The 9.6:1 compression 463-cube...
The 9.6:1 compression 463-cube test engine, shown here back in owner Bill Wise's '74 LeMans, features a 252/256-degrees duration at 0.050 solid roller cam with 0.578/0.540 net lift and a 112-degree LSA, a Torker II intake, 6X heads that flow 255/180 cfm, and 1.75-inch headers.
The definition needs to be altered slightly when discussing an intake manifold. During part throttle operation, the plenum is under a vacuum, and at WOT it's near atmospheric pressure. The purpose of the plenum is to allow for distribution of the charge to the individual runners and depending on the intake manifold and engine design, allow the pumping action of other cylinders to impact the fill rate on the companion bores.
The carburetor is attached to the plenum, and the capacity has a direct impact on idle stability. As the plenum volume increases, in most cases so does idle instability. Being application specific, a general OE consensus is the plenum volume should be approximately 1.5 times the displacement of the engine. As an example, a corporate LS1 has a plenum volume of 10.1 liters or 1.77 times the displacement of the engine. To be considered a plenum, the chamber must be after the throttle plate and before the intake manifold runners.
Single Plane:
Most commonly found in performance applications with an open plenum, it's easily identified by its short, nearly equal-length runners. Intended for continual high engine-speed use, this design is less streetable than a dual-plane configuration. The large capacitance undivided plenum suffers from a weaker venturi signal to the carburetor. This is usually met with low speed fuel-metering inaccuracy. It's a function of exposing all of the cylinder's pumping pulses to the barrels of the carburetor. A benefit is the equal-runner-length, straight flow path, and consistency in fuel distribution allow for efficient operation at higher rpm, albeit with a trade-off of low-speed torque, driveability, and fuel economy.
As with any induction-system...
As with any induction-system modification, the intake manifold needs to be tested with the cylinder head for the most accurate data.
Dual Plane:
The most common manifold design, it lends itself to a street or street/strip style engine. It may look simple, but it's more complex than it first appears. To be classified as a dual-plane would require one of the following criteria to be met: The intake runners need to be divided into two distinct groups, actually taking an eight-cylinder engine and treating it as two four-cylinders. Each group then needs to alternately receive induction pulses with these pressure differentials being evenly spaced. Commonly equipped with a divided plenum, low-speed torque is enhanced. To be qualified for a dual-plane application, the firing order of the engine needs to be evenly spaced. Odd firing sequences (early Buick V-6 engines) will not benefit from the strengthened pressure waves during filling of the cylinders and are not well suited for this design.
Tunnel-Ram:
It could be thought of as the big brother to the single plane. Intended for high-rpm racing applications, it offers a significant advantage over a single-plane design by providing a large plenum that will support multiple carburetors. The runners are moved up off the valley of the engine, which allows for cooler charge air temperature. The short, straight runners also offer less frictional flow loss. Falling pray to hood clearance concerns, its real benefit is the ability to attach multiple carburetors. This will limit the pumping losses of the engine. Today, there are tunnel-ram designs that use only one carburetor. In most instances they are not as efficient as a good single plane except at very high engine rpm.
Sheetmetal:
The all-out racing sheetmetal intake allows for complete freedom of design. An attribute of this material is the very smooth internal surface limiting frictional flow losses. Cost being relative, a good sheetmetal manifold may set you back $3,500 or more.