Carb vs. EFI: Holley Terminator X Stealth 4500 EFI Bests Carb on the Dyno

01/28/2021
10 min read

Carb vs. EFI: Holley Terminator X Stealth 4500 EFI Bests Carb on the Dyno

01/28/2021
10 min read

Mike Thompson of TNT Performance in Owego, New York, knows a thing or two about going fast. A drag racer since the age of 16, Thompson has long been an advocate for the virtues of fuel injection at the strip. “I got involved with Holley EFI through Monte Smith back in 2010 or so after checking out a seminar at the PRI Show,” he explains. “I used to race X275 with a heads up, small-tire car, and at a certain point I decided I really wanted to go to fuel injection. It took a few years to really get it all together, but I’ve had great success with it. I also recently helped Ron Rhodes make the switch, and he has set a number of records since.”


Judging by the influx of new clients coming into TNT, folks have been noticing. “Some of them are the hardcore carburetor guys who like to put stuff on the dyno – they’re looking for numbers,” Thompson says. “One of my buddies asked what I thought about the Terminator X 4500, and I suggested that it was something he should try.”


And that’s where Chris Cobb of Dynotune Engineering in Paris, Tennessee, comes in. “I met Chris through a friend,” Thompson tells us. “And he reached out to me and explained that they were looking at different EFI systems and wanted to some back-to-back comparisons on an engine they had in the shop. Chris is very familiar with carburetors in these kinds of applications, and carburetors typically tend to make a little more power than fuel injection. That’s the theory, anyway.”


Cobb and his business partner Brian Bishop have become specialists in unbiased engine performance testing over the past decade, working on an array of power plants for circle track, drag racing, street, and marine applications. “We were in the process of putting together a 598ci big block Chevy for a local bracket racer,” Cobb says. “I’d originally talked him into getting a Sniper 4500 EFI kit in advance so I could start testing it on other engines to get more familiar with the system. We ended up putting it on an SB2 engine combo and it not only ran flawlessly, it also made about 12 more peak horsepower than the well-thought-out carburetor we had swapped out. That definitely got my attention.”


Still, Cobb noticed that the Sniper system had some limitations that he wanted to address before bolting an EFI system up to the 598 BBC. “The Sniper is kind of an all-in-one design, and we had some concerns about potential RF noise with a system that has the ECU on the throttle body.” So after a chat with their client, they started looking around to see what their options were for a system with an external ECU.


“We get a lot of street/strip cars that come through TNT Performance, and I’ve always liked the Terminator X design for those kinds of applications,” Thompson says. “It’s very adaptable. You can take the Terminator ECU and run a throttle body or multi-port, they work great with the LS platform, the Fox-body stuff – it’s really versatile, and that’s the main thing for me. It works with a lot of different applications, and not everybody needs all the extra features of a full-fledged Dominator EFI setup.”


So when Cobb reached out and explained that they had this 598 big block that they wanted to do some testing with to see if there would be any gains with an EFI system, Thompson suggested that Terminator X Stealth 4500 would be well-suited to the task. “With this engine it’s more than enough – this isn’t a heads up Pro Mod drag car, so he doesn’t need to be able to read four shock sensors, eight O2 sensors, and so on. He needed a handful of things like a G-meter and a driveshaft sensor, along with the requisite engine sensors that the EFI system needs to run properly. It’s a system that’s perfect for the sportsman racer.”


Cobb started the comparison tests off with the carburetor setup, a 1450 CFM large-bore billet carb. “It ran extremely well on several different engines,” he notes. “And on this particular engine, we worked on it for four or five pulls to get it to perform at its best to get those numbers before we switched over to the EFI system.” The end result with the carburetor were peak numbers of 1005 horsepower and 833.7 pound-feet of torque before making the switch to the Terminator X Stealth 4500.

Terminator X 4500

The Terminator X Stealth 4500 Kit, which can be ordered in polished (550-1070) or the pictured black finish (550-1071). The Terminator X Stealth 4500 is outfitted with eight 100 lb/hr injectors that can support 1,500 naturally-aspirated or 1,250 forced induction horsepower.


