Here's what's inside a ZEX nitrous control unit

[probedude]

Looked up their patent which described how they "compensate the fuel flow
based on N2O bottle pressure"

http://www.delphion.com/cgi-bin/viewpat.cmd/US05967099__?MODE=fstv&OUT_FORMA
T=pdf

There is a manifold that is fed nitrous after the solenoid through an
orifice.  This manifold is then bled to the atmosphere through another
orifice.  The manifold pressure is then fed to the stock fuel pressure
regulator.

FYI, the one bad thing I found out about the ZEX unit is the lack of a low
fuel pressure cutout switch.  If you blow the vacuum/pressure line off your
fuel regulator - you're going to be running really LEAN.

Dave
(finished my O2 sensor monitor, RPM valid window circuit, and TPS sensor
circuit.  Time to lay out the PCB!)