A few more things to consider for this issue.
First, as Frank mentioned in his original post, multiple carburetor setups are NOT additive! Thus two 600 CFM carbs are a dual 4 setup do not equal 1200 CFM. This is why I suggest that one will obtain BEST results by using a multiple carb setup such that the number of barrels is an even divisor of the number of cylinders.
Next to consider (again from the original post) is the concept of progressive carburetors. Here there are some HUGE misconceptions. Most would suggest that progressive carburetors came about in 1952 with the introduction of the 4 barrel. However, progressive carburetion was available as early as 1903 (the Schebler model D) where 2 inputs were used on a single barrel carburetor. The first input (fixed) was tiny, allowing high velocity of air for decent (for 1903) carburetion at low RPM, and a secondary (spring tension controlled) input would open as needed for additional air (and fuel) at higher RPM. There are other methods of early progressive carburetors.
Fast forward to 1952. The 4 barrel carbs were progressive, having a primary and a secondary side. The huge misunderstanding is the way many view these as either mechanical or vacuum secondary. This definition omits the "on demand" secondary.
Let us define the types:
Vacuum secondary carburetors generally have a diaphragm, usually but not always in conjunction with a spring; that control, based on a vacuum signal when the secondary opens to WOT.
Mechanical secondary carburetors open to WOT when the operator mashes the throttle.
But, in my opinion, the most important class for street use, is the "on demand" secondary. Representative of this type would be the post-1960 Carter AFB with the weighted airvalve, or the Rochester Q-Jet and Carter TQ with the spring-tensioned airvalve. These units are designed to open ONLY to admit the amount of air that the engine can use; maybe NEVER actually opening to WOT. It is this class of carburetor which allow huge (in terms of WOT) carburetors to be used on smaller engines, because regardless of the pressure the operator places on the throttle, the carbs will only open as necessary for the engine demand.
Frank, you entered another issue in your second post; that of the sidedraft Webers.
Without getting into the mathematics (I had to edit my first post, as I initially divided by the square root of three rather than the square root of 2 - had a "senior" moment!) the equation from your first post is valid for a multiple cylinder 4 stroke engine of at least 4 cylinders fed by a common plenum area!
Most sidedraft Weber setups do not utilize a "common plenum area". The barrels (or carbs) are connected by a balance tube to minimize pulsing, but by and large each barrel feeds an individual cylinder. Single cylinder 4 stroke engines require TWICE the air as provided in the equation above. By not using the common plenum, the engine, for the purposes of carburetion, must be treated as a single cylinder engine.
Finally, engines are flexible, and many (most?) enthusiasts do not perform sufficient testing to determine if their combination is merely adequate, or highly tuned.
I always suggest that prior to any modification a "baseline" is determined. If your goal is increased acceleration, then run an acceleration test. Have a friend time you from zero to some fixed speed (not to exceed the posted limit) with a stop watch. Run three (or more) runs and average the times. Now make your modification and run the test again. You now will have actual proof of whether or not your modification actually improved your time.
If your goal is fuel economy, do a tuneup, drain the fuel system and introduce a fixed amount of fuel. Drive the vehicle at a fixed speed until the fuel runs out. Make the modification and redo the test. Again, you have real proof of the results.
Many enthusiasts love their aftermarket carburetor because they removed a worn original, possibly with a stuck power valve, or leaky float and replaced this unit with a new aftermarket unit. Generally, even the very worst of aftermarket carbs or one that is incorrectly sized is going to win in these circumstances.
Jon.
