WARNING: this read could cause loss of sleep!!! 
http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf
Sparky,
This is the same link referenced by roygoodwin a couple of pages back. And yes, there is probably a bhp or 2 in "the best" inlet air horn. The problem is: Where do you get them? A LOT of the add on, aftermarket bits for carbs that I have flow tested, DO NOT JUSTIFY THEIR COST. I normally don't do this, BUT, I'll "decode" my last sentence: MOST of the stuff you buy, adds neither flow or bhp!! Reference my post #2617 on page 175 of MM's build diary. The trick, pretty looking, anodized, fully radiused, EXPENSIVE, aftermarket inlet bell LOST airflow on every comparison test!! It flowed less air than the STOCK Weber part!! Caveat Emptor! Many times a great idea on paper, gets compromised somewhere in the manufacturing process. Manufacturers claim all sorts of things, I want to see data for my (or my client's) application.
So having pontificated, I will also point out, I have NOT flow tested EVERY inlet bell for Webers. I am certain that there are some out there that are manufactured in a way so as to improve airflow over the stock part(s). I just don't have any numbers, YET. Interestingly enough, I'm going to be flow testing more 45DCOE's & 48DCOE's this week. I will be able to test about 5/6 air horns from 2/3 manufacturers, back to back to back. I'll post up the numbers later.
Someone with access to more machinery than I have, could certainly take Dr. Blair's formula and manufacture special bells for their application. I just don't want to be in the business of manufacturing anything anymore.
On an interconnected side note, the racers who loaned me the "trick" bells for testing were convinced that those parts would "far outperform the stock Weber parts". They also dyno test their engines and parts, but they don't flow anything, because their dyno guy doesn't think it's necessary . . . . . . because he feels the "dyno will point the way to go". He doesn't have a flowbench. I find it interesting that their "dyno development program" has stalled out @ 140/141 bhp (from 1310cc's) over the last 3 years or so, the time period that they have been using the "trick" bells. I'm modifying and flow testing 2 carbs for them. I'll post up those numbers and their bhp numbers when I learn them.

Dynoboy AND Airflowboy
(sheesh, which costume do I wear today Alfred?)
