Originally Posted by Boosted Performance

To add to the above statements....the open dump gates will be loud...very loud at WOT. If you stay out of boost there is no noise at all because the wastegates are closed. It get's loud as you approach boost spring pressure, and during WOT runs.

The turbo would spool just a tad quicker because a lot of the exhaust is diverted to atmosphere through the wastegates. It does not need to flow to the back with the exhaust that goes through/out the turbine.