Wobble's guide to setting up your bov properly..

[Wobble]

Ok.. where to begin..

Ive been having a beast of probs getting my greddy type-s set right, so i did some deductive reasoning and testing and figured ALOT of things out..


1: the pressure from the TB hose is what holds your BOV shut.. NOT the spring.. what this means is that the only reason you need to crush a 1g bov is NOT to hold more boost. but more vaccum..

the spring has to be set JUST strong enough to hold shut under the amount of vaccum your car draws at idle.. 1g bov's will leak on 2gs at idle because their spring is designed to hold LESS pressure because the 1g motor creates LESS vaccum at idle than a 2g because of the lower compression.. NOT to hold more boost..

When you build boost it is also building up in the vac line that runs to your BOV.. there will ALWAYS be just as much boost in that vac line as is in your intake/ic pipes.. so if your running 20 psi there will be 20psi of pressure being generated holding your BOV SHUT+the tension generated by the spring.. so even if your spring is VERY soft, just the pressure alone will be enough to keep your bov sealed under boost.


ok not the big boy, this is IMPORTANT!


This is for the Greddy Type S bov, but probably pertains to most any adjustable one.

this is what you do.. PERIOD!

IF you have a MAS system (stock) leave the LOWER nipple (if applicable) vented to the atmosphere::

1: YOU MUST RECIRCULATE PERIOD.. you will NEVER get a good setting if you vent.. youll see why..

2: undo your dump tube from the bov outlet/purge and plug the hole leading into the MAS this will ensure a steady idle (dont want any unmetered air causing spastic idle and thus spastic vaccum)

3: start your car and let it reach operating temp. and idle.


4:loosen the lock nut (if applicable) and get a flashlight

5: slowly loosen/decrease the pressure on the spring untill the plunger begins to open a SLIGHT amount.. do this VERY slow as the bov may react slowly due to commin vac irregularities..

6: once it has just SLIGHTLY cracked open.. just a tiny bit.. lock this in positiion..

7:reconnect everything.. your done

what you have done was set the bov to the optimum tension for YOUR car.. all cars are different.. even of same make and modle due to mods and engine condition. so yours wont match your friends..

now, your BOV has just enough tension to stay pretty much closed but will open quickly and easy to prevent partial throttle studdering and compressor surge.. IT IS OK THAT AIR IS LEAKING THROUGH IT SOME, because the air that is being "leaked" is metered air, not outside unmetered air, so it wont effect your idle at all.. this is why you MUST recirculate.. if not this would be unmetered nasty air.. bad air.. the devil's air..

now you see if your vented to the atmosphere.. that slight crack will draw in unmetered air.. and that sucks.. period..


If you are using a VPC or other Vein pressure type airflow meter

1: plumb the bottom nipple to your lower IC piping, do not vent..

2: do the same as above except when you fin where the BOV opens at.. turn it back till it closes completely.. and then give 1 good turn on the screw.. this will ensure a good seal at vaccum but will still allow for smooth operation..


thats it.. hope this has been of some help. there seems to be soo little info about what is good and how to set these things up.. so.. here we go..


oh yea, and you might not get the PREFECT setting first try, this is to get you VERYclose, do some road testing and fine tuning to get it just right for you.. but this will get you VERY VERY close

 

[RuBiCaNT5X]

My only beef with your tech article is that when your BOV leaks, your turbo has to work harder to make the same psi than if it were closed completely. Think about it, when you send forced air through your IC piping, it's a pressurized system. when the BOV leaks, it lets air back into the intake which is not supposed to be pressurized. The air gets sucked back into the turbo to be recompressed. Your turbo is thus working a lot harder to keep the same boost level and will probably shorten it's life. I have the Greddy Type-S (wish I didn't), overall it's not a bad recirculating BOV, but it's design is lackluster. The flutter that all Type-S' are prone to wears out the diaphragm which leads to tearing. I have the lower nipple hooked up on my Type-S and it did leak a bit. I was getting P0120 errors every day (Throttle Position Switched Circuit Error) until I pressurized the lower barb. The BOV opens more evenly that way. As for the leaking, I cranked it down a bit (4 threads showing) to prevent the leak and now it runs like a champ. I am by no means an expert, these are just my humble observations since I've had my car...

