Is there really any performance advantage to tightening the spring as tight as possible without causing comp surge? Or is it just to prevent it from opening under boost?

I've heard many conflicting arguments such as, if it is set as loose as possible, then all the air would be released when it opens which will leave the compressor wheel free to spin without resistance so you can rebuild boost quickly once you're in the next gear.

The other argument is if you tighten it as much as possible it won't open as much and you will retain most of the boost pressure behind the throttle body so that the second you open the throttle again, you have all your boost back.

Are any of these points valid and what should I do with my Greddy Type-R?

 

as tight as possible without obvious compressor surge is the way to go. put a pressure tester on your car and start fiddling with the BOV adjuster and you will realize how easily it can leak.

 

Is it possible that it would flutter a little if tightened enough? I don't mean comp surge, but rather the bov opening and closing rapidly. I don't think the Greddy Type-R is supposed to flutter like an SSQ but I've seen some videos where it does. Any explanation for this?

 

If not tightened enough it could flutter while under boost, it would be working kind of like a pop up valve. opening and closing as it bleeds off pressure and reseals. Many BOV's use positive pressure on the back side to keep it closed in addition to the spring pressure, then once the throttle is closed the vacuum helps pull it open along with the force of boost pressure. If your BOV is too loose and leaks under boost you will lose power and cause your turbo to work harder.