Deep Dive: Holley Terminator X For The Gen III Hemi


Deep Dive: Holley Terminator X For The Gen III Hemi


Originally launched in late 2019, the Terminator X and Terminator X Max engine management systems for Gen III Hemis took lessons learned from the development of Terminator X systems for GM’s family of LS-based V8s from a few years prior and applied a similar approach.

“The main premise was to remove the element that causes a lot of hassles when swapping a modern Hemi into a vintage Mopar – the factory ECU,” Matthew D. Lunsford of Holley Performance explains. “When you do that, you get rid of the variable that requires you to rewire and remap that stock ECU, and doing that takes a lot of potential issues out of the equation.”

Hooker BlackHeart Gen III Hemi Dakota R/T test mule

If you are swapping a Gen III Hemi into an older vehicle (like Hooker BlackHeart's swapped 1999 Dodge Dakota R/T development mule), Holley's Terminator X software will take the pain out of engine management.

Modern Muscle and the Restomod Revolution

What kind of tuner will I need for a Gen III Hemi swap?

Holley engineers continued to develop the system and its capabilities after its debut, adding the option to control for variable valve timing (which can be found on any Hemi from 2009 or later) just prior to MoParty 2020. “VVT can be a big deal – when you plug it in or unplug it, you see a change that can be upwards of 100 horsepower,” Lunsford notes. “So it was really important to us to support that for the folks who’re using those later engines.”

Holley also offers a range of swap kit components like headers and engine mounts for folks who’re dropping late model Hemis into vintage Chrysler platforms to make these projects as painless as possible, and these Terminator X engine management systems take that notion a step further.

What kinds of vehicles can I swap a Gen III Hemi into?

“For anybody wanting to a late model engine swap – it doesn’t matter if it’s a Ford, a Chrysler product, or a GM product – they’re normally going to have to take the factory ECU out of that late model vehicle and have someone flash a tune into it and recalibrate it so that it won’t care about the fact that the Body Control Module isn’t plugged in, and so on,” says Lunsford. “And then they’re going to need to have a harness built that only uses the functions that make the engine work. So the complexity of doing a late model engine swap in an old school vehicle is definitely tougher with the OE ECUs.”

But with more and more Gen III Hemis out in the wild these days, the appeal of putting modern Mopar power into an old school hot rod or muscle car has grown in turn. “These engines are becoming very inexpensive,” he points out. “You can go to a junkyard and buy a complete, running 5.7-liter Hemi for about $1500, or a 6.4-liter Hemi for around $2500. And what you’re getting is something that makes nearly 400 or 500 horsepower in stock form that’s got the reliability, drivability, and efficiency that modern technology brings with it. So it’s a pretty incredible upgrade for somebody with a classic car with a 383 or even a 440 who might have needed to go through the engine anyway.”

Gen III Hemi Terminator X ECU mounted

Holley EFI accessories are plug-and-play with Terminator X and X Max ECUs. Gauges, shift lights, Pro Dashes, and more can be used. Drive-by-wire and electronic transmission control is available with the Terminator X Max.

Developing A Purpose-Built Solution

Lunsford tells that one of the biggest considerations when developing these systems is ensuring that the harnesses will work in a variety of applications, and that if there’s a certain unique feature on an engine, it’s accounted for. “The harnesses in the Terminator X kit are actually derived from the Dominator systems – we already had Gen III Hemi support through Dominator and HP long before Terminator X. So we adopted those harnesses and also made a few changes along the way in order to support the VVT and SVR (short runner valve) features.”

He also notes that the other thing you really need to pay attention to in the development of a system like this is the intended application. “This is for the guy who doesn’t make a living as a tuner. They want to have the ability to install this, answer a couple of basic questions, and make the engine run. And that’s why the Calibration Wizard is a huge deal.”

Gen III Hemi Terminator X Calibration Wizard

Using the Calibration Wizard on the 3.5-inch display, it is easy to get started with the initial setup, no laptop required. Just answer a few questions about your engine and the wizard will create a base map and start self-tuning from there.

Based on the answers provided by the user, the system automatically builds a calibration for that engine using data collected from Holley’s extensive research and testing. “5.7s, 6.4s, early 6.1s, later 6.1s – we spent countless hours on the engine dyno with all of them and built calibrations so that the end user would have success with these systems. We put them through a wide variety of different scenarios that are similar to how someone would use the engine in the real world to make sure it will be both dialed in and reliable.”

And part of that reliability comes from engineering a system that’s designed to take the factors into account that are inherent to an engine swap project. “The factory Gen Hemi III ECU requires connectivity and communication from other modules that aren’t required to make the engine run,” says Lunsford. “That could be a body control module, it could be a door lock actuator, a fuel pump module – it could be a number of things. So if you don’t take all of those parts off the donor car and put them in the vehicle you’re swapping the engine into when you’re using the factory ECU, it may not allow the coils to fire spark. So it would potentially run in a limp or anti-theft mode, or something along those lines.”

Gen III Hemi Terminator X Diagnostic LEDs

Eight built-in multicolor LEDs allow you to quickly identify any potential system issues or to simply monitor the system health, just at a glance.

And tuning a factory ECU can be a project in and of itself. You have to have the tuning equipment and the knowledge to do it – or hire someone who does – in order to do that work via HP Tuners, EFI Live, or similar software. You also have to be able to wire that ECU with proprietary connectors, which means either building a wiring harness from scratch or taking one out of a donor car and adapting it to your application, the latter of which would require changing wire lengths and determining which wires you need and which you don’t.

“With the Terminator X you have one harness that goes on the engine, and one harness from the engine to the ECU – that’s it,” Lunsford says. “You also have the ease of a calibration wizard to get it started and running, and you have free software that allows you to plug in a laptop and make changes to any and all parameters of the ECU whenever you want.”

Terminator X ECU Gen III Hemi VVT and SRV Control

Upgrades and Applications

Support for the VVT and SVR engine features are offered as optional extras for the Terminator X kit. The logic behind this is to make sure that these systems remain affordable instead of simply raising costs across the board in order to include components that are only applicable to specific engines. That way customers get everything they need and nothing they don’t.

Gen III Hemi Gauges, Dakota

Monitoring the Terminator X system and your Gen III Hemi's health while behind the wheel is easy, thanks to Holley's line of Pro Dashes. In addition, companies such as Dakota Digital offer modules that speak with Terminator X.

The Terminator X Max follows the same logic. These Max systems come with all of the features and benefits of the standard system but also have the added functionality of allowing you to run your Gen III Hemi via drive by wire – like the factory does – which means you don’t have to change over to a drive-by-cable throttle body to get up and running. Max systems also provide transmission control for Chrysler’s 46RE four-speed automatic gearbox, and support for additional late model Mopar transmissions is currently in development.

“The kit is universal in terms of platforms,” Lunsford says. “You’re buying it for the engine that you’re going to use rather than the vehicle it’s going in. We’ve seen these in everything from early '70s Challengers and late '60s Chargers to D100 and W100 trucks. It fits great in all of them, and you have enough harness length to decide where you want to mount that ECU. The length of the ‘trunk’ of the harness is pretty long, so you have the ability to put the ECU inside the cab of a truck, under the dash in a car, under the hood – wherever you want it. And from the flywheel forward, the engine harness fits very nicely.”

MoParty 2021 - Grand Champion Cherokee

Gen III Hemi power in a plug-and-play form is yours with Holley Terminator X. Why mess around with all the factory control units and wiring when you can have all the controls routed through one ECU?


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