Holley Fuel Injection Systems Tested

Holley's Fuel Injection Offerings: A Dyno Test

Holley, a name synonymous with automotive performance, offers a comprehensive range of fuel delivery solutions. While many enthusiasts are familiar with their iconic carburetors, the question arises: does Holley also produce effective fuel injection systems? To answer this, Prestige Motorsports recently put two of Holley's fuel injection systems to the test on their in-house engine dyno, evaluating their performance on a formidable 800-plus horsepower engine. The results offer valuable insights for those considering a switch from traditional carburetion to modern electronic fuel injection.

The Testbed: A Powerful Big-Block Chevy

The engine chosen for this evaluation was a 582 cubic-inch big-block Chevrolet, a powerhouse in its own right. To ensure optimal breathing, it was fitted with Edelbrock CNC-ported cylinder heads. The compression ratio was set at approximately 10:1, a figure that allows for the use of premium pump fuel, making it more versatile for street applications. Before the fuel injection trials, this potent mill was delivering an impressive 860 horsepower when paired with a Sniper manifold from Pro-Filer Performance Products. The camshaft specifications were also on the more aggressive side, indicating a focus on high-end power output.

The Objective: Streetability and R&D

The overarching goal for this particular engine build was to dial back the extreme horsepower to create a more street-friendly combination. During this process, Prestige Motorsports saw an opportunity to conduct some crucial research and development. As Prestige’s engine builder and dyno operator, known affectionately as 'Senior', explained, "We wanted to see how some of Holley’s fuel injection systems worked on a motor of this nature." This desire to understand the real-world performance of Holley's EFI systems on a high-output engine formed the basis of the testing.

Baseline Performance: Dominator Carburetor

To establish a benchmark, the existing Sniper manifold was removed. In its place, Holley's single-plane intake manifold, designed for their multi-port injection system, was installed. The initial round of testing involved the use of a Holley Dominator carburetor, rated at 1150 cfm. A two-inch spacer plate was employed to adapt the Dominator's bolt pattern to the multi-port injection manifold. This carbureted setup yielded baseline numbers of nearly 840 horsepower, providing a solid point of comparison for the subsequent fuel injection tests.

Test 1: Holley Terminator Throttle Body Injection (TBI)

The next step in the evaluation was to swap the Dominator carburetor for Holley's Terminator throttle-body injection (TBI) system. This TBI unit was equipped with a set of 200 lb-hr injectors, known for their ability to supply ample fuel for high-horsepower applications. For consistency and to maintain similar airflow characteristics, a two-inch spacer plate was also bolted onto the Terminator throttle body, mirroring the setup used with the Dominator.

Holley rates the Terminator system at 950 cfm and typically recommends it for engines up to 600 horsepower. The results from the dyno were, therefore, particularly impressive. Despite the system being outside its commonly recommended power range, the TBI unit managed to support the considerable power jump, almost matching the horsepower figures achieved with the much larger Dominator carburetor. Senior commented on the drivability, stating, "It idled and throttled great. The running of the motor was far better than the Dominator. We were just lacking 10 or 15 horsepower. It was a good test." This indicates that the Terminator TBI system, while perhaps at its limit, offered a significant improvement in engine running characteristics compared to the carburetor.

Test 2: Holley Multi-Point Injection (MPI)

Following the TBI testing, the Multi-point Injection (MPI) system was installed. The results from the MPI system were very close to those achieved with the TBI system. Senior noted a slight difference in the power delivery, explaining, "We lost a little bit of torque and gained a little bit of power. At this point I would have to say the difference is where we are interjecting the fuel into the air stream versus air velocity."

He further elaborated on the potential reasons for the subtle differences, drawing a comparison between the two systems: "The Terminator disperses fuel similar to an annular discharge booster. I think it atomizes fuel better at the point of delivery versus one shot at the end of the runner. Now it has all this time for it to atomize from the throttle blade through the intake runner. The multi-port is shooting it in right at the flange; so you lose about 7-inches of travel there." This suggests that the TBI's placement of fuel dispersion may lead to slightly better atomization and a more homogeneous air-fuel mixture entering the intake runners.

Throttle Response: A Key Differentiator

One of the most significant findings from the comparison was the difference in throttle response. Senior highlighted that the Terminator TBI system exhibited more immediate and precise reactions to throttle input compared to the multi-port system. "It’s definitely more responsive," he stated. "I loaded the same program into both systems. We used the same fuel map and parameters for both, and it was night and day on the throttle." This difference in responsiveness can be attributed to the direct fuel delivery at the throttle body in the TBI system, potentially leading to a crisper feel for the driver, especially during acceleration.

Future Plans: Nitrous and Street Tuning

With a clearer understanding of the capabilities of Holley's fuel injection systems on an 800-plus horsepower engine, Prestige Motorsports is now moving forward with the planned transformation of the engine into a more street-friendly configuration. The next steps involve a camshaft swap and changes to the valve springs to better suit a milder performance profile. Following these modifications, the multi-point system will be re-installed and specifically tuned to handle a nitrous oxide system. Enthusiasts can anticipate exciting dyno videos documenting these future developments on Prestige Motorsports’ Facebook page.

Comparison Table: Carburetor vs. TBI vs. MPI

To summarise the key performance aspects, here's a look at how the different fuel delivery methods stacked up:

Frequently Asked Questions

Does Holley offer complete fuel injection kits?

Yes, Holley offers a variety of complete fuel injection systems, including their popular Sniper EFI kits, which are designed for ease of installation and tuning for a wide range of applications, from street rods to muscle cars.

What are the advantages of EFI over carburetors?

Electronic Fuel Injection (EFI) generally offers advantages such as improved fuel economy, better throttle response, more consistent performance in varying conditions (temperature, altitude), easier starting, and the ability to fine-tune engine parameters through software for optimal power and drivability.

Is Holley's Terminator TBI suitable for my high-horsepower engine?

As demonstrated by Prestige Motorsports, the Terminator TBI can support significant horsepower levels, even exceeding its rated capacity. However, for optimal performance and longevity on very high-output engines, Holley may offer higher-capacity TBI units or recommend their multi-port injection systems.

What is the difference between TBI and Multi-Point Injection?

Throttle Body Injection (TBI) delivers fuel through injectors located in a throttle body assembly, similar in concept to a carburetor. Multi-Point Injection (MPI), also known as Port Injection, delivers fuel through individual injectors placed in the intake manifold runners, directly before the intake valve. MPI systems often provide more precise fuel control and better atomization.

Conclusion: Holley's EFI is a Viable Option

The testing conducted by Prestige Motorsports clearly demonstrates that Holley's fuel injection systems are a capable and viable alternative to traditional carburetors, even for high-horsepower applications. While the Dominator carburetor provided strong baseline numbers, both the Terminator TBI and the Multi-point Injection systems performed admirably, offering improved drivability and throttle response. The choice between TBI and MPI may come down to specific performance goals, desired throttle feel, and installation considerations. For enthusiasts looking to upgrade their classic or performance vehicle to modern fuel injection, Holley provides compelling options with proven performance capabilities.

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