[Mike the mechanic]

A turbo car uses its boost to accelerate (under load). It doesn't necessarily need full boost to sustain a constant speed, where the only load is wind resistance. I haven't tried this on a 930, but my own Carrera 3.2 turbo uses full boost to accelerate to top speed (5th gear rev limiter set at 7000rpm) but once the speed is reached, the load on the engine drops significantly and boost drops down to almost atmosperic. All my turbo cars were like this. The only cars that will run on full boost are cars that have undersized turbines on their turbos.
By the way, the 3.3 turbo intercooled makes about 135 hp without any boost.

Mike
86 Carrera t