I'd guess 60 PSI in the back tires to perform that silliness, although it does take reflexes to pull it off in that car. We had a RUF conversion 930 in the shop back in the 1980's that belonged to a Belgian who told me to drive it and keep it from getting rusty. Mostly, that car just scared me. Driven in anger, that thing was beyond my skill set. IMHO the shift linkage and the spring rates needed to be tweaked to make it a little more "friendly."

Of course, every time we drove it we twisted the waste gate down. It would compress the engine mounts and subframe would bottom out against the unibody. At 3,300 RPM the boost would come on so strong that you could actually hear the mechanism in the factory gauge go "click" as it struck the side of the housing at it's limit.