to see if the wastegates are able to extend their full range of motion. I had over boost this last time I put my engine back in and when I did this test I found the passenger side actuator was not working at all! I had tested them and synced them before dropping it in. Turns out My brother in law had managed to get the wastegate hose pinched between the turbo outlet pipe and a coupler clamp when he wrapped the clamps around the couplers.