No Compression Surge Or "flutter" With Blocked Bov

[crankyfrank118]

Yea no flutter ever. Just a gush from the pod.

[XGTRX]

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.

[89CAL]

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

[Missileman]

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.

[Missileman]

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.

[XGTRX]

But then the turbo will break when it spins backwards

According to Facebook, yes u are correct.

[emoji1] [emoji1] [emoji1]

[XGTRX]

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.

[Missileman]

Block em off like Jonny said with a coke can gasket, then go for a run and see if there is much difference.

[Dose Pipe Sutututu]

Stock turbo doses the best, I know

[Dose Pipe Sutututu]

back in the days when my piece of shit was even more of a piece of shit... but it dosed hard

No Airbox Lid:

With Airbox Lid:

And Last Year:

[crankyfrank118]

Haha mine def dosent sound like that!

[Dose Pipe Sutututu]

aluminium can between BOV & flange like I just said man!

[XGTRX]

https://youtu.be/Ye9ctbLqEq0

[niZmO_Man]

My stock BOVs are fine .

[XGTRX]

Just blocked off my BOVs for shits and giggles. Surprisingly transient response at part throttle has improved.

[Missileman]

What boost are running?

[XGTRX]

Only 19ish with a bleed valve, ebc not right yet. But I feel the difference that for sure.

[Missileman]

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.

[XGTRX]

Yeah I noticed the plungers were pretty close to the edge of the outlet. But I never had a problem holding boost so I assume they are OK. I will lube them if I decide to go back.

[Missileman]

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 May 30, 2016 by Missileman