Stopping Your BOV From Leaking - A How To

[Black33]

Increasing the size of the bypass hole will cause less vac on the back side of the piston and also enable higher boost to be held. But cause more leakage....

exactly what I was thinking, so if we are to block this hole to allow for better response and boost coming on earlier - what boost pressure do you think the BOV spring alone can hold (ie with no pressure on the backside due to the leak helping to keep the valve shut)?????

[Jay95R33]

what boost pressure do you think the BOV spring alone can hold (ie with no pressure on the backside due to the leak helping to keep the valve shut)?????

Going from Freebaggin's results that are posted earlier on in this thread, and also seeing my car on the dyno at 12psi, I'd say they will hold boost upto 1 bar with no problems.

I was going to do the full on mod that Boostd has done, but in my particular case I don't think it's worth the effort. It probably is if your running higher boost, but at 12psi I'm not sure if it would be that much of a benefit. The jerking/surging isn't a problem in my car. It happens maybe once or twice in a fortnight, so it's really no issue.

J

[sweetr33]

Another tip, i disconnected the vacuum line going from the manifold to the BOV and blocked off that vacuum line. Holy moly, the noise that comes from the pod when excess pressure is released is aweseme, its a 'Flutter'. Should try it. It sounds amazing

[Freebaggin]

exactly what I was thinking, so if we are to block this hole to allow for better response and boost coming on earlier - what boost pressure do you think the BOV spring alone can hold (ie with no pressure on the backside due to the leak helping to keep the valve shut)?????

Black33, if you take a look at the setup you'll see that the line from the manifold to the top of the BOV is used to hold the BOV closed under BOOST. The pressure is imposed on the diaphram in the BOV works in conjunction with the sping.

The spring is there to keep it closed under vacuum and therefore no leaks as well.

The line you are blocking off feeds onto the diaphram but in the opposite direction to the manifold line and OPENS the BOV under boost (maybe above 12psi).

So there is no risk of the BOV opening under boost, I spose that's the whole point of doing it, no leaking under boost and therefore let the boost controller do the controlling, not the BOV.

Increasing the size of the bypass hole will cause less vac on the back side of the piston and also enable higher boost to be held. But cause more leakage....

I disagree because the hole feeds pressure on the underside of the diaphram.

[EnricoPalazzo]

Hmm interesting. I blocked off the hole with a small metal plate i made to fit. It does feel like it jerks sometimes. Im not sure thou. I used to have a HKS bov, but got rid of it cos of the situation on defects currently in sa.

[RB30-POWER]

Don't mean to dig up an old thread.

But i am going to use a factory bov on a motor i am building at the moment and i wanted to try and find what this hole does, that a few people have blocked.

I ripped one apart to see whats what in there.

From looking at it and testing it.

The hole on the back of the BOV where its sits on the crossover travels through into the diaphram part of the BOV.

From what i can see, this will either help to open the BOV with less boost/pressure or to make it open more smoothly. Smoother operation.

I don't see anyway that this would leak back into the piping that returns to the air flow meter ducting. The hole isn't linked to that section of the BOV.

It only seems to help the valve open easier, you not only have the pressurised pushing on the BOV piston itself in the cross over, but it would be pushing directly on the diaphram part of the valve. And obviously you will have intake manifold pressure or vacuum on the other side from the plenum to either equalize or help open the valve.

Looking at this, i will be blocking it up, but only because i want to see if it can hold more boost sucessfully.

Have a look and see what you think.

[R31 POWER]

Try this mod.When we were fitting the RB20 motor into the Silo the chain holding the motor was resting on the top of the bov wich crushed the side abit.

Comparing with a mates other RB20 bov we found out that my bov had alot more spring tension and it was hard to push the piston.So maybe bash the top to give it more tension

[RB30-POWER]

What you just said makes sense, as technically you are compressing the spring, much like turning the knob on an aftermarket valve. Bit dodge though

[Dantay]

Hey guys, i'm gonna do this mod but i would like to see the pic's before i jump into it because i'm not 100% on what to do. here.

thanks guys!

[SECURITY]

Hey guys, i'm gonna do this mod but i would like to see the pic's before i jump into it because i'm not 100% on what to do. here.

thanks guys!

http://www.thedodgegarage.com/turbo_bov_mod.html

[Dantay]

yeh i saw that, but i was after the sorta "dodge" way ie just plugging the hole as opposed to drilling into the mech.

