General Please help me fix my compressor surge!

[silentsnow31802]

Here is a 3rd gear pull log I made a few days ago and sent to the tuner.

 

[DSMPT]

There is only 1 port.

Try to replace the spring to soften the valve and see what happen.

You said the BOV is opening after WOT or accelerating aggressively and it surges after partial throttle while cruising. Then the BOV is operating as it should. It seems you just don't have enough vacuum against the BOV spring after partial throttle.
What you described is exactly what would happen if you keep tightening the adjustment bolt to stiffen the valve on an adjustable BOV such as GReddy BOVs.

In my 1g, I have about 10~12 inHg at idle and around 24 inHg after WOT, so after partial throttle is somewhere in between those numbers. And I have a BOV spring for 8~16 inHg range of intake manifold vacuum.
Again, your BOV may be too stiff. Try to soften it. It seems that you are thinking that the boost pressure would push open the valve if you soften the valve, but no, it won't, the boost pressure won't open the valve as long as if the BOV is in good working condition. What would happen when you soften too much, you would start to experience that the idle gets unstable or sometimes the engine gets stalled. In that case go with stiffer spring and you will be fine.

 

[Justin DuBois]

Here is a 3rd gear pull log I made a few days ago and sent to the tuner.

You must be logged in to view this image or video.

Your boost control is interesting. Looks like you are holding back the compressor until you get to 4600rpm.
Biggest improvement you could make is to increase the timing in the middle of your pull.
You could improve your Wideband to AFR target alignment.

 

[silentsnow31802]

Try to replace the spring to soften the valve and see what happen.

You said the BOV is opening after WOT or accelerating aggressively and it surges after partial throttle while cruising. Then the BOV is operating as it should. It seems you just don't have enough vacuum against the BOV spring after partial throttle.
What you described is exactly what would happen if you keep tightening the adjustment bolt to stiffen the valve on an adjustable BOV such as GReddy BOVs.

In my 1g, I have about 10~12 inHg at idle and around 24 inHg after WOT, so after partial throttle is somewhere in between those numbers. And I have a BOV spring for 8~16 inHg range of intake manifold vacuum.
Again, your BOV may be too stiff. Try to soften it. It seems that you are thinking that the boost pressure would push open the valve if you soften the valve, but no, it won't, the boost pressure won't open the valve as long as if the BOV is in good working condition. What would happen when you soften too much, you would start to experience that the idle gets unstable or sometimes the engine gets stalled. In that case go with stiffer spring and you will be fine.

I need to get a camera in the in the engine bay and see what the BOV is actually doing VS what it sounds like it's doing.

The softer spring that came with it doesn't make any difference. Are you saying go softer than that? The original spring was rated for -8 to -13 in/hg but would cause the BOV to be open at idle.

I'm also going to plumb my boost gauge into the same line as the fuel regulator temporarily so it will register vacuum at idle. The P port on my throttle body is on the charge pipe side not the manifold side so when the throttle is closed it shows 0.

You must be logged in to view this image or video.

Your boost control is interesting. Looks like you are holding back the compressor until you get to 4600rpm.
Biggest improvement you could make is to increase the timing in the middle of your pull.
You could improve your Wideband to AFR target alignment.

We're still in the middle of tuning for E85 so things may change as time goes on. I'm hoping what you suggest will happen once we get into turning things up further.

 

[DSMPT]

The softer spring that came with it doesn't make any difference. Are you saying go softer than that?

I am saying softer than now according to what you described. In case if the BOV doesn't open well and if that is causing the issue you are talking about, then you should soften the valve, not stiffen. That's what I am saying.

The original spring was rated for -8 to -13 in/hg but would cause the BOV to be open at idle.

How did you confirm that the BOV is/was open at idle with the original spring? Did you physically confirm that by yourself or just a guesstimation? If you haven't confirmed it yet, I would put back the original spring that came with the BOV. At least it would probably work better than the higher pressure spring and it's more friendly to the turbo.

 

[pauleyman]

I need to get a camera in the in the engine bay and see what the BOV is actually doing VS what it sounds like it's doing.

The softer spring that came with it doesn't make any difference. Are you saying go softer than that? The original spring was rated for -8 to -13 in/hg but would cause the BOV to be open at idle.

It's supposed to be open at idle. That is why we preach to have a bov recirculate on a maf setup because it's open at idle.

I'm also going to plumb my boost gauge into the same line as the fuel regulator temporarily so it will register vacuum at idle. The P port on my throttle body is on the charge pipe side not the manifold side so when the throttle is closed it shows 0.



