Running The Numbers
Talking theory makes for good conversation at the club, but analyzing hard numbers is the best way we know to get to the facts. To this end, we assembled a collection of Edelbrock's intake manifold offerings for the small-block Chevrolet, and took the trip out to Westech's dyno facility to run them for the numbers. Our test engine is a typical hot-street small-block, with a displacement of 355 cubic inches and a mild Comp street roller camshaft. Topping the mill is a set of Air Flow Research 190 cylinder heads, providing enough induction draw to produce serious power, while taxing the ability of an intake manifold to keep pace. Here is how they stacked up.
The standard Edelbrock Performer is a conventional dual-plane divided-plenum performance manifold, and a popular performance upgrade in milder applications. Edelbrock markets and has certified this intake as a 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 manifolds.
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.
The Performer RPM was a milestone design in dual-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 laid over in a form akin to a gradual curve rather than the traditional 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, and, like all the high-rise intakes tested, represents a hood clearance problem in most Corvette applications with stock flat hoods.
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 dual-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.