In many cases, aftermarket dump pipe inlet flanges don't properly align with the outlet of the turbine housing, as they were designed to fit within the constraints of a 3-inch pipe. When an oversized wastegate flapper valve is installed, it can interfere with the dump pipe flange. A bit of die-grinding usually resolves this issue. Additionally, the actuator must be preloaded, otherwise, the flapper valve may rattle. The stock wastegate also tends to open too early, so upgrading to a wastegate actuator with a stiffer spring can improve boost response.
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