BOV Setup for your N54

[Jeffman]

Update: I removed the white 8 psi spring and installed the plain 10 psi spring. I’m pretty sure my boost is back!

First of all the BOV is now closed at idle with the 10psi spring:

Log with the 8 psi spring showed max 17.8 psi in 3rd gear, 20.7psi in 4th gear:

datazap.me | Jeffman | E34 BPM4 80F 3rd-4th shift

datazap.me

Now with the 10psi spring I’m achieving 22-23 psi max in 3rd and 4th gears as before:

datazap.me | Jeffman | E34 88F Uphill 10psi BOV Spring

datazap.me

So the plain 10psi spring keeps my BOV closed while idling and EDIT[somehow enables higher maximum boost pressures.] NOT SURE WHY???

 

[Chris@VargasTurboTech]

I am sure you are aware of this, but possibly not. The spring has nothing to do with holding the BOV closed under boost. This is why you run a boost reference to the top of the BOV, they often design the top of the piston to have more surface area than the bottom. It is this boost on the top of this piston that holds it closed under boost (more area on top than bottom piston cannot open under boost). You can 100% remove the spring and boost will hold your BOV closed under boost with no leaks, this is how BOV's are designed. If you had a boost leak at the BOV, then after you disassembled and reassembled it the problem was fixed. Most likely whatever was causing the issue, misaligned O-ring, etc, etc was rectified during the reassembly. Changing the spring would have no effect at all on holding it closed under boost, it simply changes the amount of vacuum required to open it. Nothing else.

Chris

 

[Jeffman]

I am sure you are aware of this, but possibly not. The spring has nothing to do with holding the BOV closed under boost. This is why you run a boost reference to the top of the BOV, they design the top of the piston to have more surface area than the bottom. It is this boost on the top of this piston that holds it closed under boost (more area on top than bottom piston cannot open under boost). You can 100% remove the spring and boost will hold your BOV closed under boost with no leaks, this is how BOV's are designed. ... Changing the spring would have no effect at all on holding it closed under boost, it simply changes the amount of vacuum required to open it. Nothing else.

Chris

Yep, that’s what I thought, too. It makes perfect sense that the pressure in the manifold balances the pressure in the chargepipe across the BOV at steady state equilibrium.
But then I started to think about the transient, non-equilibrium scenario during WOT spool-up. Could there actually be a pressure differential across the BOV during spool-up leading to some leakage, as I discussed above? If so, I believe a stronger spring would help to alleviate such leakage.

Maybe this isn’t a problem for a slower-spooling large single turbo, but maybe it can occur for fast-spooling stock twins?

Can’t say for sure without experimental data - maybe I’ll mount a GoPro under my hood to keep an eye on the BOV lol.

 

[Chris@VargasTurboTech]

Well throttle closures can give you a pressure differential, but the right way to fix that isn't a stiffer spring, it's a sane tune. Also, this is the 100% perfect storm for on throttle compressor surge to destroy your turbos in short order. The turbos are building boost, the throttle is closing due to something being wrong in the tune, etc, etc, etc insert reason for throttle closure here. What you WANT at that point is the BOV to relief the pressure differential, and keep your turbos out of surge. What you do NOT want is to jam a spring in there large enough to keep the BOV closed and induce on throttle surge during the throttle closure.

 

[Abacus38]

Or you can be Thug life like the Aussies and run no BOV lol

 

[Jeffman]

No throttle closures!
And the BOV works fine.
(I thank my lucky stars every day for high boost and no throttle closures.)

Hide legend Reset zoom

 

[Chris@VargasTurboTech]

No throttle closures!
And the BOV works fine.
(I thank my lucky stars every day for high boost and no throttle closures.)

Hide legend Reset zoom

Working fine, and not providing a full vent, or on-throttle surge safety net are not one and the same. Yes, they will work with as tight as spring as you want to run in them, or no spring for that matter. Then there is the ideal set-up. There is a reason we run black springs in Tial's and Orange in Raceports.

 

[doublespaces]

I still don't understand why people want a strong spring. It just isn't needed. On decel you'll get -10 psi vacuum. Meaning it can barely open the bov. You want that fucker flying open at the first scent of the engine entering vacuum. People WILL experience more surge and stress on the shaft/bearings.

 

[Payam@BMS]

I still don't understand why people want a strong spring. It just isn't needed. On decel you'll get -10 psi vacuum. Meaning it can barely open the bov. You want that fucker flying open at the first scent of the engine entering vacuum. People WILL experience more surge and stress on the shaft/bearings.

Agreed! I was so annoyed of the flutter from my BOV not venting. I opened the BOV, cut 1-2 coils off the spring and shoved it back in.
No more flutter or boost issues, and I've pushed over 40 psi

 

[fmorelli]

I had scenarios where I would have surge or delay off throttle. Scared the bejesus out of me at speed. At @Chris@VargasTurboTech recommendation, I went to the 6psi black spring. Problems disappeared. I did also go to a proper 1/4" port to the Tial. Nonetheless that combo made my issues disappear.

Filippo

 

[doublespaces]

Let's say you're doing a max on the bench press and you barely hoist it up. That is a 10 psi spring being lifted by 10 psi of vacuum. Then you got the turbo still spinning creating excess pressure that helps pop it open momentarily four or five times creating flutter because the vacuum isnt strong enough to catch the plungers momentum from spring bounce back since the force that helped it open is now gone. Now you might get squeaking noises, potential surge and turbine stress.

If you modulate the throttle when you drive, aka you use the car for anything besides WOT pulls, then you are frequently in this situation where pressure needs to find its way out in a scenario not depicted by tial's end all, be all charts.

