When I was making a wastegate for my 93 with GM-3 I found that a spring that would crack/compress at 16 in/pds would get me 8psi boost. Boost lever and spring in stock location and angle . Not sure why I got different figures than you, maybe differant turbo and not talking apples to apples?
1993 F 6.5 turbo/desiel 3/4 ton HD, long box, 2wd, 4L80E trans., 3:42 rear gears, 170,000 miles, Heath 4" exhaust, dual thermastate/HO water pump upgrade, DB2 pump turned up 1/4 turn, 97+ air cleaner, removed snorkle, Autometer EGT/Trans/Boost gauges, manual torque converter lockup switch, Heath turbo master, Okanagan BC. Canada
86 Monte Carlo SS, Original Owner 55000 miles. 2002 Dodge Dually 3500 24v cummins
00 Dakota Sport 90000kms 4.7l, 97 Grand Prix GT, 05 Bigfoot truck camper, 56 Ford f600, 02 Polaris Scrambler 400, 97 Polaris 900 watercraft, 97 Yamaha 700 Mountain Max.