Modular: I know the "bracing" molded into the tube is not on the inside. I was talking about the bellows and kinks.
"Vacuum” is a relative term. In it's basic definition, it’s the absence of pressure - In this case, atmospheric pressure. The ideal method to test for intake restriction would be to check pressure differential with a manometer across various points in the system. Lacking that, a very high resolution vacuum gauge could be used to test for relative vacuum (decrease from atmospheric pressure) at various points in the intake tract. Any reading will be very minimal, which is why a manometer would provide a better indication.
There is no doubt that ANY type of filter element will create pressure differential. Oil bath filters create some PD. Even centrifugal "filters" used in some processes create a PD by causing the air to rapidly change direction. An elbow or bend in a duct, even though it might be the same size, and as smooth as possible, will create PD. Moreover, the ductwork itself, even at a fixed, constant size and with a mirror-smooth wall will create a PD along a sufficient length due to circumferential or perimeter surface friction and the induced laminar flow. At a shorter length, the restriction is less significant, but is still a restriction nonetheless. This involves fluid dynamic principals.
That said, there are practical limits and constraints in all applications, and a minimal PD has to be acceptable. For example:
*Even though a section of duct will create pressure drop, the loss over a relatively short length, like the three-foot long intake tract, is so minuscule it’s really not worth considering.
* Running without an air filter is unacceptable in the long term, so that is a necessary restriction. The design of the filter will affect just how much PD will be created. Using the largest possible element surface area is usually the best for reducing PD.
* Increasing the diameter of the duct in bends will eliminate the PD created by them (That's one of the reasons the factory uses plenum boxes in several areas of the intake tract on GM cars. The “problem” is created by the aftermarket "rocket scientists" who frequently don't have a thorough enough grasp of the science to know what they're looking at, and only see a restriction. That's not to say that the factory systems are perfect, but neither are the aftermarket systems.)
* Although flexible, bendable, or “accordion” tubing is frequently used to make connections, the effective size of such fittings should be calculated at something less than the smallest I.D., since those sections of duct will impart even more perimeter surface friction.
* The number of bends should also be considered, since every change of direction creates some PD in a system.
The process is probably not best defined as “adding power” as much as “reducing factory imposed restriction” created by a practical compromise between effectiveness, practicality of the installation, and cost.
I am not necessarily debating the usefulness of my intuition that the car may benefit from replacing the factory rubber bellows with a solid piece. We can talk all day about principles and theory, but I am just going to go and test it. If it doesnt work at all, I will be out about 100$ and that is a risk I am willing to take.
GM guys replace the factory rubber bellows all the time, and have dyno results to back up a gain, as well as mustang guys switching out to a K&N filter or a CAI. I understand everything is different, but to take an engineering blurb from a supercharger company and apply that one principle to anything in the intake system is not quite accurate. Principles of fluid dynamics are also in effect here, and aside from that a N/A engine behaves a bit differently than a forced induction engine.
I am not looking to pick up 50 HP here. I understand any gains are going to be small, but I do not want to leave anything on the table, and aftermarket CAI's are allowed in my racing class.