Exhausting

  Ok,  so I saved a few dollars by purchasing an OBX 4-2-1 header from Ebay.  Overall quality, finish, and welds are very good, but it does take some effort to get it installed.  The header will not physically fit into position unless the steering shaft is moved or the engine is pushed to the right.  Fortunately, I was installing Mazda Competition motor mounts at the same time so all I had to do was jack the engine up a few extra inches and the header slipped right in.  Then I wasted time trying to get the EGR tube to fit because the angle of the fitting is off a few degrees. Also, a slight misalignment in the header causes it to rub against the flange between the engine and transmission.  A new midpipe from Good-Win-Racing includes a high flow catalytic converter and resonator and bolts nicely between the OBX header and existing Roadstersport muffler.

    






 

The car originally was equipped with California emissions which includes two cats; one in the header and another cat further downstream.  With the aftermarket header install, I am basically converting the car to 49-State, or Federal emissions which only includes one cat and also relocates the oxygen sensors.

   With the heavy, restrictive OEM header gone, the car now breathes better and revs much more freely above 4K rpm.