What's the best BOV for our car

[Redline]

Well yeah, on most city streets it's way over the top. But on the freeway the turbo spins a bit during cruise even while still in vacuum. And every day I drive one surface street with 45/50 speed limits all along it and can't resist the occasional boosted pull from the lights, even moreso now that it comes on so smooooth.

This is true. Reason being turbos start making boost before the 0psi point. Even in vacuum, they're adding to the pressure of the system when you start getting into the pedal. I have a boost gauge I can watch very carefully as I listen to the sound of my turbo. It's clear that it's adding airflow to the system before the 0psi point. The BNR does so much less than my K04 ever did, though.

 

[tarnumf]

. It's clear that it's adding airflow to the system before the 0psi point.

Really? Can you see that in logs?
Because my say that's just a split second when WGD > 0 and boost flips from negative to positive.
Less vacuum is associated with more open throttle, I think.

 

[Redline]

Really? Can you see that in logs?
Because my say that's just a split second when WGD > 0 and boost flips from negative to positive.
Less vacuum is associated with more open throttle, I think.

I can see it in logs and I can see in on my boost gauge. When I'm mildly accelerating only the highway and it shows 0 in/mg / 0psi I know the turbo is adding airflow. By contrast, if I'm just cruising stable at 60 or 70, I'm pulling much more in/mg and showing much lower psi, like -6 or so. Basically, the car acts like it's N/A until I start getting into the throttle, and it doesn't take too much for the turbo to start adding airflow to the system.

 

[tarnumf]

So, again, how exactly do you know that "turbo is adding airflow"?

 

[John]

I personally can hear the turbo whine by the time I'm about -3 psi boost. I wouldn't put it as adding airflow but just say I know it's spinning. I can also say the turbo spins a psi or two more negative in the boost compared to using the stock bpv, which I think is because it stays open more reducing drag on the compressor. This characteristic was discussed plenty in a couple old MSF threads.

Tapnstalk

 

[Redline]

So, again, how exactly do you know that "turbo is adding airflow"?

The turbo whine itself, like @John is mentioning, and the measured increase in airflow as shown by my AP and boost gauge. It's not like the turbo STARTS adding airflow @ 0psi and builds from there. It's adding while you're still in the negative manifold pressure range (i.e., vacuum) too.

 

[tarnumf]

The turbo whine itself, like @John is mentioning, and the measured increase in airflow as shown by my AP and boost gauge. It's not like the turbo STARTS adding airflow @ 0psi and builds from there. It's adding while you're still in the negative manifold pressure range (i.e., vacuum) too.

Ok, correct me where I'm wrong, please.
Assuming that we define "turbo is adding airflow" not by ear, but by when wastegate duty is >0.
Intake manifold running on vacuum and turbo building the boost simultaneously - this is the scenario when BPV opens and air will just recirculate. Correct?
So, when WG and turbo are engaged, my logs show that wastegate duty >0 is always when intake pressure is positive.
Right before WGD goes >0, logs can show any level of vacuum, literally -5 psi or -0.5 psi and go into positive in next line - that is about 0.22 second on AP v3.

 

[Mikey]

Never had a problem with the performance and how it worked. That was awesome. Putting that bitch together and having it break in the same spot twice was my only issue. Very nice looking and sounded great.

 

[Redline]

Ok, correct me where I'm wrong, please.
Assuming that we define "turbo is adding airflow" not by ear, but by when wastegate duty is >0.
Intake manifold running on vacuum and turbo building the boost simultaneously - this is the scenario when BPV opens and air will just recirculate. Correct?
So, when WG and turbo are engaged, my logs show that wastegate duty >0 is always when intake pressure is positive.
Right before WGD goes >0, logs can show any level of vacuum, literally -5 psi or -0.5 psi and go into positive in next line - that is about 0.22 second on AP v3.

I'm not sure with reference to WGDC. But I am sure that it's still adding air to the system under part- and moderate-throttle (especially) conditions. Pure N/A cars always stay in vacuum, as I understand it. They don't hit 0, unless for maybe a split second when the throttle plate closes suddenly under hard acceleration.

