BOV Crushing Limit

[Echo5Zulu]

After reading the articles on modding the bov I still have a couple questions. If I decide to crush my 1gen bov instead of the dodge mod what is the limit you can crush it to while using a vacuum gage? I want to run about 20psi so should/could I crush it to 24 or 25psi? What is it at if I just crush it to where the little nipple touches like everyone says to?
Thanks.

 

[fourreGsixty3]

1G BOVs can hold around 22-23psi unmodded. When crushing don't crush it more then 1/8".

 

[Boosted98gsx]

use a penny and put it between the nipple and the ledge underneath. Crush it till the penny is held, remove penny, VOILA!

 

[Steve93Talon]

Crushing is obsolete. The "correct" way to mod a BOV is to do the Dodge/Gus/Dejon mod. That is, tapping and threading the hole on the underside next to the valve and putting a set screw and drilling a small relief hole on the side where that passage leads to the underside of the diaphragm.

 

[Echo5Zulu]

1G BOVs can hold around 22-23psi unmodded. When crushing don't crush it more then 1/8".

Not to call you a liar; but is that what yours tested at? Ive allways heard they start opening around 15lbs. Maybe I'll have to get the vacuum tester and test it first. Or maybe Im missunderstanding you. Do you mean before or after crushing?

As for the last poster; about the penny trick; do you know what it will hold once modded with the penny trick? Maybe I'll just do the garage mod, I just thought crushing it would be easier and quicker, but if I cant reliably get it to hold 24-25 and I know the garage mod holds 30lbs maybe I better take the time and do it right.

Thanks.

 

[xveganxcowboyx]

Mine was crushed to -20 on the vacuum gauge. Started leaking at 17 psi. I crushed it to -21, but haven't retested it yet. I've decided the dodge garage method is the proper one for high boost.

 

[bling5tatus]

yep agreed, I would not crush a perfectly good bov, in fact I have a tial bov right now that is not recirc'd, but I bought the car like that. I am looking to buy a 1g bov so I can do the dodge garage modification to it.

 

[damnslowtsi]

Mine is crushed to about 18-19 in/hg using a vacuum pump with a gauge and holds to at least 25#s. Modding it the right way is of course better but this is fast and free. You can always pick another one up from a junk yard to be modded properly.

 

[Echo5Zulu]

Mine is crushed to about 18-19 in/hg using a vacuum pump with a gauge and holds to at least 25#s. Modding it the right way is of course better but this is fast and free. You can always pick another one up from a junk yard to be modded properly.

So when you crushed yours you tested it at it opened around 19? How do you know its holding at 25lbs; boost leak tester?? Or did you crush it to where the nipple just hits and then tested it? Or maybe the penny trick?

Im going to crush mine tonight and if I dont like it I'll just pick up a used one somewhere and do the garage mod way (wich Im still not totally convinced on). BOV's are cheap luckily.

 

[xveganxcowboyx]

Read this write-up on the dodge garage mod. It's a lot clearer than the original site.

http://www.dsmtuners.com/forums/showthread.php?t=220909

 

[Echo5Zulu]

Read this write-up on the dodge garage mod. It's a lot clearer than the original site.

http://www.dsmtuners.com/forums/showthread.php?t=220909

Read that one allready but thanks for the thought.

 

[WatchItExplode]

One thing about the Dodge Garage mod I'm curious about: does the BOV still open effectively if you let off the throttle at low boost? For example you're cruising and decide to shift when you've only built up 5 psi or so, will the BOV still open like it would from the factory?

 

[damnslowtsi]

So when you crushed yours you tested it at it opened around 19? How do you know its holding at 25lbs; boost leak tester?? Or did you crush it to where the nipple just hits and then tested it? Or maybe the penny trick?

Im going to crush mine tonight and if I dont like it I'll just pick up a used one somewhere and do the garage mod way (wich Im still not totally convinced on). BOV's are cheap luckily.

