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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > "Tuning" a BOV?



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      10-15-2009, 02:24 AM   #1
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Question "Tuning" a BOV?

I recently picked up a TiAl BOV kit. I have been running OEM replacement Forge DVs with the yellow springs for about 25k miles and have been very satisfied with the performance, but I wanted to try something new.

I have no experience with BOVs... always thought it was cool that you could "tune" the Forge DVs with different springs depending on boost so I was stoked that you could do something similar with the TiAl BOVs. You could select a specific spring for your valve according to the engine's vacuum at idle:
http://www.tialmedia.com/documents/w3_tial_bov50_sp.pdf

-22 and -23 in/Hg Pink -12 Psi (-24 in/Hg )
-18 and -21 in/Hg Un-painted -11 Psi (-22 in/Hg )
-14 and -17 in/Hg White -9 Psi (-18 in/Hg )
-10 and -13 in/Hg Black -7 Psi (-14 in/Hg )

So for the N54 which idles at -20 in/Hg, the appropriate spring to use would be the unpainted spring. However, I'm confused about a few things and I haven't been able to find answers that are consistent or definitive.

1. Is the valve *supposed* to be open during idle? What about during cruise (off boost)?

2. If the N54 idles at about -20, and per the recommendations above we use the unpainted spring rated at -22, does the -22 mean that it requires -22 in/Hg of vacuum to overcome the spring and keep the valve open? Doesn't that imply the valve will remain closed during idle? (which really contradicts what I've read elsewhere that the valve is *supposed* to stay open at idle).

3. From what I've been told, most standard TiAl kits for our cars come with the white spring preinstalled, and it seems to work just fine. However, would switching to stiffer spring (unpainted) result in faster response between shifts, hold booster better, etc. (similar to changing the Forge DV springs from green to yellow)?
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      10-15-2009, 07:40 AM   #2
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I recently picked up a TiAl BOV kit. I have been running OEM replacement Forge DVs with the yellow springs for about 25k miles and have been very satisfied with the performance, but I wanted to try something new.

I have no experience with BOVs... always thought it was cool that you could "tune" the Forge DVs with different springs depending on boost so I was stoked that you could do something similar with the TiAl BOVs. You could select a specific spring for your valve according to the engine's vacuum at idle:
http://www.tialmedia.com/documents/w3_tial_bov50_sp.pdf

-22 and -23 in/Hg Pink -12 Psi (-24 in/Hg )
-18 and -21 in/Hg Un-painted -11 Psi (-22 in/Hg )
-14 and -17 in/Hg White -9 Psi (-18 in/Hg )
-10 and -13 in/Hg Black -7 Psi (-14 in/Hg )

So for the N54 which idles at -20 in/Hg, the appropriate spring to use would be the unpainted spring. However, I'm confused about a few things and I haven't been able to find answers that are consistent or definitive.

1. Is the valve *supposed* to be open during idle? What about during cruise (off boost)?

The N54 is not a mass air meter car so you can have the valve open or closed at Idle, however what you need to look at is that under immediate accel(WOT) the valve doesnt momentarily open as the factory diverters do under high boost. you want the lightest spring you can use as long as the valve closes under all forms of acceleration(boost)

2. If the N54 idles at about -20, and per the recommendations above we use the unpainted spring rated at -22, does the -22 mean that it requires -22 in/Hg of vacuum to overcome the spring and keep the valve open? Doesn't that imply the valve will remain closed during idle? (which really contradicts what I've read elsewhere that the valve is *supposed* to stay open at idle).

Yes in theory, but in practice u need to test!

3. From what I've been told, most standard TiAl kits for our cars come with the white spring preinstalled, and it seems to work just fine. However, would switching to stiffer spring (unpainted) result in faster response between shifts, hold booster better, etc. (similar to changing the Forge DV springs from green to yellow)?
Read above again, you need to test this on your car, its easiest to see on a dyno as long as the fyno loads the car as if its in a road going situation!
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      10-15-2009, 08:08 AM   #3
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Quote:
Originally Posted by XPO186 View Post
I recently picked up a TiAl BOV kit. I have been running OEM replacement Forge DVs with the yellow springs for about 25k miles and have been very satisfied with the performance, but I wanted to try something new.