 

[kpt4321]

Originally posted by Wobble
1: the pressure from the TB hose is what holds your BOV shut.. NOT the spring.. what this means is that the only reason you need to crush a 1g bov is NOT to hold more boost. but more vaccum..

Nope. The pressure in the manifold AND the spring hold the BOV shut, you need both. You cruch a 1g MOV to stay closed at idle, and to keep it from leaking, and to keep it closed at part throttle.

1g bov's will leak on 2gs at idle because their spring is designed to hold LESS pressure because the 1g motor creates LESS vaccum at idle than a 2g because of the lower compression.. NOT to hold more boost..

Can anyone verify that 2g's have higher vacuum at idle?

there will ALWAYS be just as much boost in that vac line as is in your intake/ic pipes..

Not true. Unless the throttle is all the way open, the pressure in the intercooler pipe is NOT the same as the pressure in the manifold, and the pressure in the hose to the BOV.

 

[Wobble]

Not true. Unless the throttle is all the way open, the pressure in the intercooler pipe is NOT the same as the pressure in the manifold, and the pressure in the hose to the BOV.

ture.. sort of, but the added pressure of the spring (= to about 16 psi minimum will more than offset this)

My only beef with your tech article is that when your BOV leaks, your turbo has to work harder to make the same psi than if it were closed completely.

do the mod like i said and blip the throttle JUST A TOUCH the throttle and watch the plunger, even through it may be SLIGHTLY open at idlke.. as son as you get ANY throttle (hence LONG before building boost) the bov will slam shut, because when you give ANY thrtotle the VAC will decrease and the spring will shut the BOV.. for instance if your pulling 20psi of VAC at idle, and did it as i specified, anything LESS than 20psi of vac will resulet in the BOV closing totally, and any amount of throttle will result in this.

Nope. The pressure in the manifold AND the spring hold the BOV shut, you need both. You cruch a 1g MOV to stay closed at idle, and to keep it from leaking, and to keep it closed at part throttle.


the spring makes up about prolly less than 30% of the holding force, most people thing the spring is what keeps it shut, and thus have their BOVs (if adjustable) way tighter than ever will be needed.

this adjustment i did with the type S i set the spring where it can BALRY hold it closed (small small amount open) at idle, yet it will hold 25psi no probs.. the spring is set VERY loose (i was waiting for the screw fall out )

I cranked it down a bit (4 threads showing) to prevent the leak and now it runs like a champ

It will flutter ALOT MORE if it is not set properly, having it too tight causes it op open.. then be pushed back shut by the spring and the pressure spike... opens again.. etc.

the spring SHOULD NOT be enough to hold your BOV shut at boost, NO WAY, that is not how its designed to work, the vaccum/boost is supposed to be what regulates your bov, the spring is just there to give a LITTLE extra help and keep it shut during idle..

mine used to fultter BAD untill i did it this way, now it doesent AT ALL, and like i said, set the spring so it JUST BARLY offsets the vac and watch the plunger as you blip the throttle.. at just SLIGHT throttle it will slam shut, and it will stay that way untill you return to vac or you need to vent some boost.

 

[RuBiCaNT5X]

Wobble - what is your vac at idle? What is your vac after getting on the throttle and then letting off completely? My vac at idle is around 15 hg and after getting off the throttle, it's 20 hg or so. I've heard the vac is a tad different on an automatic than it would be on a 5 speed.. Obviously I need to make an adjustment because that did seem a tad low on the vac end of things..

 

[kpt4321]

Originally posted by Wobble true.. sort of, but the added pressure of the spring (= to about 16 psi minimum will more than offset this)

Not sure what you mean by "sort of." It's definately true.

This s just something not a lot of people understand. It's also a situation where you have to rely on the spring to hold the BOV shut.

the spring makes up about prolly less than 30% of the holding force, most people thing the spring is what keeps it shut, and thus have their BOVs (if adjustable) way tighter than ever will be needed.