We're still in the middle of tuning for E85 so things may change as time goes on. I'm hoping what you suggest will happen once we get into turning things up further.

 

[Justin DuBois]

It's supposed to be open at idle. That is why we preach to have a bov recirculate on a maf setup because it's open at idle.

Yeah - the recirc is required on MAF. It's good he is running SD, cause that is required for this kind of BOV that vents to atmosphere. IMO, this BOV should be leaking or nearly leaking at idle. You need the BOV to open smoothly at part throttle.

 

[pauleyman]

Yeah - the recirc is required on MAF. It's good he is running SD, cause that is required for this kind of BOV that vents to atmosphere. IMO, this BOV should be leaking or nearly leaking at idle. You need the BOV to open smoothly at part throttle.

Yup. Back up my point. You shouldn't run a maf with this type of BOV because it's open to atmosphere. Op has it right with speed density but if bov isn't open....well it should be. Might even need a spring lighter than 6lbs if engine doesn't produce much vacuum.

 

[Justin DuBois]

Yup. Back up my point. You shouldn't run a maf with this type of BOV because it's open to atmosphere. Op has it right with speed density but if bov isn't open....well it should be. Might even need a spring lighter than 6lbs if engine doesn't produce much vacuum.

Springs man... the springs in the various valve controls (BOV and WG) are really starting to show me their limitations. I'm now in the camp that I want pneumatic ports above and below the actuator diaphragms so I can manage the valves better.
- I need one of these.

I'm also in the reverse BOV config camp - a design that holds itself shut. I need to find one of these.

 

[pauleyman]

Springs man... the springs in the various valve controls (BOV and WG) are really starting to show me their limitations. I'm now in the camp that I want pneumatic ports above and below the actuator diaphragms so I can manage the valves better.
- I need one of these.

I'm also in the reverse BOV config camp - a design that holds itself shut. I need to find one of these.

As I'm not in the high boost camp I really don't understand a limit on bov. Under boost you have boost top and bottom so the only difference is the spring and it doesn't take much. Shut throttle and then you have vacuum top, boost bottom, valve opens and bleeds off. If there is something I'm not understanding elaborate please.
The spring just needs to be sized appropriately so the valve opens under whatever vacuum provided. Only gotcha I see is the boost top and boost bottom might not be exactly equal nor will they arrive at same time

 

[silentsnow31802]

I am saying softer than now according to what you described. In case if the BOV doesn't open well and if that is causing the issue you are talking about, then you should soften the valve, not stiffen. That's what I am saying.


How did you confirm that the BOV is/was open at idle with the original spring? Did you physically confirm that by yourself or just a guesstimation? If you haven't confirmed it yet, I would put back the original spring that came with the BOV. At least it would probably work better than the higher pressure spring and it's more friendly to the turbo.

I physically looked at the BOV at idle and it was wide open.

It's supposed to be open at idle. That is why we preach to have a bov recirculate on a maf setup because it's open at idle.

I dont think its supposed to be open at idle. Thats the job of the spring. To overcome the vacuum. I thought the point of the BOV recirculating was so that the already metered air it blows out during a blow off goes back into the engine so it doesn't stall or stutter when boost if bled off?

Yeah - the recirc is required on MAF. It's good he is running SD, cause that is required for this kind of BOV that vents to atmosphere. IMO, this BOV should be leaking or nearly leaking at idle. You need the BOV to open smoothly at part throttle.

I agree with nearly leaking at idle, but not leaking.

As I'm not in the high boost camp I really don't understand a limit on bov. Under boost you have boost top and bottom so the only difference is the spring and it doesn't take much. Shut throttle and then you have vacuum top, boost bottom, valve opens and bleeds off. If there is something I'm not understanding elaborate please.
The spring just needs to be sized appropriately so the valve opens under whatever vacuum provided. Only gotcha I see is the boost top and boost bottom might not be exactly equal nor will they arrive at same time

Im terrible at explaining things but from my inderstanding...
The spring pressure is there to hold the BOV closed at idle, while the manifold is under vacuum and the charge pipes have 0 pressure in them.
During boost the pressure on the vacuum line and the pipe side of the BOV is the same so the valve is naturally held closed because there is no pressure differential to overcome the valve/spring.
When you let off the throttle the throttle body snaps closed and now you have boost in the piping but not the intake manifold causing a big differential on each side of the BOV. Assuming this is more than the spring can hold the valve will open and vent off the pressure until it gets to a point where the spring is strong enough to close it again.



But! I plumbed my boost gauge into the manifold not the throttle body so I can now view an actual vacuum value at idle. I get -17 to -18 in/hg.
According to this chart I need the Plain spring which is what is currently in the car.
I have the Q version of the BOV.
The car originally had a black spring which is why the BOV was open at idle. Too soft.

