Tial Q 50mm BOV Limit?

[dacowgod]

I am running 40-42 PSI on a Holset HX-40.

I currently have a greddy type RS installed... it doesn't take it to well.. I will hit 40ish and quickly drop as the BOV will not stay shut.


So anyways I am going to need to upgrade the BOV ... I believe I want the Tial Q 50mm .. .. their spring rates are rated by how much engine vacuum you have obviously because they open via vacuum.

Does that mean the spring does not assist much in holding actual boost?? I need a BOV that can hold 45-50psi of boost w/o leaking... my gut makes me feel like I need to put the stiffest spring possible in the BOV, but directions indicate that would basically set me up for failure when it came to opening...

If i am going by directions... I feel like i should put the smallest spring rate in.....but then my gut says its going to leak like my greddy RS is doing...

Anybody have any experience on these BOVs at over 40 psi and what spring is ideal at that pressure??


Thanks in advance.

 

[nikkeebabee]

I'm running a tial with a 6psi spring and running 34psi without issue... I will be cranking it up next year to past 40 and don't expect any issues... Remember there is boost flowing thru that vac line to keep it closed. You'd shouldnt have an issue...

 

[donniekak]

I have used a tial at those levels and saw no problems. Under boost even a very light spring will keep a good bov closed. The pressure from the manifold line to the back of the diaphram balances the boost seen by the piston. When the throttle plate is closed, the pressure in the piping is higher than the manifold pressure, this causes the piston to move out, and the valve blows off. The problem with bov's leaking is more of a sealing issue with the piston than blowing open.

 

[JusMX141]

I'm sure the "Q" uses the same piston, but the standard 50mm Tial even has an o-ring at the bottom of the piston where it seals against the base of the valve body. When this valve is closed, it's f-in closed.

 

[2gGSX]

The spring is only used to keep the BOV closed during idle. That's why they rate them by engine vac instead of how much boost you plan to run.