I agree with John Sargent, the factory setting is 7-7.5 lbs. There are numerous ways to increase boost the easiest being the G valve, the hardest but safest is perhaps the Saab APC adaptation, the most expensive being Volvo's factory boost system. The 86 model might not be the best for higher boost as Volvo modified their design in the following years to provide more durability. I recently tried something that it feels (a day later) to be increasing the boost response and is very simple: the addition of a PVC valve in the line between the intake manifold and the crankcase ventilation system set to keep boost out of the crank. I don't know why but the response seems quicker, perhaps because the boost doesn't leak out to the crankcase. See my previous post of 12/26 "Oil Burning Turbo" for more details. I'd love to have John's thoughts on the PCV addition.
89 745 TIC/APC 190K miles