What percentage of the holding force the spring makes up is totally dependant on the pressure differential from the manifold to the IC pipe, and the total boost level.

If you have your BOV set to stay closed up to 18 inHg, then you have close to 10 pounds of spring force. That means at 20 psi, the spring *could* be doing half the work. In most cases it doesn't have to because the boost is there, but the point is, the spring has a strength of half the boost.

 

[Wobble]

Originally posted by RuBiCaNT5X
Wobble - what is your vac at idle? What is your vac after getting on the throttle and then letting off completely? My vac at idle is around 15 hg and after getting off the throttle, it's 20 hg or so. I've heard the vac is a tad different on an automatic than it would be on a 5 speed.. Obviously I need to make an adjustment because that did seem a tad low on the vac end of things..

at idle im at 20, after letting off gas.. i drop to 26 or so, yea, i *think* the auto is a bit different, but not 100% sure, vac does seem a little low though, but what mods do you have? cams will lower vac at idle, and so will lots of other things.

 

[RuBiCaNT5X]

Originally posted by Wobble
at idle im at 20, after letting off gas.. i drop to 26 or so, yea, i *think* the auto is a bit different, but not 100% sure, vac does seem a little low though, but what mods do you have? cams will lower vac at idle, and so will lots of other things.

3" O2 Elim Turboback
Ported S 16G
All hard IC piping
Greddy Type-S
190lph
MBC @ 15psi
2.75" Intake

 

[1fast97gsx]

mines about 17 at idle... 5 speed gsx

 

[Sephroth57]

17 vac at idle on a 2g isnt good. you should have at least 20 you probably have a small leak somewhere. try doing the leakdown test i bet youll find something leaking

 

[djpast]

17 vac at idle on a 2g isnt good. you should have at least 20 you probably have a small leak somewhere. try doing the leakdown test i bet youll find something leaking

actually, add about 1 inch/mercury for each 1000 miles you are above sea level. for example: when i lived in klamath falls (elevation:~4800 ft above sea level), my vac was at 15-16. In san fran (elevation: 30 ft above sealevel) my vac is at 21-22. In portland (elevation: ~200 ft above sea level) my vac is 20-21.

 

[Groomz]

Originally posted by kpt4321



What percentage of the holding force the spring makes up is totally dependant on the pressure differential from the manifold to the IC pipe, and the total boost level.

If you have your BOV set to stay closed up to 18 inHg, then you have close to 10 pounds of spring force. That means at 20 psi, the spring *could* be doing half the work. In most cases it doesn't have to because the boost is there, but the point is, the spring has a strength of half the boost.

The force the spring exerts is not dependent on the boost pressure. You change the "nut" ( by threading it down or up ) to change the overall height which effects the pressure the spring applies. This is why Wobble recommends adjusting the "nut" to change the amount of pressure the spring delivers at idle. A spring in any atmosphere will deliver the same pressure unless physically affected by an outside force. If springs depended on the ambient atmosphere for the amount of force or pressure they could deliver, than springs would be useless in space, or on a vehicle that changes altitudes as the spring rate would constantly be changing. Springs on earth deliver the same pressure that springs in space do. Period.

The amount of force exerted to keep the blow-off valve shut is dependent on the amount of pressure being applied to it. That pressure comes from the intake manifold which would have the presence of pressure under boost, which would be transfered through tubing to the blow-off valve, providing the necessary pressure to maintain a tight seal.

Boost pressure keeps the blow-off valve shut, not springs tension. This is why there is a tube connecting the blow-off valve to the intake manifold ( which would have either boost or vacuum present inside it ). The spring is present to work against the vacuum whither it is present at idle or cruise. You can overshoot the problem by delivering too much spring tension, but it would increase wear on the mechanism and would be completely unnecessary to having a properly functioning blow-off valve.

Disconnect your line from the blow-off valve to the intake manifold and see what happens under boost or vacuum. You may not like it.

BTW: Excellent article Wobble, very helpful for those who have the Type-S blow-off valve. Maybe this thread should be in the Tech Articles section?

