The bigger the tube, the slower that same volume of air will have to move through the tube, and the slower the air, the lower the restriction will be through that tube.Originally Posted by f3racer
Show your work
3" Diameter x 10" tube:
Volume = pi * radius^2 * height
Volume = 3.14 * 1.5^2 * 10
Volume = 3.14 * 2.25 * 10
Volume = 3.14 * 22.5
Volume = 70.65 in^3
4" Diameter x 10" tube:
Volume = pi * radius^2 * height
Volume = 3.14 * 2^2 * 10
Volume = 3.14 * 4 * 10
Volume = 3.14 * 40
Volume = 125.6 in^3
Difference: 77.78% increase in volume from 3" to 4" tube.
The longer the tube, the more air is restricted. This is something that, alone, I suspect would make a noticeable difference only with an exceptional length, such as more than three feet. It's something like a 3% increase in restriction per foot.
Bends add a considerable amount of restriction, though. A 90* bend (or two 45* bends) would be somewhere along the lines of a 17% increase in restriction in a 4 inch tube.
So a 4" x 10" tube with a 90* bend is still ~5% (or shall we say, negligibly) less restrictive than a straight 3" x 10" tube with no bends.
