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Carburetor vs Fuel Injection On Holley's New Hi-Ram Manifold

We test Carbs Vs. Fuel Injection On Holley's New Hi-Ram Manifold

By Richard Holdener, Photography by Richard Holdener

Carburetor vs Fuel Injection: Which are better, carbs or computers? Obviously, the Big Three have long since made the switch to electronic fuel injection to improve fuel economy, driveability, and lower emissions, but what about power? Can carburetors still compete with modern fuel injection when it comes to power production at wide-open throttle? The answer to this question came from Holley, thanks to its new Hi-Ram intake manifold designed for rectangular-port LS3 applications. The top of the Hi-Ram is interchangeable, and Holley offers both a throttle-body and dual-carburetor flange. For maximum-effort applications, the Hi-Ram can also be configured to accept a pair of Dominators, but we figured the 1,500-plus cfm offered by the 4150s was sufficient for our stroker LS3.

To properly test the merits of such an impressive induction system, we went big on our test motor. The original aluminum 5.7L LS6 block was sleeved using a Darton MID (modular integrated deck) kit, allowing us to bore it to 4.185 inches. We then added a 4.250-inch Lunati crank, K1 rods, and Wiseco pistons for 468 inches. The heads are dedicated castings from Procomp Electronics. The cam is a hydraulic roller from Comp with 255/271 duration at 0.050, 0.624 lift and a 115 LSA. The combination of flat-top pistons, Cometic MLS head gaskets, and 70cc combustion chambers produce a static compression ratio of a little more than 12.0:1.

Testing the new Hi-Ram in injected and carbureted form was as simple as swapping tops. First on the dyno was the EFI configuration, consisting of the upper intake, a 102mm throttle-body, and 50-pound injectors. The multiple mounting positions for the supplied fuel rail allowed use of different-length early and late LS injectors. The fuel rail was fed by an Aeromotive A1000 fuel pump while the timing and fuel were controlled by a Holley Dominator EFI system. Additional mods to the test motor included a Milodon oiling system, Lucas 5W-30 synthetic oil, and a set of 17?8-inch American Racing Headers. After dialing in the air/fuel and timing curves, the injected 468 produced 713 hp at 6,900 rpm and 614 lb-ft of torque at 5,100 rpm. Torque production exceeded 600 lb-ft from 4,500 rpm to 5,900 rpm.

Swapping over to the dual-quad setup required only an upper intake swap. The new top was configured with a set of 750 HP carburetors and jetted to optimize the air/fuel mixture. The ignition timing remained the same, as the Holley EFI was still in control of the timing curve. Thanks primarily to the charge cooling that comes from the introduction of the fuel at the top of the intake manifold, the dual-quads increased the power output to 724 hp at 6,900 rpm and 631 lb-ft at 5,300 rpm. The Carburetor vs Fuel Injection test illustrates that carb owners can stand tall, but no matter which one you choose, the Holley Hi-Ram is one serious induction system.

Power Numbers: Holley Hi-Ram - Carburetor vs Fuel Injection

Is fuel injection really the hot setup? When it comes to power production, the results of our Carburetor vs Fuel Injection test indicate that simple carburetion can more than hold its own against modern fuel injection. The versatility of Holley's Hi-Ram intake allowed us to directly compare EFI and a single, 102mm throttle-body against a pair of Holley 750 HP carburetors. The key to this back-to-back test was the two-piece Hi-Ram intake, which is designed to accept a number of different upper manifolds. For our test, we chose to compare the single-throttle-body EFI to a dual-quad upper intake. As indicated by the power numbers, the pair of carburetors not only offered more power but also improved the power output through most of the rev range. Credit for the majority of the power goes to the intake-charge cooling offered by the carburetion.

By Richard Holdener
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1 comments
FOUROHSICKS
FOUROHSICKS

Why not compare twin throttle bodies in place of the single throttle body upper,which is more of a forced induction set up? 

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