At what boost level will I need to install an intercooler?
It is generally accepted that you can run 5 or 6 psi without an intercooler. Keep in mind that it'll be safer if you use an intercooler even at low boost levels. The cooler air coming into the engine can yield more peak power as well, so it's a good idea all around. Most junkyard intercoolers will work just fine, but if you're planning on squeezing some major power out of your turbo, it'd be best for you to get an intercooler that is built for racing applications. There are sources of cheap intercoolers out there, such as http://www.johnnyracecar.com/. There is almost no excuse not to put an intercooler on your setup. It could mean the difference between a great turbo kit, and a 2000 pound paperweight sitting in your driveway.