I have no experience with BOVs... always thought it was cool that you could "tune" the Forge DVs with different springs depending on boost so I was stoked that you could do something similar with the TiAl BOVs. You could select a specific spring for your valve according to the engine's vacuum at idle:
http://www.tialmedia.com/documents/w3_tial_bov50_sp.pdf

-22 and -23 in/Hg Pink -12 Psi (-24 in/Hg )
-18 and -21 in/Hg Un-painted -11 Psi (-22 in/Hg )
-14 and -17 in/Hg White -9 Psi (-18 in/Hg )
-10 and -13 in/Hg Black -7 Psi (-14 in/Hg )

So for the N54 which idles at -20 in/Hg, the appropriate spring to use would be the unpainted spring. However, I'm confused about a few things and I haven't been able to find answers that are consistent or definitive.

1. Is the valve *supposed* to be open during idle? What about during cruise (off boost)?

2. If the N54 idles at about -20, and per the recommendations above we use the unpainted spring rated at -22, does the -22 mean that it requires -22 in/Hg of vacuum to overcome the spring and keep the valve open? Doesn't that imply the valve will remain closed during idle? (which really contradicts what I've read elsewhere that the valve is *supposed* to stay open at idle).

3. From what I've been told, most standard TiAl kits for our cars come with the white spring preinstalled, and it seems to work just fine. However, would switching to stiffer spring (unpainted) result in faster response between shifts, hold booster better, etc. (similar to changing the Forge DV springs from green to yellow)?
The white spring is not heavy enough as it will stay open at idle... You don't want the BOV open at idle... The unpainted spring is what you want as this is what I have and it works perfectly
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      10-15-2009, 10:37 AM   #4
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Quote:
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The white spring is not heavy enough as it will stay open at idle... You don't want the BOV open at idle... The unpainted spring is what you want as this is what I have and it works perfectly
interesting...i may have to look for the spring kit so i can try the unpainted one. i think i saw it somewhere for like $25.
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      10-15-2009, 10:49 AM   #5
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Quote:
Originally Posted by TTurboBullett View Post
1. Is the valve *supposed* to be open during idle? What about during cruise (off boost)?

The N54 is not a mass air meter car so you can have the valve open or closed at Idle, however what you need to look at is that under immediate accel(WOT) the valve doesnt momentarily open as the factory diverters do under high boost. you want the lightest spring you can use as long as the valve closes under all forms of acceleration(boost)
Ok, the open OR closed makes sense since we are TMAP and not MAF. It's been a long time since I've even driven a car with stock DVs so I probably don't even know what momentary opening of the stock DVs feels like, but what/why would they do that? I've got a buddy that's been running a TiAl BOV on his car for a while now and he was trying to explain that when shifting casually, there would be an ever so slight hesitation in throttle response (and he assumed it was because the piston would fully open off throttle during the shift, but would take moment too long to fully close again). During fast shifting though, he said it did not feel the hesitation at all. Any idea why the response would be different in these two situations?


Quote:
Originally Posted by TTurboBullett View Post
2. If the N54 idles at about -20, and per the recommendations above we use the unpainted spring rated at -22, does the -22 mean that it requires -22 in/Hg of vacuum to overcome the spring and keep the valve open? Doesn't that imply the valve will remain closed during idle? (which really contradicts what I've read elsewhere that the valve is *supposed* to stay open at idle).

Yes in theory, but in practice u need to test!
I think flem's response above answers this.

Quote:
Originally Posted by TTurboBullett View Post
3. From what I've been told, most standard TiAl kits for our cars come with the white spring preinstalled, and it seems to work just fine. However, would switching to stiffer spring (unpainted) result in faster response between shifts, hold booster better, etc. (similar to changing the Forge DV springs from green to yellow)?
Read above again, you need to test this on your car, its easiest to see on a dyno as long as the fyno loads the car as if its in a road going situation!
This is probably a subjective thing.
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      10-15-2009, 11:11 AM   #6
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Quote:
Originally Posted by flem View Post
The white spring is not heavy enough as it will stay open at idle... You don't want the BOV open at idle... The unpainted spring is what you want as this is what I have and it works perfectly
Thanks... this is the type of input I've been looking for because it reassures me ppl who install BOVs are after some kind of performance benefit and not purely for the sound

I found this thread on a corvette forums:
http://forums.corvetteforum.com/c5-f...ch-spring.html

There's a guy there saying the valve should be open at idle.

However, is the BOV sucking air in at idle? Or pushing air out? If it's pushing air out, why are people still "filtering" their DIY DV to BOV conversions?

Quote:
Originally Posted by import36 View Post
interesting...i may have to look for the spring kit so i can try the unpainted one. i think i saw it somewhere for like $25.
Yeah, that sounds about right... I've seen it for 25-30.
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      10-15-2009, 11:37 AM   #7
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Thanks... this is the type of input I've been looking for because it reassures me ppl who install BOVs are after some kind of performance benefit and not purely for the sound

I found this thread on a corvette forums:
http://forums.corvetteforum.com/c5-f...ch-spring.html

There's a guy there saying the valve should be open at idle.

