[ivymike1031]

whether or not to use a CAI on a turbocharged setup is an interesting question.

Given the choice of taking your air from under the hood (hot) or from outside the engine compartment (cold), performance considerations will almost always push you towards the latter. Compressing cold air takes less energy than compressing hot air by the same ratio. This is the reason for using real* intercoolers, which go between the compressor stages on a turbine engine. Compressing cold air results in a cooler charge than compressing hot air, which may or may not be important, depending on the effectiveness of the intercooler. If the intercooler is already bringing the intake charge within a few degrees of ambient, then the charge won't get any cooler as a result of the CAI (but you could perhaps opt for a smaller intercooler). If the charge leaving the intercooler is considerably higher than ambient, then taking in the cold air initially will definitely help. So for the efficiency of the turbo, the cold air intake is always helpful. For charge temp & density, it's not always going to be important.

The other considerations in a design will occasionally outweigh performance. Packaging and cost are two big hitters, especially in the case of a retrofit. If the CAI costs too much to add, then forget it (I doubt that this will be the case). If a CAI cannot be packaged within the engine compartment in an aesthetically pleasing manner, or at all, then it might not be worth trying to stuff one in there. If the ducting is too complex or long, then a CAI might not work anyway (air will have time to heat up as it travels through the tubes). Most of the time it's a simple matter to duct your air in from outside the engine compartment, and the decision is simple ("just friggen do it!"). These sorts of points can be debated ad nauseum; I think the performance portion of this discussion is more pertinent.

*(the things on cars that are commonly called intercoolers are, in my opinion, more appropriately called aftercoolers. Some people count the compression stroke in the engine as a compressor stage, however, and thus justify the name "intercooler").