As big single turbo RX-7s are so common, it’s easy to forget that the FD comes with a very clever twin sequential turbo setup from the factory. Rather than two different sized turbos, the FD runs two identical turbos and a set of solenoidcontrolled valves. That means it runs off one turbo at lower rpm, bringing it on boost at very low rpm, gradually bringing in the second turbo as the rpm rises, giving great high rpm power.
While often disposed of, as the solenoid control parts are complex and well known to go wrong with old age, the factory twin sequential turbo setup is capable of far more power than many might think.
The current record using the standard twin turbos in full sequential mode is a quarter mile time in the mid 10-second range at around 130mph, which is modern hypercar fast but from 1990s-era standard twin turbos!