[Chambers]

A waste gate releases exes exhaust gases to stop the turbo from spooling up after a certain psi. You could buy headers for the turbo that have a flange built in for a divorced (external) waste gate, but you will have to keep the stock actuator on, just not connected to the pressure line, so the internal waste gate doesn't open. Or buy a manual boost controller that completely replaced the stock actuator, Greddy makes one, suprastore.com has them for like $190.

A blow off valve releases pressurized air out of the intercooler lines, when the throttlebody closes the air has no where to go, so a blow off valve is used to release that pressurized air so the turbo doesn't get compressor surge. compressor surge is when the pressurized air forces its way backwards through the turbo, this can destroy the turbo bearings. The factory "bov" on the Supra is actually a recirculation valve, it takes that pressurized air and feeds it back into the front of the turbo. The factory fuel maps correct for that increase in air, so you might need slight tuning if you put a bov on it, but I could be wrong. Hope this helped.