Originally Posted by markdunlap
If you have the mufflers up front just behind the header collectors, you may be able to install the evac tube in the piping behind the muffler and still use a vacupan system.
The venturi slot has to be placed right in front of the primary tubes to get a strong enough blast to create any vacuum so putting them behind the can is not a good idea. Usually the machining on the piece that gets welded in the header is pretty crude and you can enhance the efficiency of the slot with a file.