There will always be a short instant where the turbo is spooling momentarily against a closed or closing throttle blade until all the air from the manifold is consumed and the vacuum state hits the bov. The stronger the spring the more frequently this will occur. If the bov open at idle bothers people, the answer is a bov filter not a stiffer spring.

 

[Jeffman]

Maybe it’s time for a poll?

TialQ BOV Users: What spring do you use?

TialQ BOV Users: What spring do you use?

bmw.spoolstreet.com

 

[Chris@VargasTurboTech]

No, no poll. No offense but it's not a community discussion, it's a fact. Stop putting giant springs in your BOV's you heathens! (I say that with, uh.... love).

There are a few scenarios you'd consider something different, but by and large, put the black spring on your Tial, the orange one on the Turbosmart, I can't speak for other ones.... run a dedicated line and never worry about it again.

 

[BOosted 335i]

every car is a little different.you should measure your vac and then get the correct spring.

 

[Chris@VargasTurboTech]

Nope, you really want about the lightest spring as you can get to work reasonably with your setup. It'll help with getting a full vent, responsiveness, and keeping surge away. Tial it's gonna be black. If you live on the moon and have your spark plugs gapped to 4", you can look at other springs.

You know what? I'm changing directions. I think you should put all of the springs in there, that way you know that the right one has been covered.

 

[Jeffman]

Let's say you're doing a max on the bench press and you barely hoist it up. That is a 10 psi spring being lifted by 10 psi of vacuum. Then you got the turbo still spinning creating excess pressure that helps pop it open momentarily four or five times creating flutter because the vacuum isnt strong enough to catch the plungers momentum from spring bounce back since the force that helped it open is now gone. Now you might get squeaking noises, potential surge and turbine stress.

If you modulate the throttle when you drive, aka you use the car for anything besides WOT pulls, then you are frequently in this situation where pressure needs to find its way out in a scenario not depicted by tial's end all, be all charts.

There will always be a short instant where the turbo is spooling momentarily against a closed or closing throttle blade until all the air from the manifold is consumed and the vacuum state hits the bov. The stronger the spring the more frequently this will occur. If the bov open at idle bothers people, the answer is a bov filter not a stiffer spring.

I totally understand your points and pretty much agree with you. I will say that the car feels even more responsive driving around today with the plain 10psi spring installed - Perhaps I’m noticing even less of a lag delay now that the BOV is closed more than before with the 8psi? I’m also noticing less BOV whoosh noise when going off throttle which is consistent with Tyler’s discussion. I’ll drive around with the 10psi spring for a little while and see how it goes.

So how did I pick up +4psi at max boost from 18psi to 22psi in 3rd WOT as shown in my logs? @Chris@VargasTurboTech suggests install error, possibly the rubber bladder was pinched. But when I opened up the Tial-Q it looked perfect.

And to be sure, I could change back to the white 8psi spring to double check of my max boost goes back down, but as some of you know changing the springs are a PITA. Here’s my Rube Goldberg method of using a strap wrench plus large zipties to hold the two pieces together while a screw down the six 4mm nuts.

 

[Payam@BMS]

LOL at the zip ties! Thank God for our drill press, that helps me on wastegates and BOV spring changes when alone

 

[Chris@VargasTurboTech]

Also keep in mind that, like me, BOV's sometimes need love. Maintenance. Encouraging words. A smack to make them work properly.

As stated before, my guess? Something funky, incidental. However, that's not really important. Look at these pics. I know the guy that wrote that (I should update it...it's on my list of things to charge Tony extra for).

Let's say your car is perfect. Not even paint swirls. Yet, somehow, under WOT, you're losing out on boost. No boost leaks. It's that infernal BOV and Chris's spring recommendation!

This means that, as shown in figure 1, boost in your charge pipe is, at some point, applying more force than what's in the manifold (plus whatever extra area force multiplication goes on... ignore for now) AND the spring force.

Insert record screeching sound.

What in tarnation could cause such an injustice to the gods of going forward?

Great question. Something that causes a large pressure drop between your charge pipe and your intake manifold, that's what. Like, for example, a partly closed throttle. Either way, if you have ~25 psi in your charge pipe, you damn well better have very close to 25 psi in your manifold, which means.... the valve.... should.... be..... CLOSED. Now if the throttle is being pesky, ok sure. Work on your tune or stop driving your car using the gas pedal like it's PWM (100%... 0%....100%.... 0%).

What else? What about that line. Say that, despite the perfection previously mentioned (still no paint swirls), we have you use a lousy line, or you thought you could get away with using the factory vacuum tap and none of us would notice (HA! WE NOTICED!). Well, I'll make a face while saying it, but now you're impacting your responsiveness and maybe being outright silly. Use a crappy line that swells/crushes and I'm not even going to bother to tell you how it'll work, I'll just tell you to replace it and stop fooling around.

There really isn't a lot more to add to the scenario, although tune is def one of them. Closures, target vs actual, temps, etc.

Chris

 

[doublespaces]

Guys. If you are arguing this, you simply don't have a full grasp of how the blow off valve works. Unlike the wastegate where boost is opening the bypass and the spring corresponds to the boost you are making, with a bov the boost has absolutely no meaningful correlation to the sizing of the spring whatsoever given the context for why people think they need a stiffer one.

 

[fmorelli]

Maybe it’s time for a poll?

Tell you what ... I'll put the stock spring back into my Tial, and have you take it for an hour spirited drive. I just ask that you clean the urine of the driver seat after you wet your pants from the flutter surging at high speed/throttle. lol ... I promise it sucks!

Ok let's get serious. @Jeffman I agree with your line of questioning. Let's assume Chris is right on this one (I believe is). What's causing what you are seeing?

I have one odd question - where did your Tial come from? And where were the spring(s) purchased?

Filippo