However, is the BOV sucking air in at idle? Or pushing air out? If it's pushing air out, why are people still "filtering" their DIY DV to BOV conversions?
There is really no reason (to my knowledge) for the BOV to be open at idle on a turbo car... The BOV will suck air in at idle because you are operating under vacuum... The reason the Corvette guys want it open at idle is because they are using superchargers
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      10-15-2009, 11:51 AM   #8
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Quote:
Originally Posted by XPO186 View Post
I recently picked up a TiAl BOV kit. I have been running OEM replacement Forge DVs with the yellow springs for about 25k miles and have been very satisfied with the performance, but I wanted to try something new.
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      10-15-2009, 11:59 AM   #9
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Quote:
Originally Posted by flem View Post
The white spring is not heavy enough as it will stay open at idle... You don't want the BOV open at idle... The unpainted spring is what you want as this is what I have and it works perfectly
Thats very inaccurate, I had the white springs in my tial and it stayed shut at idle. Also i'm just gonna paste what the vendor tturbobullet said because he is right.

The N54 is not a mass air meter car so you can have the valve open or closed at Idle, however what you need to look at is that under immediate accel(WOT) the valve doesnt momentarily open as the factory diverters do under high boost. you want the lightest spring you can use as long as the valve closes under all forms of acceleration(boost)

The spring doesn't shut the BOV high vacuum and boost closes the BOV and holds it shut.
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      10-15-2009, 12:03 PM   #10
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Quote:
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There is really no reason (to my knowledge) for the BOV to be open at idle on a turbo car... The BOV will suck air in at idle because you are operating under vacuum... The reason the Corvette guys want it open at idle is because they are using superchargers
No it doesn't suck in air our turbos are so efficient that it blows out air at idle. Don't believe me do a test or let me find a video.

http://www.kewego.com/video/iLyROoafY7i4.html
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      10-15-2009, 12:28 PM   #11
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Thats very inaccurate, I had the white springs in my tial and it stayed shut at idle. Also i'm just gonna paste what the vendor tturbobullet said because he is right.

The N54 is not a mass air meter car so you can have the valve open or closed at Idle, however what you need to look at is that under immediate accel(WOT) the valve doesnt momentarily open as the factory diverters do under high boost. you want the lightest spring you can use as long as the valve closes under all forms of acceleration(boost)

The spring doesn't shut the BOV high vacuum and boost closes the BOV and holds it shut.
It stayed completely shut at idle? The white spring that was in my TiAL didn't keep the valve completely shut. And according to TiAL the white spring is the spring to use for -14 to -17 in/hg of vacuum. As stated above the N54 idles @ -20 in/hg which means, according to TiAL (and what I have experienced), the unpainted spring is the way to go.

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No it doesn't suck in air our turbos are so efficient that it blows out air at idle. Don't believe me do a test or let me find a video.

http://www.kewego.com/video/iLyROoafY7i4.html
Yeah I watched this video and it seems to defy all logic. I'm not saying the video is incorrect. I might put the white spring back in my TiAL to see if that is the case
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      10-15-2009, 12:36 PM   #12
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I noticed it when I first put it in that my tial stayed shut at idle and would only open to blow off. I asked stett what springs where he putting in them and he told me the white ones. I thought so too when I first installed my ******** BOV that it would be sucking air in, but when I put my hand there it was blowing it out.
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      10-15-2009, 12:47 PM   #13
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The N54 provides positive Boost Air at all times (open or closed) and only ever sees boost pressure from the Charge Pipe which means it's always blowing air out, so there is no need to filter the Bov. The charge pipe never sees vacuum. Having the BOV open at idle or at cruise alleviates any unnecessary stress on the turbo's or engine and improves mpg.

Without any load on the engine without the car moving, even if you rev it, all the intake will see is vacuum.........not boost. Once you're under way and the throttle body begins to open, the BOV shuts very quickly and allows the turbo's to build boost. The Synapse approach is more ideal than a spring loaded BOV in this situation as it allows it to be open when not in boost and closed when boosting. The way it should be.

