Originally posted by Auto-X Fil: First off, flow is turbulent pretty much everywhere in the intake. There's no laminar flow in a system like this. It's pressure and velocity changes that designers try to minimize. Ideally the air wouldn't have to make a bend like it does, but it's far more important to get the length right. Packaging then dictates that it have bends. Variable intakes are now a pretty common thing on more potent engines, but it was fairly new, and quite an impressive feature on the original engine. Exhaust and intake both work best when they are long and small diameter at low revs, and short and wider at high revs. This intake, as you can see from the tubular pictures, delivers air through narrower, long tubes until the secondaries open, then through both them and the slightly wider, much shorter secondary feeds. Without the secondary design, the engine would just die at low revs. Imagine if the torque curve at 4k continued all the way down, without that hump... it would be pretty lousy at low revs, like most engines of this displacement.
Actually, your part about turbulent air in the manifold is not correct in all cases I'll wager. Laminar flow can occur in any shaped pipe or trough or whatever, even a rough surfaced one. The flow in the middle will be highest and then velocity will drop off as it gets closer to the walls. This indicates that the fluid nearest the walls doesn't even move and forms a static monolayer against the wall surface. It is the velocity that makes the flow transition to turbulent. So there are two main factors, velocity and surface roughness (shape) that affect when and how laminar flow transitions to turbulent.
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