The Twin-Turbo setup for the FD's was designed to operate well, but unfortunately at the cost of reliability. The stock turbos are known for failing, when I say turbos I mean everything that is required to run them.
http://www.rx-7tt.freeservers.com/rx7stuff.htm
I would recommend replacing the stock twin turbo setup in favor of a single turbo, with decent CFM but set it at a low boost setting. I would suggest something like a Greddy T78 setup, or something similar.
This way you can buy the greddy profec A and remote switching button thing so at a press of a button you can be running 21psi
btw, this all costs money. lots.