Tachyon56

Hey all, before I get people yelling at me for not using the search, I did. I am having troube understanding some of the technical terms used and what not.

Situation: I have a fully recirc BOV, running about 28 lbs psi on my FP Red. The BOV holds psi to max but flutters after I let off. The stock ofcourse doesnt do this, but stock is not strong enough to hold 28 lbs. Stock gives out at 26lbs, thus why I upgraded.

My question is, why is it fluttering after I let off? Too strong a spring? I have softer springs, and can adjust the springs even more with some shims (a coin shaped spacer). Problem is, the weaker springs will not hold boost. Is the fluttering ok?

Any input would be awesome. Thanks.

Golden

iTrader: (1)

The fluttering is ok. It happens because the new BOV reacts too quickly. An electrician would call it "Ringing". What happens is you let off throttle, causing there to be vacuum in the intake manifold and pressure in the intake pipes and intercooler. The BOV reacts to this and opens. The air vents and the BOV quickly closes. The turbo is still spooled and creates more pressure, and the BOV just vented a bunch of air into the turbo inlet. Pressure is quickly built in the intake pipes and intercooler again. So the BOV reacts quickly and vents the excess air and quickly closes. This repeats until the turbo stops spinning so fast / de-spools.

As you can see, nothing is hurt in the process.

The stock BOV doesn't do this, because it has a reference port that is connected to the back side of the diaphragm. So the stock BOV diaphragm sees Intake Manifold Pressure VS Boost Pressure. An aftermarket BOV diaphragm sees Intake Manifold Pressure VS Atmospheric Pressure. The stock BOV is simply held open easier and doesn't want to close so quickly.

What are the down side's do this setup? It can't hold boost nearly as well because the Boost Pressure on the back side of the diaphragm helps to open the BOV under pressure.

Tachyon56

thank you, I really do appreciate the info. I'm glad there are people here who can help the newbies.

E6-X

iTrader: (4)

so how to stop it from fluttering or which brand/type of aftermarket BOV to get or any other solutions ?

Clipse3GT

iTrader: (10)

APS Twin Vent is by far the best valve I used on X. Very hard to find one these days in the USA. But drives like stock and holds 30+ psi.

Mosaic

Golden, that is a remarkably informed statement. One of the few i have encountered regarding BOV operation in many months of BOV e-control R&D I have just completed.

I would like to add to it.

A BOV/CBV needs to do more than just vent surge in a performance car where time attack/torque matters. To date the trick is to balance BOV/CBV surge/spike response vs I/C pressure for ready boost as you clutch out at the end of a gearshift. In the regular mechanical valve systems a spring tension is used to balance these requirements by 'tuning' for your application.

Too much spring tension = poor spike/surge performance with good IC pressure.
Too little = Too sensitive to street driving - blow off under partial throttle lift, weak IC pressure
Just right = reasonable spike/surge with reasonable IC pressure - the compromise.

OEM BOV/CBV also add one more protection to the system - over boost limiting. This is why they leak at higher boost levels, they are so designed. Therefore adding an aftermarket BOV/CBV which does not leak can result in boost spikes which are quite dangerous.

In order to replace the stock BOV (which vents surge and provides overboost leaks) with an after market BOV (which does not leak) you must consider your drivability & engine safety compromises. Higher boost levels which must be managed is a given. One less layer of overboost prevention. Possible late surge venting, resulting in MAF transients /hesitation/ & emission problems.

Why do aftermarket BOV/CBV manufacturers not make a product that handles all three requirements? Because a mechanical BOV/CBV has no intelligence, to make it do 3 things instead of 2 will make it too pricey and therefore not sell. Ergo the customer has to pay $$$ for the best compromise.

Certain OEM car makers have now gone the route of the intelligent BOV/CBV, having it under ECU control. After all, almost everything else is under ECU control. It's the best way to manage performance vs emissions.

Why then are there no aftermarket BOV/CBV electronic control devices? Mainly because the existing mechanical devices are too SLOW/laggy to be helpful under E-control. A whole new generation of super fast mechanical valves need to reach the market before e-control can really work.

I mentioned R&D earlier. Soon there WILL be an option for performance vehicle owners and it sidesteps the issue of slow mechanical valves. The E-control will offer several features including the following:

1) BOV/CBV opens before Surge/spike even forms, not in response to it.
2) Tunable sensitivity and duration for your application's unique requirements.
3) Can close before you clutch out to provide ready boost in your I/C for best throttle response.
4) Can deliver Overboost venting at a tunable boost level.
5) In cabin tuning & presets.
6) All of the above are emission neutral or positive.