[SECURITY]

[R338OY]

I'm always skeptical of backyard mods, but this one is OK.

As long at whatever you fill the hole with is secure it gives low RPM boost a little more punch. Response is better.

Also on partial throttle the boost gauge needle holds, rather than always leaking out and giving a flat feeling- meaning you don't need to hit it if you want to make back that charge.

Partial throttle isn't as smooth with this mod, for obvious reasons, but it's not very noticable. I think the benefit of plugging what is basically a boost leak outweighs a tiny negative.

Great little mod for the plumb back crew

[benl1981]

Just did this. Blocked up the small hole with some gasket maker (built it up slightly so when you tighten the 2 bolts is squashes in and is secure). It seems to be a lot more responsive. Suprised a few post back somebody that pulled a BOV appart believed that small hole doesn't plumb back and isn't effectively a "leak".

I'm sure it's boosting quicker and part throttle in 4th or 3rd comes onto boost quicker and feels less flat.

[benl1981]

It's only a small amount of air, however it would lean out the air flow slightly since you are no longer leaking that small amount back into the turbo inlet I.e if your car was tuned with the bleed hole open then you block it after the tune. I guess it would only be a very small amount. However, the air is coming back in after the AFM though...??

Makes a more agressive sound with it blocked. It's wierd how Tomei tell you to do this when you intall new camshafts. They probably want you to think wow the cams made a huge difference when in fact it's probably the blocking off this hole in the BOV that improves the response the most.

has there been any negative side effects with this mod?

Edited September 27, 2009 by benl1981

[35NIK]

ive had many problems running a turbosmart plumbback in my R34 with it bogging down under slight boost.

So ill give this mod a try, also I heard if you crush your stock bov in a vice alittlebit, it will make the spring tighter which will make it handle more boost.

im going to give both a try.

[T04GTR]

and tis mod to the oe bov has done what on the dyno?

[lachlanw]

the hole is there because the factory bov is like a delta gate waste gate . it has a valve on a seat . not like bov that has a piston . the hole in it is there so boost in the j pipe (side of bov diaphram)combined with vacuum (on the top of bov) will fully open the bov . blocking this hole means that as soon as the bov valve lifts of the seat a lil bit all the air ruches past it and it doesnt open fully .

[lachlanw]

You basically have 4 forces acting on the BOV.

-Pressure or vacuum on the top of the diaphram

-Pressure on the bottom of the diaphram via that lower port

-Pressure on the underside of the valve itself

-Spring pressure on the top of the diaphram

The combination of these forces is what determines the bahavior of the BOV. I'm trying to think of a short way to describe all of the typical situations, but I don't think there is one. The key point though is that the valve and diaphram are not the same size. The force on each is different at the same pressure since force = pressure times area. The diaphram is always larger than the valve, giving it more control over the BOVs actions than the valve. If the diaphram is twice the size of the valve, and there is 20 psi of boost (so 20 psi on the top of the diaphpram and 20 psi on the bottom of the valve), the valve will stay shut since there is double the force holding it shut. Also add in the spring pressure trying to hold it shut.

The problem is that the lower port allows the same boost pressure to reach the bottom the of the diaphram trying to open the valve. It effectively cancels the pressure on the top port, leaving only the spring pressure to hold the valve shut. If this was a static system it would still stay closed, but pressure in the IC piping (lower port) and in the manifold (upper port) is always varying, and at different rates. So the BOV tend to open at some pressure differential.

The purpose of the lower port, also called the fast release port, is to open the BOV more quickly when the throttle plate closes. Vacuum will build up on the top of the diaphram pulling the valve up, and pressure will spike in the UICP pushing on the valve (remember that is is ~half the size of the diaphram) AND on the lower part of the diaphram, opening it quickly. And in fact, putting atmosphere on that lower port will slow down the valves reaction time, and the valve/turbo become very noisy. And I agree that you would never want to cap off the bottom of the diaphram, as it would hinder movement of the diaphram.

[benl1981]

hmm

So by blocking that hole I have probably hindered the valve opening fully.

I'm sure the boost is building faster with it blocked and part throttle is so much more effortless. So that hole must have actually leak it back into the inlet?

I guess I'm not using it the way it's designed to be.

It mustn't be too bad if Tomei put it on their instructions for installation of Poncams?