as far as why is the outlet bigger than the inlet...its a common practice with intercoolers. check out the stock TMIC, 2.25 in and 2.75 out I think (close to that anyways). it's smaller on the hotside to get the air to the intercooler quickly and reduce lag. Once its past the IC, its about having the least amount of restriction to the throttle body. With intercoolers a lot of the design has to do with pressures, not just velocity like in exhaust design.