Dyno Comparison of Holley TBI and MPI systems on 800 HP Big Block

Holley has many options in the fuel supply realm. Prestige Motorsports recently spent some time on their in-house engine dyno to find out how well two fuel injection systems supported an 800-plus horsepower neck-jerker. While overall air flow was somewhat restricted compared to a large Dominator carburetor, the 4150 style throttle bodies did well on such a large displacement engine.

The base engine was Prestige Motorsports’ 582 cubic-inch big-block Chevy. Sealing off the deck is a set of Edelbrock CNC-ported cylinder heads.  Compression rolled out to around 10:1, which allows them to use premium pump fuel. Prior to this set of tests, the engine was running 860 horsepower with a Sniper manifold from Pro-Filer Performance Products. The camshaft is also on the aggressive side.

The end goal for the engine is to knock the power level down for a more street-friendly combination. In the process of doing that, Prestige took the opportunity to do some research and development. Prestige’s engine builder and dyno operator, known as Senior, explains, “We wanted to see how some of Holley’s fuel injection systems worked on a motor of this nature.”

Holley's MPI system. The 4150 style manifold from this kit was used for the tests.

Holley’s MPI system. The 4150 style manifold from this kit was used for the tests.

To start, the Sniper manifold was removed and Holley’s single-plane intake manifold from the multi-port injection system was installed. First round testing for this combination was completed using an 1150 cfm Holley Dominator carburetor. A two-inch spacer plate was installed to adapt the Dominator’s bolt pattern to the multi-port injection manifold. Baseline numbers reached nearly 840 horsepower.

Next, Prestige swapped out the Dominator for Holley’s Terminator throttle-body injection (TBI) system. The throttle-body was equipped with a set of 200 lb-hr injectors, and bolted on its own two-inch spacer plate for consistency.

Holley rates the Terminator system at 950 cfm and recommends the system on engines up to 600 horsepower. Impressively enough, the TBI system was able to support the considerable power jump, almost matching the horsepower of the Dominator.

“It idled and throttled great,” says Senior. “The running of the motor was far better than the Dominator. We were just lacking 10 or 15 horsepower. It was a good test.”

Throttle Body Injection Testing Video

 

Finally the Multi-point injection (MPI) system was installed. Results were very close to the TBI system.

“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,” explains Senior.

(Left) Holley's Terminator TBI. Special-order 200 lb-hr injectors were installed to feed the 582 BBC. (Right) The patent pending fuel ring disperses fuel similar to an annular booster.

“The Terminator disperses fuel similar to an annular discharge booster,” he continued. “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.”

Senior pointed out that the Terminator was more responsive to throttle input than the multi-port system.

“It’s definitely more responsive,” he states. “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.”

Torque and horsepower comparisons of the Terminator and Multi-port systems.

Now that Prestige has a good idea of the capability of the Holley systems on an 800 horsepower monster, it’s time to continue the transformation into a street-friendly version. A camshaft swap and valve spring change are up next. Then the multi-point system will be re-installed and set up to spray nitrous. There are sure to be some cool dyno videos to follow on Prestige Motorsports’ Facebook page.

MPI Testing Video

About the author

Eric Labore

Eric LaBore's extensive background includes a solid education in automotive and high performance motorsports technology and 10 years of working in the industry. Currently, he is a full-time ASE master technician and advanced engine performance specialist. As a former dyno operator and engine assembler, he is passionate about custom and performance engines.
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