[Andrew Bohan]

here's what corky bell has to say about ducting.

Originally Posted by Corky Bell

DUCTS. A duct is, in a large sense, form of streamlining of the core. The ducts present the air molecules with no alternative but to go on through the core. Do not underestimate the ability of a duct to improve the efficiency of the intercooler. I would suggest that an improvement of 20% is possible, good duct versus none. When constructing ducts, it is decidedly worth the extra effort to insure that the air molecules have no alternative but to go through the core. That is, seal all edges, corners, and joints.

It is not necessary for the duct inlet to be as big as the frontal area of the IC core. A rule of thumb is that the duct inlet should be at least one-fourth the core area. This rather strange situation is brough about by the fact that less than one-fourth of the air molecules would get though the core with little of no attention to ducting.