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But in all seriousness. I don't use any bov, never will again. They all leak and cause serious lack of power around 10-30% throttle.

That's just my personal opinion

But I thought they help with transient response.

I would expect the stock BOV to open when boost in the cooler pipes, purely because of the softness of the spring

An aftermarket BOV adjusted to a hard setting is more likely to stay closed

The stock BOV's do have that little bypass hole as well, wether that makes a difference or not

BOV's work off pressure differential. Imagine for arguments sake the spring is worth 2psi, so with the car boosting it has 10psi on the cooler pipe side and 10psi on the top of the valve, so with the spring 12psi on the top, obviously 12 beats 10 so BOV stays closed. Close throttle, vacuum occurs in the manifold so now you have 10psi on the cooler pipe side and -10 on the top of the valve + 2psi so therefore -8psi

With the boost/vac line removed, you only ever have the 2psi of spring pressure holding it closed, so as soon as there is any more than 2psi in the system the valve will open

These are just rough numbers, but remembering how soft the stock BOV was to open by pushing it in with my thumb, I would suspect it would stay open alot

So really what you should have is a whoosh of air then possibly a small flutter at the end when the spring overcomes the valve. Although then you have to think about the effect the low pressure/vac that is present in the recirc pipe is having

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But I thought they help with transient response.

Pretty sure Tom said he's using an auto, but with a manual yeah when you get off the throttle when changing gears the recirculation valve will stop the compressor from stalling.

I would expect the stock BOV to open when boost in the cooler pipes, purely because of the softness of the spring

An aftermarket BOV adjusted to a hard setting is more likely to stay closed

The stock BOV's do have that little bypass hole as well, wether that makes a difference or not

BOV's work off pressure differential. Imagine for arguments sake the spring is worth 2psi, so with the car boosting it has 10psi on the cooler pipe side and 10psi on the top of the valve, so with the spring 12psi on the top, obviously 12 beats 10 so BOV stays closed. Close throttle, vacuum occurs in the manifold so now you have 10psi on the cooler pipe side and -10 on the top of the valve + 2psi so therefore -8psi

With the boost/vac line removed, you only ever have the 2psi of spring pressure holding it closed, so as soon as there is any more than 2psi in the system the valve will open

These are just rough numbers, but remembering how soft the stock BOV was to open by pushing it in with my thumb, I would suspect it would stay open alot

So really what you should have is a whoosh of air then possibly a small flutter at the end when the spring overcomes the valve. Although then you have to think about the effect the low pressure/vac that is present in the recirc pipe is having

Even more so if the diameter of the diaphragm is lager than the seating surface of the valve.

Pretty sure Tom said he's using an auto, but with a manual yeah when you get off the throttle when changing gears the recirculation valve will stop the compressor from stalling.

Hmmmm. I am in 2 minds atm. In a GTR I have the BOVs venting in the guard and considering removing them altogether So the question is whether or not I will see a noticeable change in transient response on part throttle. Any advice would be great.

I blocked mine off this arvo and noticed zero difference, 14 psi, breed valve, auto trannie. Have you tried lubing the shafts on the rec-valves with some molly grease? mine used to stick a little open until I lubed it.

Not much Sutututu either, stock intake pipe and airbox.

Did some quick calculations on my rb20 rec-valve,

Valve seat is 1" diameter = 0.785² inches x 14 = 11lbs

Diaphragm is 2" diameter = 3.14² inches x 14 = 44lbs

estimated spring pressure 10 lbs

so when at 14 psi boost, there is 44lbs pushing down from the diaphragm, 11lbs pushing up on the valve face, then add another 10lbs down for the spring

so thats about 54lbs down compared to the 11lbs pushing back up from the 14psi of boost.

To see how that changes at intermediate throttle positions you would need to put another pressure gauge before the butterfly in the throttle body, needless to say as soon the plenum approaches atmospheric pressure only the spring will be holding the valve closed.

Please correct me if my physics is off ;)

Edited by Missileman

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