You must be logged in to view this image or video.

Am I right in assuming I have the correct spring according to this chart?

 

[pauleyman]

I physically looked at the BOV at idle and it was wide open.


I dont think its supposed to be open at idle. Thats the job of the spring. To overcome the vacuum.

incorrect. If you put a hand vacuum on a bov it will be wide open at 20 inches mm. At idle there is no pressure in the charge pipe so the only thing holding the bov closed is the spring. Idle vac easily opens it. That's why we recirculate. If you don't you suck in unmetered air at idle and the car idles poor or dies. Bov is wide open at idle, not just a little bit.

I thought the point of the BOV recirculating was so that the already metered air it blows out during a blow off goes back into the engine so it doesn't stall or stutter when boost if bled off?


I agree with nearly leaking at idle, but not leaking.


Im terrible at explaining things but from my inderstanding...
The spring pressure is there to hold the BOV closed at idle,

Incorrect. The spring is the only thing that holds it closed under boost. Under boost have have pressure below and on top of diaphragm and they're equal (or nearly so). That may not be exactly true on an aftermarket valve depending on design but for sure on a stock valve it is. There is a hole in the charge pipe side to let pressure under the diaphragm. Spring pressures may be greater on aftermarket if they don't have a hole like this. Lookup dodge mod on a stock valve and you can see how it changes behavior with and without the hole. Might explain what I'm talking about.

while the manifold is under vacuum and the charge pipes have 0 pressure in them.
During boost the pressure on the vacuum line and the pipe side of the BOV is the same so the valve is naturally held closed because there is no pressure differential to overcome the valve/spring.
When you let off the throttle the throttle body snaps closed and now you have boost in the piping but not the intake manifold causing a big differential on each side of the BOV. Assuming this is more than the spring can hold the valve will open and vent off the pressure until it gets to a point where the spring is strong enough to close it again.



But! I plumbed my boost gauge into the manifold not the throttle body so I can now view an actual vacuum value at idle. I get -17 to -18 in/hg.

Change the location of the boost gauge tap so you can see it. You may not have as much vacuum as you think.

According to this chart I need the Plain spring which is what is currently in the car.
I have the Q version of the BOV.
The car originally had a black spring which is why the BOV was open at idle. Too soft.

You must be logged in to view this image or video.

Am I right in assuming I have the correct spring according to this chart?

 

[pauleyman]

You just mentioned bov is wide open at idle. It should be functioning under boost. Only think i can think is under part throttle the transition from closed to open is slow. Small vac lines?

 

[curt-s]

The spring is supposed to keep the BOV valve shut or just shut at idle, as mentioned. It's really the only thing keeping it shut at idle because you don't have the same vacuum in your UICP as you do in the manifold -- it's much less. That's why you size the spring, whatever your idle vacuum is. If you use too soft of a spring, the valve will be open under idle and light cruise/slight off throttle.

Unacceptable for MAF, not as bad for SD except it lets unfiltered air in.. but your response will be quicker. If the valve was open at idle, you'd be always drawing in dirty unfiltered air and who knows what else from inside your engine bay all the time.

With your vac, I'd say you're on the money. I ran that same spring on my BV50 when I had stock cams and ~-20.

On decel engine brake, your valve will be wide open because the vac the engine is pulling overcomes the spring with ease.

Too much spring (meant for a vacuum even stronger than yours) and it will keep your valve shut under more conditions but it won't open as fast. Depending on which spring, it may not even open at all... but unlikely because your UICP is likely filled with positive pressure air that will assist in opening it when there's a greater pressure differential between the upper and lower halves.

At idle, it should not be open. If it is, you need a stronger spring.

When you blip the throttle, you'll see it open because your engine vacuum will exceed that the spring is rated for and the vacuum will actually draw the valve open even though your UICP will also be in vacuum. It's all about the pressure differentials.

If you're really worried about heat, mount the camera on the firewall. We won't see as much but it's far from any heat sources.. just try to insulate the camera on rubber or something so that you don't get noise from excessive vibration.

 

[jed344]

I have been using these bov's for i bet over 10 years now. Have used them on a TON of car's and different set ups. When the right spring is picked they function perfectly. Closed at idle, open when needed and will hold anything for boost i have ever seen.

Like explained above they are quite simple in reality. Here is the thing though, if you have a leak or the diaphragm is damaged then this will greatly effect how it reacts.