“For the initial pull with the Terminator system, we set the target air/fuel for wide open to be 12.8, and right out of the box it was making equal horsepower to the carburetor,” Cobb says. “After that we moved around the target air/fuel to clean up the spots where the system was correcting. Typically an engine needs more fuel at peak torque, so we richened up the target air/fuel between 5500 and 6500 RPM. That brought the torque numbers to about equal with the carb, and from 7000 to 7500 we leaned out that target air/fuel to 13.1 to really make it happy.”


When all was said and done, the Terminator X Stealth 4500 EFI system yielded peak numbers of 1018.8 hp, 833.8 lb-ft. “We only did four pulls with this system,” Cobb points out. “I think that we could have made even more power with a bit more time on the dyno, but ultimately this is somebody else’s engine we’re working with, and they were gracious enough to let us try this out.”


Along the way, Thompson helped with testing from New York using remote desktop software that allowed him to see the data as the pulls were made and collaborate in real time with the team in Tennessee. “Mike was instrumental in this,” Cobb says. “He tuned the fuel map to get the engine to idle how and where we wanted it, and he was able to look at the data log and overlay it on the fuel map to see where corrections would really provide a benefit.”


And that ability to manipulate the air/fuel ratio with just a laptop and software really illustrates how EFI systems like the Terminator X are changing the game for drag racers. “With a system like this, you can just target certain things and make it do whatever you want, whereas with a carburetor, you’re basically just along for the ride,” Thompson says. “No matter what you do with it, it’s going to be a compromise somewhere. You might be able to get one end of the powerband where you want it, but the other is essentially stuck where it is.”


And for Dynotune Engineering, that added capability equates to a happy customer. “I thought the Sniper 4500 was a good system that would offer more than a carburetor with a good ignition system,” Cobb says. “It was Mike’s input that pointed us to the Terminator X Stealth 4500 to step things up – you have the divorced ECU, you have more control, and the right set of features for a sportsman-level application. For these naturally aspirated engines with no power adder or limited nitrous, I feel like this is the Easy button.”


TermX4500 Tested On Big Block Chevrolet

Cobb started the comparison tests off with the carburetor setup, a 1450 CFM large-bore billet carb (shown). “It ran extremely well on several different engines,” he notes. “And on this particular engine, we worked on it for four or five pulls to get it to perform at its best to get those numbers before we switched over to the EFI system.” The end result with the carburetor were peak numbers of 1005 horsepower and 833.7 pound-feet of torque before making the switch to the Terminator X Stealth 4500.

TermX4500 BBC Dyno Test 2

Like the Sniper 4500, the Terminator X Stealth 4500 is a self-tuning-capable, bolt-on, 4500-flange carburetor replacement. From a design standpoint, the Terminator X differs from its Sniper counterpart in that the ECU itself is not integrated into the throttle body, allowing you to mount it everywhere you want in the vehicle.The Terminator X Stealth 4500 uses a calibration wizard similar to that of the Sniper systems. Simply input a few basic specifications about the engine on the included touchscreen handheld, and the system will create a baseline tune to get the engine up and running with no laptop required.

TermX4500 Air cleaner flange

The Terminator X Stealth 4500 is outfitted with a Gen 3 Ultra Dominator-style four-bolt air cleaner flange that allows for a wide variety of different air cleaner options.

Terminator X 4500 peak hp numbers

A comparison of the peak carburetor horsepower numbers (Sweep 5) and the Terminator X system (Sweep 11).

Terminator X 4500 peak torque comparison

Here’s a look at the peak torque numbers from those same dyno pulls.

Termx4500 Output Graph Comparison

This graph illustrates the output differences between the carbureted setup (Sweep 5) and the Terminator X Stealth 4500 (Sweep 11). Note that the Terminator X system not only makes more peak HP, it also makes more horsepower and torque from 6200 to 7400 RPM.


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