My old Deltagate had a plate sitting on top of the spring (below the cover) and a bolt that could screw into the cover and compress the spring to give it a stiffer rate for more boost.
Has anyone tried doing the same to a Tial?

I've also just thought about finding a big washer to shim the spring but the other idea makes it adjustable.

 

There is no screw on a Tial to make it hold more boost. I am sure you could probably put a washer in there and make it hold more but why not just buy a manual boost controller or a heavier spring and do it right? Neither are that expensive.

 

Right now I'm using the cheap ebay BC, but it's unreliable. Every now and then it'll hit a 5psi spike. I really don't trust any of them.
However, the screw method is extremely reliable and is as adjustable as a regular BC.

 

why not just buy a new wastegate spring. im pretty sure you could have gotten one for the price of that ebay bc