What do I need with a full exhaust for a Mazda RX-7 FD?

The available data only mentions an extreme custom FD application—a semi-peripheral port 13B with a Garrett GT47 turbo—where 3", 3.5", and 4" stainless steel piping are considered, but no definitive size is established ³.

However, there is a critical technical consideration to be aware of when installing a full, free-flowing exhaust on a turbocharged rotary: the increased flow frequently causes boost creep. To safely manage this, you will likely need to:

• Port the wastegate to handle the exhaust flow and stabilize boost levels ⁴.
• Install an Air/Fuel Controller (AFC). If you are hitting fuel/boost cuts, do not just install a fuel cut defender on its own. Tricking the ECU into reading lower boost without properly managing the fuel maps will cause the engine to run lean, which can easily result in a blown engine ⁴.