The FC3S side housings do not lend themselves to massive street or extended porting of the original intake ports.  We define "intake ports" as the teardrop openings on the "inside" of the motor rather than the intake passages that mate to the lower intake manifold on the "outside" of the motor.

Porting the intake ports primarily consists of opening up the "top" of the intake port.  You can port the "back" of the stock intake ports, but be aware that the path for the corner seal runs a few millimeters behind the intake port itself.

Do NOT port on the side that is closest to the center of the housing - the oil rings run right inside of this edge of the port; if you start exposing the oil rings, you'll end up fuel bypassing the oil control rings and diluting your engine oil.  Try not to port "downwards", as this increases timing overlap between intake and exhaust periods; as a rule for forced induction applications, try to keep timing overlap to a minimum.

Some folks even recommend a radical bridgeport.  Bridgeports tend to be pretty fragile, so it's not recommended for a street application.  The bridge tends to crack, and when it does crack, it's time for a rebuild!  The bridgeport also creates more overlap by opening the intake period a lot earlier than stock. 

FC3S Pro:  Intake Porting
Custom "CZ" intake port template
I like to create intake porting templates from acrylic (Plexiglas) or polycarbonate (Lexan) as the clear characteristics of these plastics gives me a good idea how the port will look versus stock.
Stage II intake porting completed on primary intake port
The pic sizes are small for a reason.  I charge for this porting, so I like to keep my porting details a secret.
Another pic of the Stage II primary port at a different angle
Comparison of worked port and unworked port
Notice the casting imperfection on the bottom of the passage on the right-side, untouched passage.  The left-side, ported passage has this casting imperfection eliminated.  Sorry for the blurry pic!
Another pic of the comparison
You can clearly see that the right-side, untouched passage has a slight bevel to it; the left-side, ported passage has this section eliminated.  Sorry for the blurry pic!
Two primary intake ports on the intake manifold side
I spend a lot of time getting rid of the imperfections in the passages; on average, I spend about one hour for each intake port
Custom "CZ" intake port template placed on stock Kouki FC 13BT primary intake ports on center housing
The difference in port opening is 10° as stated from the Mazda factory service manuals.  This means the earlier Zenki 13BT turbo engines run larger stock ports on the primaries!

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