Ok so best I can figure it in a twin Turbo blow through system that uses a single fmic only one BOV is necessary as it is plumbed into the intake pipe before the plenum and after the fmic, that being said most of the BOVs I have seen the springs are rated at 11psi or less. I'm not planning on running much more but I'm wondering if I'm interpreting this rating wrong? Will this cap the system at the spring rating or just begin to relieve pressure? Will it only actuate when the throttle is closed and there is that amount of pressure? Is it a way of measuring vacuum? I understand what the BOV does I'm just confused as how the spring is used to accomplish it. Corky and Google have been no help....
Can anyone explain BOV spring ratings to me?
- Thread starter Jimmy
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dgc333
Well-Known Member
The BOV is referenced to the intake manifold so when the throttle is closed and manifold vacuum is created it opens releaving the up stream boost so the turbos don't see a shock and stop spinning.
The spring keeps the BOV closed so you don't bleed off boost and needs to be sized to a little more than the boost you want to run.
The spring keeps the BOV closed so you don't bleed off boost and needs to be sized to a little more than the boost you want to run.
Mad Dart
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The Blow off spring is rated at a certain pressure in your example, it is 11psi. There is an adjustment screw on the top that will most likely get you another 10-15 lbs above the springs rating. Turn it clockwise to compress the spring which will put more pressure on the valve and keep it closed longer. When you let off Vacuum will pull the valve open which will relieve the pressure to the turbo's
When mine was on the dyno a few weeks ago, at idle both blow off valves were open. I was pulling about 22psi vacuum. I think I have 12lb springs in them. So I just loosened the jam nuts on the adjuster's and turned them 3/4 of the way in which kept them shut. If the throttle was wrapped on and then shut, the spike in vacuum went above 22psi for a brief moment which pulled both valves open instantly and then they would close immediately afterward.
When mine was on the dyno a few weeks ago, at idle both blow off valves were open. I was pulling about 22psi vacuum. I think I have 12lb springs in them. So I just loosened the jam nuts on the adjuster's and turned them 3/4 of the way in which kept them shut. If the throttle was wrapped on and then shut, the spike in vacuum went above 22psi for a brief moment which pulled both valves open instantly and then they would close immediately afterward.
Mad Dart
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There are other variables such as where the BOV is positioned also. This would only be a starting point. The 11psi Spring may work out just fine after adjustments.
Oh and Mad while I'm on the subject am I correct in my assumption I only need one BOV? I realize you have two because you have two inter coolers but is that the only reason? Do you think each turbo needs it's own for equalization? Or even in your setup couldn't you get away with one if it were plumbed at the plenum?
Mad Dart
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I am sure you can get away with 1 BOV, alot of guys run 1 even with a TT Set up.
The only reason I ran 2 is for the uniform "look" and that is it.
The only reason I ran 2 is for the uniform "look" and that is it.
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