951 shimmed wastegate tell me more

[paul r]

My wastegate must be weak I get 0.7bar intitially, but this soon falls down to a disapointing 0.3bar as i approach the redline. My car is a standard '86 951. Since I'm going to have to pay for a refurbished wastegate anyway I thought why not get a shimmed (preloaded) refurbed unit. I guess theres little difference in cost.
My questions are who can sell me one?
How much cost?
How much boost?
Do I need to also use a bleed valve on the air pipe to the wastegate?

[Blackfoot]

if you get the weltmeister chips from autothority ($399), they come with a wastgate shim. my only other mod is a boost enhancer ($89) from lindseyracing.com, and my boost doesn't drop.

another solution would be to get an aftermarket wastegate, like lindsey racing's: