Before you install your exhaust system make sure all the pipes bolt together
without any one fitting off center.  On my exhaust the elbow did not fit
centered.  I had to grind about a quater inch of material out to remove the
restriction.  Check by using the exhaust gasket as a template.  Doing this
work removes restrictions to the exhaust and give you a little free HP and
stock WBX's need it...

Robert