One with the farce
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Okay, an intake manifold can be single plane or dual plane, and I'll just paste a bit of info here, maybe skim through it and see if it makes sense.
Single-Plane Versus Dual-Plane
A single-plane intake manifold is the simpler of the two layouts, connecting the plenum under the carburetor with runners leading fairly directly to the cylinder head ports. The two-plane design appears more convoluted with a divided plenum with one side's plenum dropping down lower than the other, and the respective high or low runners routed alternately to the left and right cylinder heads of the engine. Most any motorhead can distinguish a single-plane intake from a two-plane just by looking at it, however, surprisingly, few know what the difference is conceptually. Let's take a look at dual-planes first.Though many early OEM engines used single-plane manifolds, auto manufacturers overwhelmingly favor the two-plane design. Looking at a two-plane, with some runners crossing over from side to side, a two-level divided plenum, and the obviously greater complexity in casting such a piece, we have to ask why the manufactures would go through the trouble. A single-plane open-plenum intake would obviously be easier to design and cheaper to build. Why bother with a two-plane? The design has many advantages.
As a general rule, it has been found that a two-plane intake improves low-rpm response, torque production and idle quality. These are pretty worthwhile characteristics, so it's worth exploring why this is the case. Runner length plays an important part in the rpm range at which an induction system "tunes-in," taking advantage of the natural pressure wave pulses in the intake tract to provide a greater charge density in the cylinder, and therefore more torque and horsepower. As a general rule, longer runners "tune" at a lower rpm range, while shorter runners favor the upper end of the rpm band. Similarly, it has been found that a smaller plenum also favors power production lower in the rpm range, while larger plenums are more inclined to boost the top-end. In these two characteristics, the dual-plane has natural advantages over the single-plane, but there is more. Runner cross-sectional area also plays a part. Smaller runners necessarily result in higher air-stream velocity in the manifold, which improves cylinder filling by improving inertia effect by virtue of the energy contained in the moving gasses. A dual-plane design generally features runners of a smaller average cross-sectional area than a single-plane, lending itself to higher velocity at low rpm.
All of these characteristics provide a low-speed advantage in their own right, but the effects are compounded when the carburetor is considered. Taken as a group, a smaller cross section, longer runners, and a smaller plenum create a system that is more responsive at transmitting the induction signal from the cylinder to the carburetor booster. This improvement in signal by the air stream connecting the cylinder to the carburetor improves the carburetor's metering response, and aids in low-speed atomization.