Although Sniper EFI retrofit systems have seen quite a bit of success since the debut of 4150 4BBL model and the array of design variations introduced thereafter, there was a notable gap in support that the Sniper team wanted to address. “On a naturally aspirated engine, you could only use them with a certain amount of horsepower before they would run out of airflow,” says Holley Performance fuel injection systems engineer Matthew Lunsford.

“Much like the evolution of carburetors from the 4150 to the 4500 to get more fuel and air in them, the Sniper EFI line has developed similarly. In the end it was kind of a no-brainer. We saw the success we had with the 4150 and figured we should open this up to the guy that’s bracket racing with a 540ci mill or running in Top Dragster with a 632 – the folks who’re competing with engines making a significant amount of horsepower that can’t use a typical Sniper system.”

Some racers at this level of competition are hesitant to make the switch from carburetion to EFI because of the changes that are normally involved, along with the potential need to re-work their combination to get back to an established consistency and performance level. And that’s the person this system is designed for, Lunsford says. “The goal was to allow these traditional racers that are dyed-in-the-wool carburetor guys to be able to easily move into the EFI world.”

While old habits and proven strategies can be hard to shelve, the advantages offered by EFI systems like the Sniper Stealth 4500 EFI can take an already-effective race program to the next level. Let’s dig into the details.

Easy Swap, Big Benefits

The Sniper Stealth 4500 EFI system is modeled after the Gen III Dominator carburetor and uses the same mounting points for the air cleaner flange.

The Sniper Stealth 4500 EFI system has a 2⅛-inch throttle bore and is outfitted with eight 100lb/hr fuel injectors for a total of 800lb/hr fuel flow. That allows the system to support between 800 and 1,500 horsepower with a gasoline-fed, naturally aspirated combination, or up to 1,250 horsepower with forced induction. And as with other Sniper systems, the Stealth 4500 EFI can be thought of as a carburetor replacement by the nature of its design.

“Since it’s a TBI unit you don’t have to change your intake, you don’t have to change your fuel plumbing situation, and it will work with the existing ignitions that are typically found on these race cars while providing all these extra features that our EFI systems offer,” says Lunsford. “Now you have all this capability you didn’t have before, like data logging and closed or open-loop fueling.”

An external regulator like the Holley Dominator EFI Fuel Regulator is required to maintain proper system pressure.

In a closed loop system, fuel is injected based on the amount the ECU asks for and the air/fuel ratio is then measured by the EFI system’s oxygen sensors. That data is then compared against what the ECU’s target ratio is, and based on that, the EFI system automatically adds or subtracts fuel as needed to match that target ratio as closely as possible.

“It’s basically a feedback loop,” Lunsford says. “Whereas with an open loop setup, you tell the ECU that you want a certain amount of fuel regardless of what the oxygen sensor reads, and it delivers it without any variation – there’s no feedback element. Consistency is huge in the bracket racing world, so if you have a system that can constantly adjust for changing conditions like a feedback loop can, it can be a big asset because it can keep the car right where it’s supposed to be by adjusting for air temperature, barometer readings, and everything else. But you also have the guys who are used to tuning their setups, and have been doing so for years and years. An open loop system can be useful for that approach because you know the engine is getting the same amount of fuel no matter what, so you can dial in the car around how the air changed or some other factor. If you run the system in an open loop, it acts just like a carburetor in the sense that it’s not going to change your tune as it goes down the race track.”

And that, in turn, makes the Sniper system easier to learn and get accustomed to.

The installation itself follows a similar theme. “With the most basic style of install, there’s only four wiring connections required – power and ground directly into the battery, a switched 12 volt wire for the ignition, and an RPM signal wire that would come from an MSD box, or something along those lines,” he notes. “This EFI system will work with any ignition system out there, and it will control the timing of most ignition systems with the appropriate distributor. That can be magnetic pickup MSD distributor, a Holley dual sync distributor, or a Sniper Hyperspark distributor.”

More Than Just Fuel Injection

Of course the Sniper Stealth 4500 EFI system boasts a laundry list of standard features like progressive or non-progressive single-stage of nitrous control (dry or wet), integrated closed-loop boost control, and the ability to read three additional 0-5v sensors for things like oil pressure and fuel pressure. But it doesn’t end there.

“It also datalogs to the 3.5-inch hand held display so you have that information after every pass,” Lunsford points out. “And it has the ability to be used with a Racepak or any of the Holley digital dashes, so now you can have a monitor in your race car and view any of the parameters that the Sniper sees.”

Pairing the Sniper Stealth 4500 EFI with a distributor like the Holley Dual Sync allows the fuel injection system’s ECU to also control ignition timing, which significantly expands the EFI system’s capabilities.

And with the potential for the system to control the ignition as well as the fuel, the Sniper Stealth 4500 EFI can bring some other cool features into the mix as well. “Typically you would have a locked out distributor on an MSD box, and it would be set for your wide-open throttle, full advance timing,” Lunsford explains. “That might be 34 or 36 degrees, and that’s really hard on a starter. But by using the timing control in the Sniper, we can reduce the timing while cranking the engine to prevent that kind of wear. You also have the ability to retard the timing at launch so that you don’t break traction, or if you have a throttle stop, you can change the amount of timing you’re using when the throttle stop is active to change how the car behaves. You can also set it up so that, at the push of a button, the system takes timing out down the track if you’re bracket racing and need to scrub off some speed.”

With nitrous and boost control, the Sniper can also be programmed to strategically remove and add back timing as needed. “Having the integrated timing control allows you to build a curve based on exactly what your engine wants,” says Lunsford. “You just can’t do that with a locked out distributor.”

It all adds up to a motorsport-ready EFI system that offers sophisticated capability while taking racers’ habits and needs into consideration at the fundamental level. “We’re constantly evaluating what our customers want, and we do our best to match that demand.”