> Kind of hard to believe all this as the stock 90-91 engine only
> generates about
> 5 or 8 psi max. This is pretty much identical to what Francois is
> running
> with no apparent problems. Francois what is the diameter of your
> exhaust
> pipe after the turbine?

Not hard to believe at all, Series 5 is 8.5 psi from the factory,
limited by exhaust restriction, and also intake restriction.  This is
why opening the exhaust on a turbo RX-7 gives so much power.  Racing
Beat:

"The bolt-on exhaust system increases horsepower approximately 32% - a
59 HP increase on a 1987 Turbo II RX-7!"

Mazdatrix adds:  "Boost increase is 4-6 psi. Fuel  cut controller is
required to prevent fuel shut-off to rear rotor due to  the increase in
boost pressure seen by the factory computer"

Basically the factory wastegate is designed with the intake and exhaust
restrictions in mind.

Many have blown rear apex seals  on the 2nd gen turbos by using less
restrictive intake/exhaust and the factory computer computer shuts fuel
off to the rear rotor at around 11 psi, thus detonating the rear rotor.
  Stupid move on Mazda's part.

Hans