not necessarily true.
Wastegates are becoming increasingly popular in the centrifugal supercharger circles as a means of pressure control. For obvious reasons they are not used on the exhaust, but are instead installed on the charge tubes and utilized to prevent pressurization above a set point.
As is well known, supercharger "boost" is typically controlled by varying pulley size for a particular "peak boost." The other obvious, but often less noted fact is that a change in pulley size also effects the extent of "boost" production across the rpm band. Wastegates are being utilized to extend a specific "boost" level when coupled with a new pulley instead of increasing peak.
Example:
A hypothetical supercharger utilizes a pulley to produce 10 psi on an engine @ 5,500 rpm and 5 psi @ 4,000 rpm
A pulley change results in 20 psi @ 5,500 rpm and 10 psi @ 4,000
A wastegate setup to release at 10 psi is utilized with the pulley change. The engine now receives 10 psi from 4,000 - 5,500 rpm.
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