The preset allows you to drive a regular street tune and access a high performance time attack tune at the press of a button. The pressure built in the IC before you clutch out is dependent on several factors, including turbo a/r, compressor wheel size and IC volume. However, because the turbo is not being 'driven' during clutch out it cannot surge or spike, it will merely find a balance between its own inertia and the IC pressure.

I hope this helps and clears up why some BOV/CBV can cause drivability issues.

ScottSpeed21

iTrader: (7)

Usually it's the other way around, the BOV responds too slow instead of too quick. Especially with an adjustable valve, it's very easy to have spring pressure too tight, which causes a slow response and you'll get a bit of surge before it actually opens and vents the pressure. The best way to avoid this is to adjust the valve properly. It should be just barely tight enough to keep the valve closed at idle, and with a recirculated valve it's even ok to loosen it just a bit more and let it hang open a little. It'll still hold the boost, but less spring pressure will make it more responsive.

I do agree though, a little off throttle surge doesn't hurt anything.

arghx7

The Taurus SHO already has dual fully electronic BOVs:

Mosaic

Yes...OEM are all heading that way, of course, what about the installed base of performance cars? That's what this product is aimed at, the aftermarket for those cars that don't yet have it, which is most of us.

ZEKE010

iTrader: (6)

interesting.....
when do you estimate yours to debut and what is the projected price?

Mosaic

Within a couple of months, I can't discuss price here, this is not a commercial post.

linste

I got the APS as well and installed in this weekend. At part throttle its flutter alot (like 4-5 tsh tsh) but at high boost its more of a uniform blow off sound. All mean while driving completely like stock. So i guess thats good? as long as driveablity is fine - even though alot of flutter?

thx

elusiveGSR

iTrader: (1)

synapse works well for me.

derekste

iTrader: (9)

what? you totally lost me here... I've never seen a (mechanical) BOV that didn't have a reference port off the intake manifold

all blowoff valves have 3 connections:
a- charge side (pressurized intercooler piping)
b- vent side (either recirculated or vented to atmosphere)
c- reference port connected post-throttlebody

bov has a piston with spring/diaphragm that can hold a certain amount of boost on its own (say 7psi/.5 bar). when the turbo is spooling, this is just enough to get to the point where the intake manifold has pressure which goes through the reference port and keeps the valve closed. in other words, manifold pressure + spring pressure is always greater than charge pressure. when you let off the throttle, the throttle body closes, reference port is now under vacuum, so the charge pressure is now greater, and pushes the BOV open to vent the charge.

why you would ever want to electronically control the blowoff valve is beyond me, unless you were trying to build in additional overboost failsafes. car manufacturers have been doing this for years... my wife's 99 saab 9-3 viggen has a solenoid like this, as does the hyundai genesis coupe I believe.

oh, and the stock BOV will hold 30+ PSI just fine if you crush it in a vise... old DSM trick :P

Golden

iTrader: (1)

The Diaphragm / Piston has to have a reference for the back side.
The front side's reference is the intake manifold. So the back side needs a reference and we can choose from either atmospheric pressure like most all aftermarket BOV's have or we can choose to use boost pressure, which the stocker uses.

Lets picture what is happening in the stock BOV when we let of the throttle with a fully pressurized system. The piston that is holding back boost has full boost pressure pushing back against it. The diaphragm has a hose connected to the intake manifold. The back side of the diaphragm has boost pressure on it trying to force the piston shut. Now, right before we let off the throttle, the top / intake side of the diaphragm has full boost pressure on it. The diaphragm has equalized pressure on both sides and it is solely the spring that is holding the BOV shut. As soon as the intake manifold creates vacuum, the top of the diaphragm will contain vacuum and the back side will have full boost. This will instantly open the valve up fully, and the system will vent. The back of the diaphragm will settle down to atmospheric pressure and the spring will force the valve close even if the intake manifold still has vacuum.

Ok, still with me?

Now with an aftermarket BOV, the back side of the diaphragm will have atmospheric pressure. So before we let off the throttle, the piston has full boost pushing on it, the top of the diaphragm has full boost holding it shut because the back side is atmospheric pressure and has less pressure than the intake manifold side. Note that a spring is not needed to hold the valve shut, as boost pressure vs atmospheric pressure will do this for you. As soon as you let off the throttle and the intake manifold builds vacuum, the top of the diaphragm will have vacuum and the backside of the diaphragm will still have atmospheric pressure. The vacuum will instantly open the valve and the system will vent. Spring pressure is required to keep the BOV shut during vacuum operation.

Make sense?

The BOV with atmospheric pressure reference will be able to hold much higher boost, because boost itself is holding the valve shut, where as the BOV with boost reference will require spring pressure to hold the valve shut. Spring pressure does not scale with boost.