If you have a 1990-1997 Miata (NA), your car came with a return fuel system from the factory. Since the K series uses a returnless system, you'll need to convert your fuel system to returnless as well.
We recommend the FUELAB fuel pressure regulator to do the job. Once installed in your fuel system, you can set the fuel pressure to 60 psi and you'll be ready to go.
This regulator uses -6 AN inlets (FUELAB part 51502-1)
Note: 1999-2005 Miata (NB) customers do not need this regulator since the fuel system is already returnless from the factory.