Turbochargers are essentially air compressors driven by exhaust gases. While some manufacturers will size the turbocharger's exhaust turbine so that it can never over-speed, this requires very precise calculations and data, as well as a turbocharger custom-made for a particular engine. The more universal solution is to install an exhaust bypass valve that opens when the boost pressure reaches a certain level. On any engine equipped with one, a properly-functioning Wastegate can make the difference between absolute power and total meltdown.
Install the adjustable pressure regulator into the air-line's quick-disconnect fitting, if your compressor doesn't already have one. Adjust the regulator to cut pressure at your turbo's maximum psi levels. If your car doesn't have a boost gauge installed in the cabin, then refer to a repair manual or an online resource to find the appropriate boost level.
Disconnect the Wastegate's boost sensor line from the intake tube or intake manifold, depending on the engine. Locations and types vary, but the boost sensor line usually attaches directly to the Wastegate on the turbo. Follow the line from the Wastegate to the intake and disconnect the line.
Install the air sprayer into the end of your air line and turn the compressor on to build pressure. Wait for the compressor to turn off, then firmly press the sprayer's rubber tip into the end of the boost line. Hit the trigger on the sprayer and watch the actuator rod on the Wastegate: It should immediately move when you apply compressed air.
Listen for sound of the Wastegate opening, if it doesn't use an external actuator rod. With the engine and compressor off, you might be able to hear it without assistance, but a stethoscope would help. If you don't happen to have medical supplies laying around, you can press the tip of a long screwdriver to the base of your turbo. Press your ear firmly to the screwdriver handle and the drivers' metal shaft will conduct the sound of the Wastegate directly to your ear.
Turn the regulator setting down by about 2 psi and re-test. An early-opening Wastegate is an indication of a worn-out Wastegate spring. A certain amount of movement at 2 psi below max is normal, but a Wastegate spring that allows the valve to open at 4 psi or lower is probably worn out and is costing you horsepower.
