TwoTired, you're right about my statement:it's not really true. However, a carburetor/intake assembly is a control volume system and the volume of air is always the same, regardless of RPM.
Wait? What? How can that be? RPM is related to air speed, right? And, for any given orifice size, volume is a function of pressure differentials present at the inlet and outlet of that orifice. Since the inlet (or vacuum source) for the SOHC4 engine is pulsed, the average pressure depression is related to the spacing between those pulses. Surely, sustaining an engine operating at higher RPM requires more volume of air than at a lower RPM, won't you agree?
The throat pressures at the jet exit points are also affected by the venturi effect. (Bernouli's principle), which is certainly affected by air speed and volume.
What I've been able to come up with is that an unobstructed velocity stack enables air at atmospheric pressure to be more effectively (not necessarily efficiently) sucked into the carb. An air box/filter/sock/obstruction will cause a pressure drop between the atmosphere and the carb throat, which is what Honda designed for. By removing the pressure drop device the amount (mass flow) of air to the carb is increased. Am I right, or is there something I missed?
I think that's a fair grasp of the concept.
Also, a true velocity stack, also slightly compresses the air at very high velocities. Putting more oxygen into the carb throat/engine cylinder can make the engine produce more power.
As far as Laminar/Turbulent flow is concerned they're affected by a lot things. In a pipe the primary factors are surface roughness and velocity. However turbulent flow can be made laminar by using a flow straightener. google 'laminar fountain' for some examples of laminar flow at 'turbulent' velocities. A flow straightener is essentially a bunch of straws packed into a pipe, which simply encourages the fluid to flow in straight lines.
Agreed, I've seen these.
But laminar flow does not mean the air molecules are all traveling the same speed. The air molecules touching or right next to the tube wall are either not moving or moving much slower than the air near the center of the tube. It is a layered effect within the tube when viewed at a 90 degree axis to the air flow. At some increased speed, the friction between layers induces turbulence within the tube. The flow straighteners, therefore, have a speed limitation. To keep the speeds down within the "straightener tubes" the major diameter of the tube bundles must be increased, as anything you put in the air flow channel effectively reduces total cross sectional area AND adds more area/volume of stationary molecules in the air path.
As to the original topic; A lot of people buy velocity stacks because they look cool, the drawback is that you need to re-tune your carbs.
Very true, also because they saw a track racer with them on it. And it is a simple and cheap part to install.
A Velocity Stack with a built in pressure drop device would allow you to have the looks without the re-tune.
I'm not trying burst your bubble. But, I do have trouble seeing where putting anything but moving air within a velocity stack, will maintain velocity stack function. Yes, you can put a restrictor inside it, hidden from view, that may mimic the stock air box. But, won't it also displace air volume (and the performance boost oxygen it contains) above and beyond what the stock air induction arrangement offers?
So my question is:
Is the fundamental idea to purposely sacrifice engine capability for the benefit of stack looks without carb retuning?
Cheers,
P.S. Thanks for giving me an excuse not to go back out and work in the heat for a time.
