Okay, here is an engineering theory perspective. (There, that should stop 80% of the readers so they can continue to the next post.)
Velocity stacks provide at least two benefits.
1 - They keep the airflow laminar and reduce turbulence eddies than can alter the pressure at the fuel exit points in the carb throat.
2 - The ramming effect at high air speeds, provides a bit of compression on the air mass (large cross section narrowing to small cross section), which makes more oxygen available during combustion. A slight supercharging effect.
Air filters of any type, introduce turbulence as the air passes through it. Placing it at the entrance of the V stack largely negates benefit number one.
Filter media at the bell mouth actually reduces the cross sectional area of the bell, thereby negating benefit number two.
Passing large amounts of air through a small restriction increases the pressure differential on either side of the restriction. With the pressure differential, comes resistance in the form of drag on the air mass. To reduce the drag effect from the air filter, the media should be as large as possible and many times the cross sectional area of the carb throat. The tiny holes in the filter media don't flow as well as a large one, because of circumferential boundary layer drag effects. However, providing millions of small holes, allows each to flow at very slow rate. This is rather the equivalent of have one person lift 300 lbs. or 100 persons lifting 3 lbs. each.
At the risk of sounding like a stock purist, which I am not. I will point out some features often over looked on the SOHC4. Using the CB550 for example, you will find a large chamber where air enters and is met with a large surface area filter. This area is far larger than the venturi cross sectional area of the carbs. After filtration, the air moves to a plenum chamber with exits to the 4 carbs, Each, plenum to carb coupler is formed out of rubber in the shape of...
a short velocity stack. This stack is really too short to provide much compression effect of number two benefit above. But, it does provide some laminar flow benefits of number one.
You may not like the stock arrangement looks. But, you can't deny that Honda got the engineering right, a large filter before the carb entrance and flow straighteners at the carb entrance.
Honda was trying to offer best performance with engine longevity. This is a trade off proposition. Racers trade off longevity with power gains for the short haul. Because they go fast, racer bikes have the eye allure. If you have a racers budget to replace engines or engine components, use velocity stacks.
One last point about the filter-at-the-vstack bell. As filters block dirt, they become more restrictive. A small area filter will need more frequent maintenance than a large area filter flowing the the same volume of air, because blocking the particles further restrict air flow. This will, of course, depend on an equivalent air particulate density provided to each filter type, large area or small.
Having said all that. I will support what Fred Said.
You build it........they will come!!!!!!!!!!
Since there are so few real engineers in the bike building arena, the cool factor is what will sell. Just don't provide any test data. Show them a cool bike with your shiny stacks gleaming in prominence. (Polished aluminum on an all flat black cafe bike, for example.) With proper photography, you'll sell a bunch of them.
Cheers,
P.S. I wish I had your solid modeling skills!
