The Invidia Evolution 9 cat deletes are 3in tubular 304 stainless steel with thick flanges to prevent warping. The Invidia test pipes can be used with the stock downpipe and cat-back exhaust or with most aftermarket components. The Evolution 9 test pipe has no bungs in it since the O2 sensor is located in the downpipe. The 06 Evolution 9 test pipe has an O2 bung to mimic the stock cat's location.
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