Here'* why an intercooler won't work on NA engine.
There are 2 typical types of intercoolers:
air to air: after the intake air is compressed (which creates heat) it is routed through a radiator core that has ambiant temp air rushing through the vanes, taking heat from the intake air with it. In a perfect air to air intercooler, your intake air will be ambiant temp when it exits, but obviously it'* not perfect.
air to water: after the intake air is compressed it is routed through a radiator core that has coolant or some other fluid rushing through the vanes, taking heat from the intake air with it. The fluid then goes through another radiator core where it dumps heat into ambaint temp air... a lot like air to air, but there is a middle man.
In an NA engine, your intake air is already ambiant temp. Now, you can increase an intercooler'* efficiancy by spraying the core with cold water or something along those lines, which would be necessary for an NA engine to cool the intake air more than it already is.