I wish I could give you more regarding the theory, but I have very little experience with manifold pressure on N/A cars. I can tell you this: turbos can be making pressure with 0 WGDC. Creep is an extreme example of this, but an example nonetheless. Maybe a Motorhead like @Enki can illuminate this more.

 

[Enki]

Turbo can be adding airflow independent of WGDC, correct. Spring pressure is a thing, after all.
You can't directly correlate WGDC with boost pressure on any car because it changes with the VE (which is affected by timing, AFR, elevation, RPM, etc) of an engine.

 

[Redline]

Turbo can be adding airflow independent of WGDC, correct. Spring pressure is a thing, after all.
You can't directly correlate WGDC with boost pressure on any car because it changes with the VE (which is affected by timing, AFR, elevation, RPM, etc) of an engine.

Thanks, man. Yeah, this makes perfect sense @tarnumf. For instance, my spring pressure is ~14psi on my BNR S3. So my car is able to make up to that boost level with 0 WGDC. It is at the point that I try to go beyond 14psi that my ECU/EBCS starts adding in WGDC to go beyond my spring pressure.

 

[tarnumf]

I think you lost me completely..
Seriously, with WDGC = 0, what is the magic holy power charging compressor and "adding airflow"?

 

[Redline]

I think you lost me completely..
Seriously, with WDGC = 0, what is the magic holy power charging compressor and "adding airflow"?

Spring pressure. The turbo will build to it's spring pressure with 0 WGDC. Once it hits spring pressure, it needs to add in WGDC through the EBCS to build boost levels above spring pressure. Easy peasy.
[doublepost=1463542005][/doublepost]Spring pressure. The turbo will build to it's spring pressure with 0 WGDC. Once it hits spring pressure, it needs to add in WGDC through the EBCS to build boost levels above spring pressure. Like I said, on my BNR S3, 0 WGDC will build me up to 14psi, because that's my spring pressure. When I want boost over 14psi, then the EBCS commands the WG to stay closed even longer (normally it opens at spring pressure) so that I can build boost levels over 14psi for my BNR S3. In other words, you'll build boost up to your spring pressure level even with 0 WGDC. Easy peasy.

 

[Enki]

Turbos (on gasoline engines anyways) are operating in an open feedback loop, kind of like when you put a microphone next to a speaker that it's feeding. The wastegate bleeds excess energy from the exhaust that would otherwise cause the turbo to spin up to a fucktillion RPM and explode with violent fervor.

You have some reading to do.

 

[tarnumf]

Turbos (on gasoline engines anyways) are operating in an open feedback loop, kind of like when you put a microphone next to a speaker that it's feeding. The wastegate bleeds excess energy from the exhaust that would otherwise cause the turbo to spin up to a fucktillion RPM and explode with violent fervor.

You have some reading to do.

So, at zero WGDC (or completely open wastegate) all exhaust gases are passed through wastegate without giving any energy to the turbo to add the airflow. Correct?

 

[Enki]

Wrong. The wastegate stays closed until exhaust manifold pressure exceeds wastegate spring pressure.

Truth is, wastegates don't even control boost; they control the amount of energy that *can* go in to the turbo on the hotside. Super efficient head and manifold designs can exceed spring pressure. Shitty or long cold runner setups (I'm looking at you, Subarus) might not get full spring pressure until everything is nice and hot.

Search YouTube for how wastegates work.

 

[Redline]

So, at zero WGDC (or completely open wastegate) all exhaust gases are passed through wastegate without giving any energy to the turbo to add the airflow. Correct?

Zero WGDC is the WG flapper completely closed, not completely open.

 

[tarnumf]

Wrong. The wastegate stays closed until exhaust manifold pressure exceeds wastegate spring pressure.

Zero WGDC is the WG flapper completely closed, not completely open.

Yep, now I figured that out! Thanks for keeping up with me!
Btw that's the article that I found useful: http://blog.perrinperformance.com/boost-control-systems-explained/