Last edited by Sparky66; 10-16-2009 at 10:35 AM.
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      10-15-2009, 12:52 PM   #14
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so conclusion is stick with the white ones that are give or change to unpainted? (at around 14 -15psi)
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      10-15-2009, 01:32 PM   #15
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so conclusion is stick with the white ones that are give or change to unpainted? (at around 14 -15psi)
It's your preference... Are you okay with it being open at idle and venting the positive pressure generated by the turbos? Or do you want it closed at idle?
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      10-15-2009, 05:03 PM   #16
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Hey Flem, did you ever get to run your car with the white springs? If so did you notice any difference or improvement in throttle response? Discernible compressor surge?
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      10-15-2009, 08:48 PM   #17
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Quote:
Originally Posted by Terrance28 View Post
Thats very inaccurate, I had the white springs in my tial and it stayed shut at idle. Also i'm just gonna paste what the vendor tturbobullet said because he is right.

The N54 is not a mass air meter car so you can have the valve open or closed at Idle, however what you need to look at is that under immediate accel(WOT) the valve doesnt momentarily open as the factory diverters do under high boost. you want the lightest spring you can use as long as the valve closes under all forms of acceleration(boost)

The spring doesn't shut the BOV high vacuum and boost closes the BOV and holds it shut.
Ok, I've been thinking about this and i need a bit of clarification on this.

Please correct me if I'm making assumptions here.

If you go on immediate accel (WOT), it seems boost in the chargepipe overcomes the spring pressure in the valve, thus opening it (I'm assuming this is the abrupt opening of the stock DVs that was described). At that moment when the throttle plate opens, is the manifold still in vacuum when this occurs (at that very moment the valve opens up)?

And when the valve shuts after that (possible) abrupt opening, is there a large difference across the throttle body between manifold pressure and chargepipe/intercooler pressure? Are they pretty much equal when the manifold is in full boost (per the boost gauge)?
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      10-16-2009, 09:41 AM   #18
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Hey Flem, did you ever get to run your car with the white springs? If so did you notice any difference or improvement in throttle response? Discernible compressor surge?
The white spring is open at idle (double checked last night) but as Terrance has been saying there is positive pressure in the upper pipe so that isn't a huge deal. I like having the peace of mind and put my unpainted spring back in though.

I have only had the tiniest bit of compressor surge with the unpainted spring. Maybe once or twice in the 6 months I have had the tial in the car.

But as far as what spring you should use? It's up to you.

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Ok, I've been thinking about this and i need a bit of clarification on this.

Please correct me if I'm making assumptions here.

If you go on immediate accel (WOT), it seems boost in the chargepipe overcomes the spring pressure in the valve, thus opening it (I'm assuming this is the abrupt opening of the stock DVs that was described). At that moment when the throttle plate opens, is the manifold still in vacuum when this occurs (at that very moment the valve opens up)?

And when the valve shuts after that (possible) abrupt opening, is there a large difference across the throttle body between manifold pressure and chargepipe/intercooler pressure? Are they pretty much equal when the manifold is in full boost (per the boost gauge)?
That won't happen with the tial. The upper pipe and manifold should be seeing close to the same pressure (maybe a 1/10 psi difference).
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      10-16-2009, 10:00 AM   #19
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Everything I've read shows no advantage of using a BOV over DV and vice versa other than BOV's on our cars suck in unfiltered air. Correct me if I am wrong.


I personally do not like the BOV vacuum cleaner sound I associate them with and they suck in unfiltered air into the engine.
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      10-16-2009, 10:06 AM   #20
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Everything I've read shows no advantage of using a BOV over DV and vice versa other than BOV's on our cars suck in unfiltered air. Correct me if I am wrong.
I thought the same... But after Terrance and I discussed it above (I had to read a bit about it as well) the N54 makes positive pressure at idle so it actually blows air out if the BOV is open at idle
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      10-16-2009, 10:27 AM   #21
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I'm not really worried about anything getting sucked in... the chargepipe side never sees vacuum.

What I'm still agonizing about is which spring gives the best *performance benefit*, while trying to prevent instances of compressor surge.

I know that for Forge DVs, the heavier yellow springs are the way to go for tuned cars. But even with these, I've had some occasional flutter. Does anyone happen to know if the yellow springs allow the DVs to divert back to the intake at idle? In other words, do the yellow springs allow the Forge units to be open at idle/cruise?
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      10-16-2009, 10:42 AM   #22
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Everything I've read shows no advantage of using a BOV over DV and vice versa other than BOV's on our cars suck in unfiltered air. Correct me if I am wrong.


I personally do not like the BOV vacuum cleaner sound I associate them with and they suck in unfiltered air into the engine.
I'm sorry but you are wrong............the charge pipe never sees vacuum hence the DV's or BOV will always blow air out, never suck in.
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