That same single line that goes to top of the bov is what pulls the top into vacuum to open the bov, but it also adds boost pressure to top of the hat too so it stays closed.
When this scenario shows up the bov may fail to open at correct vacuum and at same time blow open in boost too.

This all assumes this is your issue. I have in the past had the wrong spring in a car so the bov was open at idle but in boost it will stay shut. Just does not pull it's self back closed all the way at idle. What ever boost the car is making is that plus the spring pressure on the top of the bov so that will stay shut as it is more pressure then what is against the bottom of the valve, assuming no leaks.

 

[DSMPT]

I physically looked at the BOV at idle and it was wide open.


I dont think its supposed to be open at idle. Thats the job of the spring. To overcome the vacuum. I thought the point of the BOV recirculating was so that the already metered air it blows out during a blow off goes back into the engine so it doesn't stall or stutter when boost if bled off?


I agree with nearly leaking at idle, but not leaking.


Im terrible at explaining things but from my inderstanding...
The spring pressure is there to hold the BOV closed at idle, while the manifold is under vacuum and the charge pipes have 0 pressure in them.
During boost the pressure on the vacuum line and the pipe side of the BOV is the same so the valve is naturally held closed because there is no pressure differential to overcome the valve/spring.
When you let off the throttle the throttle body snaps closed and now you have boost in the piping but not the intake manifold causing a big differential on each side of the BOV. Assuming this is more than the spring can hold the valve will open and vent off the pressure until it gets to a point where the spring is strong enough to close it again.



But! I plumbed my boost gauge into the manifold not the throttle body so I can now view an actual vacuum value at idle. I get -17 to -18 in/hg.
According to this chart I need the Plain spring which is what is currently in the car.
I have the Q version of the BOV.
The car originally had a black spring which is why the BOV was open at idle. Too soft.

You must be logged in to view this image or video.

Am I right in assuming I have the correct spring according to this chart?

I was feeling a confusion from you. I think I now see the situation, and yes you seem to be misunderstanding at some points. I think you saw that the valve was wide open at idle and that made you hesitating to soften the valve.

As for the BOV open or closed at idle, yes it's "better" or "should" be closed. Besides about the metered air of MAF, if the BOV is not recirculated, that become one of causes how some objects or/and unfiltered air get inside. But at idle, the valve is very soft and probably some people have it slightly open without knowing. Actually it's not a big deal in case if the BOV is recirculated, if it's SD, if the BOV is located pre MAF sensor. That's what Paul and Justin were talking.
Anyways even if the valve is a bit open at idle, the valve should get closed once you open the throttle and it gets open once you off the throttle if the spring is the one for you.
I asked you if you confirmed if open or closed because if it's open at idle, it should have been working after partial throttle but you said it's not working/opening. It actually doesn't make sense to me or I am not understanding well what you meant.

Again, if I understood the case correctly, then I still recommend to go with a softer spring than the recent 11 psi spring. Usually the originally spring, the one comes with a BOV should work for most of case, but in case if it doesn't, why don't you try the one between the original one and the 11 psi? (The one a little stiffer than the original spring and softer than the 11 psi.) I don't know why you skipped that.
I don't think so but in case if there is no spring that matches for what you want or if you want set it exactly how you want, then replace the BOV with an adjustable BOV, like Japanese brands which are usually adjustable and no need to select a spring. Usually just run the engine and adjust it until the valve gets closed at idle. I believe that's the point you are wanting.

 

[curt-s]

What I'm still scratching on is the fast +/- 2psi pressure changes on a flat throttle position as RPM very slowly increases.. That's a not-insignificant amount of air mass in the whole of the intercooler piping to gain and lose that fast. Easy when you have throttle changes, but when you don't, it should be much flatter than that in a slow climb even if he was leaking out of the BOV.

 

[Justin DuBois]

I'm using a Greddy Type-S - which would behave the same as this Tial if I only used the upper port on the diaphragm. I could never get the part throttle smooth release by only using the top port. With nearly no pressure on the spring, the part throttle would be good, but then it would not hold maximum boost. When I set the spring tension to hold boost, then it would surge the compressor at light lifts.

The only way I could get the BOV to perform for me was to also use the port on the bottom, plumbed to a port on the TB that only sees boost. The lower port would push the valve open in combination with the vacuum on the top lifting the valve open - but only when the throttle started to close.

Esentially, the boost top and bottom are equal pressure WOT, and the spring holds the valve closed for maximum boost. Every other time (part throttle, closed throttle) - the differential between before and after the throttle body overcomes the spring mechanically, and opens when it should - to release pressure when you don't need it.

Without boost pressure lifting the valve open from the bottom, it's going to be very fussy. This is a drag car BOV. Not really designed for smooth throttle response.

