Manifold Destiny

Running The Numbers
As much as we enjoy debating theory around the office, it's the hard numbers that back up our rap. To get to the facts, we gathered some of Edelbrock's best single- and dual-plane four-barrel manifolds for the small-block Chevrolet and hauled them to the Westech dyno shop to get real empirical data. Testing was conducted on a typical hot-street small-block combination, a 0.030-over 350 displacing of 355 ci. Inside was a mild COMP street-roller camshaft, and topping the mill was a set of Air Flow Research 190 cylinder heads. This engine provides enough induction draw to produce serious power, while taxing the ability of an intake manifold to keep pace. Here's our take on what we found, and the numbers we recorded.

Performer
The standard Edelbrock Performer is a conventional two-plane divided-plenum performance manifold--a very popular performance upgrade on milder applications. Edelbrock markets and has certified this intake as an E.O.-legal stock-replacement item for many applications. Despite the stock replacement tag, the Performer was designed, as its name implies, as a performance upgrade over the OE intake manifold.

We used the Performer as our baseline intake, and were somewhat surprised to find that even on our stout 350, this intake offered credible output. The relatively low manifold height makes it an attractive alternative to stock in applications where hood clearance is an issue.

Performer RPM
The Performer RPM was a milestone design in two-plane intakes, created with the intention of providing the low-end performance benefit of a dual-plane, with the top-end performance attributes of a single-plane at higher engine speeds. To this end, the manifold height was increased, allowing the traditionally poor lower plane runners of the intake to provide a more direct path into the cylinder head port. The runners are branched close to the plenum and are laid over in a gradual curve rather than the log-style branches and abrupt angular pathway found in OE or earlier aftermarket manifolds.

In output, the RPM closely followed the power curve developed by the standard Performer, but by 5,500 rpm, the difference became apparent. Higher in the rev range, the RPM showed a clear advantage. The Performer RPM is about 0.7-inch taller than the standard Performer intake, so hood clearance needs to be considered.

Performer RPM AirGap
The AirGap was the next evolution in the Performer series of dual-plane intakes, characterized by divorcing the runners from the rest of the intake manifold. This design feature isolates the runners from heat gain via the tappet valley of the engine and allows the surrounding air to keep the runners cooler. Cooler runners allow for a denser mixture charge, which in turn promises improved output.

We never run out of good things to say about the AirGap intake. This manifold provides the torque advantage inherent in a two-plane configuration, while consistently providing top-end power rivaling a single-plane right to the top of its rated rpm range. In an engine application running up to 6,500 rpm, there is little if anything that will touch the AirGap in output. The AirGap provided by far the strongest average output numbers in our tests.

Victor Jr.
The Victor Jr. was the first of our single-plane entries. Long regarded as the single-plane intake of choice for a variety of race and hot-street applications, the Victor Jr. is a very versatile manifold. With a moderate runner and plenum volume, the Jr. is responsive, while providing power comparable to some race-style intakes in street/strip or moderate race use.

True to form, the Victor Jr. made more outright peak horsepower than the dual-plane intakes, but as compared to the AirGap, not by a large margin on our test engine. Closer scrutiny, however, shows that the averages were down in comparison to the dual-plane intakes. In a racier engine combination at a much higher rpm, the single-plane would likely be more in its element, but even in the range of our test, the enhanced power production up top was clearly shown.

Super Victor
The Super Victor is a true race intake manifold designed for high-rpm output in racing applications. This manifold is substantially taller than the Victor Jr., providing for a more advantageous approach to the cylinder-head ports. The Super Victor is large, not only in terms of height, but also in runner cross-sectional area and plenum volume. Notice the runner entry--extending deep in the plenum, looking to grab a world of air. The extended runners lengthen the apparent runner-length and boosts torque and carb booster signal in this high-volume manifold design.

Being more of a race unit, this manifold wouldn't represent the obvious choice for an engine configuration as tested, but we deemed it worthy. The Super Victor provided an unexpected improvement in average torque compared to the Victor Jr., and tied the Victor Jr. for top output honors on this high-powered small-block combo.

Multi-Carb-Allure
Since the early days of hot rodding, modified performance engines have been adorned with all manner of multi-carb arrangements. In the early days, it was Flatties with strings of Strombergs. Later, even the OEMs took up the action, with Chevy 283 small-blocks rolling off the assembly line carrying matched WCFB's, or Pontiac mid-blocks sporting a trio of Rochester 2G's. In the early days, it was a matter of necessity because capacity was a lacking ingredient in the antiquated carb designs of the day. Even as the first four-barrels appeared, their flow capacity was meager in comparison to today's mixers. Multi-carb arrangements came forth as a way to address the short supply of available cfm in search of higher output.

In your face with a trio of... 

   

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In your face with a trio of high-capacity 2300-series Holleys on a high-rise dual-plane, the famous Mopar Six-Pack can be tuned to deliver comparable performance to today's best street four-barrels, with the bonus of gas-guzzling good looks.

Today, the range of available four-barrel carbs can handily supply all but the mightiest race engines. Indeed, there are some applications where such exotica as split-Dominators and sheet-metal intakes prevail. In these instances, the drive toward multi-carbs is motivated by requirements of manifold design, fuel and air distribution needs, as well as ultimate flow capacity. Even outside the fraternity of extreme racing, interest in multiple carbs persists. Taking a cue from the past, for many enthusiasts, the mystique of multiple carbs is reason enough--purely visual. In some instances, multi-carb arrangements can be just as functional as they are attractive and traditional. Multi-carb arrangements can be found in virtually any configuration the mind can conjure. Some are notoriously problematic, while others have proven quite effective, even compared to today's highly refined four-barrel systems. While logic dictates that a single four can meet any street engine's requirements, emotions ensure that multi-carbs are here to stay.