Yes, the valve starts opening around 18" of vacuum or so and yes it holds to that psi using a boost leak tester. I 've just learned about the penny trick myself ha-ha. The downside of crushed BOVs is that they may bypass a bit less air than the modded ones since the spring tension is increased and the valve travels less under same vacuum obstructing airflow more. I never had a problem back in the 16g days but now it occasionally makes the car surge when let off.

 

[Echo5Zulu]

Just got finished crushing mine. Tested it uncrushed and it started opening at 15. I crushed it to where the nipple just starts touching the ledge below and it now holds to 20. Put it all together and drove around town and back home from my dads shop and all seems well. So looks like I should be good to start turning up the boost towards 20.

 

[oldman]

One thing about the Dodge Garage mod I'm curious about: does the BOV still open effectively if you let off the throttle at low boost? For example you're cruising and decide to shift when you've only built up 5 psi or so, will the BOV still open like it would from the factory?

I run it in quick release mode, basically unmodded, until I go to the track, mine flatters otherwise in low boost.

 

[Boosted98gsx]

If you have the mod done when you are running around in anything but WOT full boost mode, you will surge during a low boost blow off.

 

[Echo5Zulu]

If you have the mod done when you are running around in anything but WOT full boost mode, you will surge during a low boost blow off.

Thats what I was thinking when I read about the Garage mod. Im still not sure about that one.

On a side note on the bov theory. At wot the bov even stock should hold high boost since pressure on both sides of the throttle body should be equal. Only when the pressure on the intake side of the throttle body gets too low or goes to vacuum should the valve open. Correct?? So modding and raising the bov threshold should just be for helping in mid to low boosting right?

 

[oldman]

On a side note on the bov theory. At wot the bov even stock should hold high boost since pressure on both sides of the throttle body should be equal. Only when the pressure on the intake side of the throttle body gets too low or goes to vacuum should the valve open. Correct?? So modding and raising the bov threshold should just be for helping in mid to low boosting right?

It doesn't work like that, much like a wastegate trying to hold back exhaust pressure pushing against the surface of the valve, there is a breaking point where the spring pressure is physically overcome, that breaking point is usually 2x the spring pressure. In the case of the 1G BOV with 8psi spring, the valve will start to leak at about 16ish PSI, the purpose of crushing and the DG mod is to increase the spring pressure therefore holding more pressure under WOT.

 

[Echo5Zulu]

It doesn't work like that, much like a wastegate trying to hold back exhaust pressure pushing against the surface of the valve, there is a breaking point where the spring pressure is physically overcome, that breaking point is usually 2x the spring pressure. In the case of the 1G BOV with 8psi spring, the valve will start to leak at about 16ish PSI, the purpose of crushing and the DG mod is to increase the spring pressure therefore holding more pressure under WOT.

Maybe I missunderstood the article. I was thinking when the throttle plate is open your getting boost in the line going to the top nipple in the tophat and when the plate is closed it turns to a vacuum which then helps open the valve quickly to prevent system damage. Made sense to me since thats how its piped but maybe I'm wrong.

While Ive got your attention what is your opinion on the garage mod? Ive read it over multiple times but Im still not convinced its the safest/best way to go. What is your theory on how the garage mod works in laymans terms?

Thanks.

 

[oldman]

Maybe I missunderstood the article. I was thinking when the throttle plate is open your getting boost in the line going to the top nipple in the tophat and when the plate is closed it turns to a vacuum which then helps open the valve quickly to prevent system damage. Made sense to me since thats how its piped but maybe I'm wrong.

That is correct and no where did I dispute that. There are 4 different forces at work under WOT,

1. The spring pressure pushing down on the valve.

2. The top chamber of the BOV pushing down on the valve adding to the spring pressure.

3. The bottom chamber of the BOV lifting the valve reducing the spring pressure.

4. The intake pressure in the UICP pushing up against the valve surface.

In a stock/unmodded 1G BOV under WOT, both the top and bottom chambers recieves the same amount of pressure therefore you're left with spring pressure alone to hold back the intake pressure in the UICP, 1 vs 4, and like I mentioned above, the valve gets overcome at about 2x the spring pressure, in this case 8psi spring pressure will hold about 16ish psi of intake pressure. Now Let's talk about what crushing and DG does.

