The Tial Q valve is Tial's newest blow off valve. Improving upon their old design that has been proven for over nine years to be one of the best performing valves on the market. They were able to design this valve to flow 60% more than the original design. The Q valve uses the same flange as the original version to allow for an easy upgrade.
The spring pressure in the valve does not correlate with the amount of boost pressure you want to run. The size spring you need is determined by your engine vacuum at idle. Please refer to the charge below to select the right pressure for you.

ENGINE VACUUM READING SPRING COLOR SPRING RATE -22 and -23 in/Hg Brown -12 PSI (-24 in/Hg) -20 and -21 in/Hg Yellow -11 PSI (-22 in/Hg) -16 and -19 in/Hg Un-painted -10 PSI (-20 in/Hg) -12 and -15 in/Hg White -8 PSI (-16 in/Hg) -8 and -11 in/Hg Black -6 PSI (-12 in/Hg)