Distance from Air Filter Above Carb to Carb Top??
No data handy to post. But what I have learn first hand.
More filter is better. More diameter is better. More pleats the better. Taller is better. (Seen from history) The ability to flow air straight down into the carb is better.
2-1/2 is a good a driver. This is a in general amount for driving down the road on the primary alone. More is better. Then again, it could be enough.
(Picked up elsewhere) Air doesn’t like to turn, it only turns so much so fast. More area above the carb makes turning the air easier as well as more available volume above it.
Mathematically working out the area of throttle bores to the available amount of element filtration doesn’t mean you have enough available air flow through the element or enough area to allow the carb to breath at it best. Air fuel ratios (via 02 meters on board) lean out with more filter. This is personal experience.
The 2-1/2 inch number is a general number that is reasonable for a simple driver to a in general hot rod build most often seen here. This number graduates higher as the power goes up.
On the above picture, when the fiberglass 6 pack hood was on the car, a taller filter was used. The switch had me lean out the carb and a noticeable throttle response change was noted. Small, but there and only under full throttle. Not driving around town or at medium speeds.
Also, a 4 inch high filter doesn’t have 4 inches of filter but just a little less. I also question just how many much of the filter itself is working & how well.
Since the question was general and not specific to the posters except engine specs or intended usage, a in general answer was given.
Rumble,
What makes you think 2 1/2" clearance is the minimum? Just wondering, do you have source/data that recommends this?
I do not see a problem in the pic in post #6, with a 1 1/2" gap. I spot a Carter/Edel AFB/AVS. The biggest size is 800 cfm with 1 3/4" t/bores, total area of 9.6 sq in. Using 8" as the smallest diameter of the A/C base where the 1 1/2" restriction occurs, I get 37.7 sq in of breathing area, 4 times the area of the bores so I don't see how a flow restriction could occur. Also, plenty of clearance above the carb vents.