TrueGS300

I'm onto upgrading my BOV now that I've got my wategate figured out. I'm pretty sure I want to go with the Tial Q. Of course I would need to aluminum weld the flange onto my IC pipe to run it. But there are several things I need to consider. Number 1, it is almost impossible to get an understanding of what spring pressure to run. Plenty of videos and faqs about what they do, but not how to select. See if I order one from MAPerformance, it only comes with the one spring selected. So I need to get it right. What determines the spring rate needed? Is it boost pressure, manifold vacuum, both? And whats the balance between the two? The Q is 50mm and can support up to 1800hp according to their website. But supposedly functions fine for any level with the right spring. 6, 8 , 10, and 11 are the selectable springs. If I want to run 20ish psi as my final goal, is there a way to determine which spring to choose?

Scigheras

BOV spring rate has nothing to do with boost pressure, it's all about manifold vacuum. Its only purpose is to keep the BOV shut during idle/cruising, when there's manifold vacuum. If you want to precisely determine what spring to run, look at your boost gauge to see how much vacuum you are pulling at idle. Boost gauge needs to be hooked up to the intake manifold of course, after the throttle body (where it should be anyways). If you have a BOV of a decent brand the manufacturer will be able to tell you what spring to run for the amount of vacuum you are seeing. I'm pretty sure Tial has a table for that somewhere on their website.

TrueGS300

Ok I got a better understanding of it all, thanks for responding. I'm going to wait till I get my wastegate replaced and the car running right to take a good manifold vacuum reading, then buy the BOV with the appropriate spring.