• 13mm wrench or socket + ratchet
  • pry bar
  • die grinder
  • carbide burr

  • Labor:

    The 1989-1991 Kouki FC3S turbo wastegate design is superior to the earlier 1986-1988 FC3S Zenki turbo wastegate design.  The Kouki wastegate had two holes that allowed exhaust gases to bypass both turbine passages within the "independent twin scroll" turbo.  In contrast, the Zenki turbo wastegate only bleeds exhaust gases from one passage of it's "twin scroll" turbo - this inferior design will produce boost creep from freer flowing exhaust systems!  Boost creep is BAD.  Below is a desciption of how we port the Kouki wastegate passages to promote better boost control by the wastegate system.

    FC3S Pro: Kouki Turbo Wastegate Porting
    Kouki turbo turbine housing removed
    The turbine backing plate has been removed via a pair of 13mm bolts.  I am holding the external wastegate lever open.
    Wastegate flapper
    I am now holding the wastegate flapper door.  Notice the flapper can't open any further due to the turbine housing design.
    External wastegate lever pried open
    I am using a pry bar to bend the wastegate lever a little so that it'll clear the turbine housing.  This allows the flapper door to open to allows better access to the twin wastegate passages.
    Flapper at maximum travel
    After bending the wastegate external lever, this is how much the flapper can open.
    Don't forget to bend the lever back to it's original position!
    Twin wastegate passages exposed
    The twin wastegate passages are now easily accessible for porting.  A rubber band is used to keep the flapper open.
    Porting with a long carbide burr
    Shown is a Makita electric die grinder with a long carbide burr.  This set-up allows deep access to the wastegate passages.  Notice, the plastic wire tie used to keep the flapper from closing.
    Initial porting
    This is the initial porting to the wastegate passages.  Notice the faint outline of the holes on each passage - you can safely port up to there.  For more aggressive porting, you can port larger!  Due to the flapper design, there is no way the flapper can get jammed inside the two holes.
    Backcutting of first passage
    This is the shorter wastegate passage.  There is a lot of material you can remove from this passage.  The longer passage passes over this shorter one, and you can't port too much from the longer passage.  Shown is the backcut passage for smoother exhaust gas flow exit.
    Backcutting with light
    This is basically the same view as above, but with a light to illuminate the backcutting clearly.
    Both passages with light
    Both wastegate passages illuminated with light source.
    Finished porting
    Although not obvious, I took out a lot off the shorter wastegate passage.  The longer wastegate passage could not be ported that much due to insufficient thickness - I didn't want to chance potential cracking, since there were already cracks on the outside of the turbine housing.

    The FC that this wastegate porting was done to "unfortunately" had the wastegate rod fall off the wastegate lever.  The clip that normally holds the rod in place was not installed.  The FC was still going through break-in procedures (about 500 miles on rebuilt engine - rev limit at 6kRPM), so the boost loss was not a big deal.  With a Défi boost gauge monitoring boost levels, the FC with the unsecured wastegate managed to produce only ONE psi of boost!  The exhaust is a 3" straight through exhaust, with a 3" downpipe flowing through a single muffler.  This is a testament on how effective the wastegate porting can be on this Kouki turbo wastegate...

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