 

[Wobble]

Thanks

It surpises me how LITTLE info there is out there on properly adjusting a BOV like this.. it seems 99% of people have it WAY too tight because they believe the spring keeps the bov shut. I can only pity the turbo..

 

[kpt4321]

Originally posted by Groomz The force the spring exerts is not dependent on the boost pressure. You change the "nut" ( by threading it down or up ) to change the overall height which effects the pressure the spring applies. This is why Wobble recommends adjusting the "nut" to change the amount of pressure the spring delivers at idle. A spring in any atmosphere will deliver the same pressure unless physically affected by an outside force. If springs depended on the ambient atmosphere for the amount of force or pressure they could deliver, than springs would be useless in space, or on a vehicle that changes altitudes as the spring rate would constantly be changing. Springs on earth deliver the same pressure that springs in space do. Period.

Huh? I don't even understand what you're trying to prove. Or what you'r arguing with.

Boost pressure keeps the blow-off valve shut, not springs tension.

At WOT, the total force on the top of the BOV (boost + spring) is greater than the total force on the bottom (boost). How can you say that the boost is doing all of the work, when the spring is doing some of it too?

As a matter of fact, if you didn't have the spring, your BOV would leak at wide open throttle. I guarantee it. In fact, it would leak all of the time.

That means that the spring HAS to be doing some of the work.

The spring is present to work against the vacuum whither it is present at idle or cruise.

The spring is present to exert a force in the "closed" direction, regardless of the condition of the pressure in the source line.

You can overshoot the problem by delivering too much spring tension, but it would increase wear on the mechanism and would be completely unnecessary to having a properly functioning blow-off valve.

Not to mention it would increase compressor surge and stall.

Disconnect your line from the blow-off valve to the intake manifold and see what happens under boost or vacuum. You may not like it.

Without the source line, the BOV will stay closed at idle, and closed at cruise. It will open at part throttle, and at WOT.

 

[Wobble]

... and go WOOTCHAWOOTCHAWOOTCHAWOOTCH!!!!

 

[Coldandafraid]

I like your reasoning wobble... now... how do I go about adjusting my hks ssq (pull type) bov? Do the opposite?

 

[DSMJim]

I cranked the shit out of my type-s so that my car compressor surges for anything under 2-3 psi of boost. I would rather it be super tight then risk it being open.

At the track I crank the bi*** right down so it's as tight as it can go. NO need for a BOV when your racing.

 

[Wobble]

wow, i bet your turbo is just delighted with that setup.. yikes

 

[Groomz]

The boost pressure does most ( by most I mean a whole lot ) of the work in keeping the blow-off valve shut under boost. The spring does still provide tension to keep the valve closed, but it is not the primary source keeping the valve shut.

I do not have any hands on experience with the Type-S blow-off valve, but when I upgrade from my 1G blow-off valve, I will be using an HKS SSBOV. The right one.

 

[kpt4321]

Originally posted by Groomz
The boost pressure does most ( by most I mean a whole lot ) of the work in keeping the blow-off valve shut under boost. The spring does still provide tension to keep the valve closed, but it is not the primary source keeping the valve shut.

Under vacuum, the spring is the only thing holding the BOV shut.

Under part throttle boost, the spring is doing ALL of the work in holding the BOV shut, and sometime even that isn't enough.

Under WOT, there is more pressure on the top of the BOV then on the bottom, so how can you say which components on the top do "more work" than others do? You can't.

 

[nineD5_GS-T]

Originally posted by Groomz


I do not have any hands on experience with the Type-S blow-off valve, but when I upgrade from my 1G blow-off valve, I will be using an HKS SSBOV. The right one.

The right one would be a Tial BOV.

 

[Sephroth57]

Originally posted by nineD5_GS-T
The right one would be a Tial BOV.

I agree, tial is the shiznit

 

[RuBiCaNT5X]

The Tial isn't a recirculating BOV, correct?

 

[kpt4321]

Correct.

 

[Wobble]

then unless you have a VPC or something, its the WRONG one, i know i know... it sounds cool.. bla bla.. but it still hurts performance.