 

[silentsnow31802]

Video!
1st through 3rd gear. Surge in 2nd and 3rd.

You must be logged in to view this image or video.

 

[curt-s]

Interesting. Can you post a log of that too?
I'm curious what the wastegate is doing..
Since you have this happen at under 10psi in your last log and your acceleration isn't taking off in second, overboosting from a faulty solenoid and misreporting MAP sensor can't be the culprit. You have your gauge connected to the P port but you don't read vacuum -- that's extremely odd. That port is open to the plenum side and you should be getting both boost and vac.
For instance, this is me (the other ports are sealed closed with epoxy)

You must be logged in to view this image or video.

Have you tried plumbing your J-pipe directly to your wastegate? It will open at WG spring pressure which is 11psi if you're using the factory actuator. Maybe a bit less if it's older and tired. Just taking things out of the equation.

 

[silentsnow31802]

Interesting. Can you post a log of that too?
I'm curious what the wastegate is doing..
Since you have this happen at under 10psi in your last log and your acceleration isn't taking off in second, overboosting from a faulty solenoid and misreporting MAP sensor can't be the culprit. You have your gauge connected to the P port but you don't read vacuum -- that's extremely odd. That port is open to the plenum side and you should be getting both boost and vac.
For instance, this is me (the other ports are sealed closed with epoxy)

You must be logged in to view this image or video.

Have you tried plumbing your J-pipe directly to your wastegate? It will open at WG spring pressure which is 11psi if you're using the factory actuator. Maybe a bit less if it's older and tired. Just taking things out of the equation.

I will try tomorrow and get a log along with another video so the two can match up. However the log I already posted is pretty much exactly what that video shows in 3rd gear. Same noses and same feeling.
My specific throttle body has the P port on the pipe side. There is a difference in model years. My car is a 93 but under the hood is kinda Frankenstein.
My boost control solenoid is hooked to the J pipe at the moment. I can bypass the solenoid and hook it directly to the wastegate to test. Thats not a bad idea. Curious what happens.

Just to make note, all of the electronics and the turbo is new. The BOV and wastegate are used. Turbo was rebuilt a few hundred miles ago and the car was converted from old 90s mechanical everything to electronic and DSMlink very recently by me.

 

[curt-s]

Most of our cars are frakensteins in one way or another. My TB is from a Canadian market 91 Talon, the rest of the motor is a JDM GVR4 RS. Our TBs are the same. To my recollection, there are three model years for Turbo TBs: 90, 91-94, and 95-99.

I asked for a log for this video because the one you posted is a 5 second log from a specific event. It's missing second gear, it's missing first gear.. it's missing general movement around. Sometimes the devil is in the details located somewhere else. Being able to correlate log data with visual cues can be helpful as well.

 

[silentsnow31802]

Most of our cars are frakensteins in one way or another. My TB is from a Canadian market 91 Talon, the rest of the motor is a JDM GVR4 RS. Our TBs are the same. To my recollection, there are three model years for Turbo TBs: 90, 91-94, and 95-99.

I asked for a log for this video because the one you posted is a 5 second log from a specific event. It's missing second gear, it's missing first gear.. it's missing general movement around. Sometimes the devil is in the details located somewhere else. Being able to correlate log data with visual cues can be helpful as well.

See this post:

Taboo speed shop vacuum diagram and removal for 1g and 2g.

I've noticed a few threads with people looking for these pictures since the website is no longer available. A wiseman suggested that I post them in a tech article so here they are. I was going to include the original text from the taboo site, but the site does not support the right click...

www.dsmtuners.com

"In 1993, the P-port was moved from the plenum side of the throttle plate to the intercooler side like every other port."

You must be logged in to view this image or video.

I seem to still have my original 93 throttle body.
This is why I was seeing 0 at the boost gauge using the P port while idling.

Tomorrow I will get another video along with a log to match up the two.

 

[curt-s]

Well, there you have it. I completely stand corrected and didn't see that thread in my (short) research. This was definitely a learning experience on the 1Gb.
The 1Ga P port is plenum, the 2G port is plenum, based on the FSM

You must be logged in to view this image or video.

So for two model years in the middle they changed it..?

 

[silentsnow31802]

Well, there you have it. I completely stand corrected and didn't see that thread in my (short) research. This was definitely a learning experience on the 1Gb.
The 1Ga P port is plenum, the 2G port is plenum, based on the FSM

You must be logged in to view this image or video.

So for two model years in the middle they changed it..?

Seems that way. No idea why they would.
Just means I only have 2 ports available that will show vacuum at idle.