What boost psi requires an intercooler
 

Read somewhere that said 8 psi and under wouldn't benefit much from an intercooler. Is this rule of thumb?

Someone feel free to chime in and correct me if I'm wrong, but you pretty much always want a n intercooler. It's less boost levels but intake temps that have more to do with the equation. Turbos get very hot so intake temps rise well above ambient temps that an NA car would experience, which hurts fuel atomization. This is why intercoolers exist. Obviously for more boost you want to respond with a larger and/or more efficient intercoolers, but running without pretty much means you're not seeing the full potential of the turbo system.



There are alternatives like meth injection, but they're a lot more expensive than a small intercooler like 8psi would command.

If you're running real low boost levels (2-6 psi), then its fine to go without an IC. It's not recommended, but you can do it. However, why anyone would want to run really low levels of boost is beyond me, unless it's an S/C setup where the most you can get out of a smaller pulley is 2-8 psi anyway. :dunno:

just get an intercooler. they're cheap and effective