Tightening the spring rate on the aftermarket BOV will do the same as blocking off a stock BOV
so for example your running 10psi
and the spring on the BOV is the hardest/tightest as it will go
then you go for a spin
from one gear to another you only hit 7psi
now the 7psi wont be enough pressure to lift the spring in the BOV so it will do what a blocked off stock BOV does and flutter
I had a GFB Stealth FX on my car and it did exactly the same thing
I have not encountered any drivability issues since i blocked off my stock BOV Chad
if anything i would say that boost comes a little bit quicker and earlier
so i have not lost anything but gained by blocking off my BOV
I have encountered no problems with doing that mate
no stalling or idling problems
and it also hasnt changed anything like my AFR's
Chad, Pete and Luke saw my car on the dyno last saturday at the PGA dyno thingy
and according to them and the dyno result my car sounded and ran fine