BTR starts with the basic NOS kit, which is a dry setup, with a TPS WOT switch,
and a electronic fuel enrichment module that taps into the intake air sensor
wire and the coolant wire - to fool the PCM into keeping the injectors open
longer. Then it adds propane as a fuel source to push it beyond the limits
of a dry only setup. Propane also has an octane rating of around 102.
Because propane pressure is limited to around 200psi, its upper limits as
a single stage HP source is around 200hp, so for an extra kick(and extra money), BTR has a gasoline stage add-on.
The basic NX setup is (someone correct me if I miss something) a wet
kit with a manual throttle WOT switch. The gasoline can be provided by tapping into the fuel plug on the intake, or a fuel cell with a pump to provide pressure.
Once you obtain either basic kit - NOS or NX, there is almost no limit
to your ability to customize or upgrade. You can even put a kit together
yourself and replicate what is available in kit form.