Intercoolers reduce the heated compressed air from a turbo, as you probably know. However, if you keep your engine N/A, the air inside the intercooler is the same temp as the air outside (since it has not been compressed), and no cooling occurs. Thus, an intercooler on a naturally-aspirated car does no good, and in fact, hurts performance, due to the fact that the longer and more restrictive path the air has to take on it's way into the engine increases pumping losses and hurts throttle response.