then find the extra room in the budget to get the Terminator X Stealth.

Scenario 6: Draw-through Supercharger application.

This one depends. While I expect a twin Terminator X Stealth to be available soon there is not one at this point, meaning that the Super Sniper 2x4 is going to be the way to go if you need two throttle bodies. If this is you then you might check to see if a twin Terminator X Stealth has been released or consider our Twin Terminator. Beyond that, you also need to consider HP. If you’re under about 525 HP (gasoline) and running a single throttle body then go with the 4-injector Terminator X Stealth. Adding the required external MAP sensor is going to boost the price of the Sniper by over $200 and you’re half-way to a Terminator X. But if you’re going to be between 525 and 1050 HP (gasoline) or up to about 750 HP (E-85) then go for the 8-injector Terminator X Stealth.

Scenario 7: Serious Drag Racer

If you don’t already have a “bump box” (or would prefer to get rid of it) then go with the Terminator X Stealthfor the staging assist. You may use the per-gear advanced table features. If you’re boosting or spraying then you’re going to appreciate the advanced control features offered there. Go with the 8-injector if you’re making over 500 HP or using E-85. If you’re making over 700 HP NA then go with the Terminator X Stealth 4500.

Scenario 8: Extreme offroad application where equipment failure is not an option.

Not a trick question but a trick answer: Instead of Terminator X go with Terminator TBI or Terminator Stealth. These use the more robust HP and Dominator ECUs. Yes, much more expensive. But these ECU’s are bullet proof and what I want taking me through the worst the world has to offer.


So you see that there is no one right answer on which EFI system is right for all cars and their owners. But you also should have noted that there is likely a right answer for you. EFI System Pro specializes in helping those with interest in EFI find exactly the system that is best for their application and to provide them with everything they need to be a success while installing it--usually right down to the last hose clamp. Contact us now if you're interested in finding the right system for your application. Or join in the conversation below. We'd love to hear your insights!


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