There are at least a dozen different springs for my Tial WG, in like 2 psi increments. You certainly can control boost with just the WG spring, and its a little better because its so simple. But you have no easy adjustability. Takes a good 10-20 minutes to change the springs.
I just dont understand why he went to a stiffer spring if he was trying to lower boost. Shouldve gone lighter. IF 10 psi is what he wants boost at, and the fluttering between 10-13 psi is the problem, well, I cant remember what causes that but I have seen it in on car. Ah yes! Its usually from running too soft of a spring and trying to run double or more with the MBC. Running a 10 psi spring at 10 psi should cause any problems, something else is wrong. I would check for boost leaks, and if that is ok, look into the tuning. Being very rich could cause that I suppose. Or too lean. Yeah, I'd get a WBO2 on it. Could also try an 8 psi spring and see if it will hold that. Might be something about that specific boost pressure the setup doesnt like.
This will be a tough one to do over the internet, but I'm sure this guy will be able to figure it out eventually.
