Ok it's a home built s5 to4b vtrim hybrid, I blocked off the internal gate to the outlet, took out the flapped and enlarged the ports 1"+ each, drilled a hole in the back plate, and welded a 1.5" runner to the wastegate. I'm running a tial 38mm wastegate with the small green spring .5 bar 7.25psi. Engine is a large street port s5 TII and race port exhaust. Stock tmic, rtek 1.7 550/ID1000, aeromotive 340lph, 3" tid, 2.5dp, 3" straight single exit. It's creeping past 15psi in 3rd 1/2-3/4 throttle. I'm not going past 6500rpm. I have a afc that I trimmed up 3000-8000rpm on the high side. I'll have my wideband in soon. Maybe I just need to go all out to a aftermarket mani :/ idk

 

i'd say go for a larger wastegate or add another one. usually in a lower boost setup one large wastegate or 2 smaller ones are used so more exhaust flows through when they open keeping boost creep and spikes down

 

sounds like you need to revise your porting to the wastegate as it sounds like it's not flowing well enough, that or your wastegate line is not plumbed to a pressure source properly.

 

Yeah I thought about many of those things, I'm running a 2" dia restrictor plate on the downpipe. Still creeps, it vents open so I hear it right at 7psi. I'm thinking about going through the runner to the other side and further increase port area.

 

This still had boost creep to 17psi with 3 1/2" exhaust, but it did hold down to 12psi with a 3" RB RevII turbo back exhaust.

Porting the manifold and turbo runners up to the wastegate passages will drop the velocity and improve flow to the wastegate runners, but it will decrease the turbo response as well- so do that as a last ditch measure.