1. Crushing, it's pretty straight forward, you're shortening the length of the spring resulting in heavier spring pressure.

2. DG mod, you're blocking off the access route to the UICP from the bottom chamber therefore you now have 1+2 vs 4. This can be reversed by connecting the weld on fitting (to bottom chamber) to a pre-TB pressure source AKA "quick release mode".

While Ive got your attention what is your opinion on the garage mod? Ive read it over multiple times but Im still not convinced its the safest/best way to go. What is your theory on how the garage mod works in laymans terms?

The risk in crushing and DG modding, as well as tightening the adjustment rod on an adjustable aftermarket BOV are the same, the difficulty in opening the valve after letting off under low boost situations. Let's break down the blow off functions of the virgin 1G BOV,

1. Spring pressure pushing down on the valve.

2. Top chamber in vacuum pulling up on the valve.

3. Bottom chamber pushing up on the valve.

4. Intake pressure pushing up on the valve.

1 vs. 2+3+4

As you can see with an 8psi spring on the stock 1G bov while the car is pulling -18 inHG (-9psi) of vacuum, opening the valve is never a problem under any circumstances since #2 > #1. With that said, this is also the reason why a 1G BOV stays open at idle.

Now for argument sake, let's say crushing or adjusting spring pressure increased the spring pressure to 14psi, let's calculate the minimum intake pressure (X) needed to open the valve assuming -18 inHG of vacuum.

spring pressure = #2 vacuum (9psi) + #3 intake pressure (X) + #4 intake pressure (X)/2

14psi = 9 + X + X/2

5 = 3X/2

X=3.3psi

This tells us that if the 1G bov is crushed to 14psi, or an after market BOV is adjusted to 14psi, any blow off under 3.3 psi will result in a closed BOV.

DG modding is a better method because it doesn't have this problem in most cases, exception (like in my case) being aftermarket cams pulling less than -16 in HG, because it doesn't directly increase the spring pressure, it simply removes #3 from the equation.

 

[Echo5Zulu]

Thank you for taking the time and going through all of that. I really like how you layed it out in your description. The conclusionary paragraph really sums up the Garage mod by saying it removes the bottom chamber from pushing up on the valve.

Ive allready crushed mine but if I have problems I can allways pick up another used one for cheap. What sort of problems do you think I may have, may I ask? Just the low boost blow off as stated in your description? I crushed it to hold 20hg of vacuum using a mity vac. Ive heard of a lot of guys running them crushed so it should be fine.

Hopefully this thread will help clear things up for others as much as it did for me.

Thanks.

 

[oldman]

What sort of problems do you think I may have, may I ask? Just the low boost blow off as stated in your description?

That is about it, listen for turkey calls when blowing off under part throttle boost.

 

[Echo5Zulu]

That is about it, listen for turkey calls when blowing off under part throttle boost.

Ha Turkey calls! Maybe I can use it to lure turkeys in during turkey season? Just kidding. Anyway it shouldnt cause any damage would it?

 

[oldman]

Anyway it shouldnt cause any damage would it?

Yes it can, BOV not openning, openning fully or openning on time (hence BOV flatter/turkey call) will force pressure to flow backwards against your compressor wheel.

 

[Echo5Zulu]

Yes it can, BOV not openning, openning fully or openning on time (hence BOV flatter/turkey call) will force pressure to flow backwards against your compressor wheel.

I dont like the sound of that. If Im not getting the turkey call it should be fine right? Or is it still backflowing just not hard enough to hear? How hard is this on the turbo bearings?

Just so I have my head straight; in the dg mod your basically plumbed the same as before but your blocking the little port on the bottom side and then drilling a hole to vent it to the atmosphere instead correct? Am I correct in saying that it also doesnt open as quick when its modded unless you hook up the "quick release" mode? So unless your in "quick release" mode it probably acts similar to the crushed bov.

Sorry about all the questions I enjoy learning the theories behind everything and how it all works. Thanks.