35 psi boost and resultant running problems

[R.O.R-2.0]

like was mentioned.. 35psi is out of its efficiency..

the BV39 is about identical to the VNT17 i believe..

im lucky that my VNT still boosts, its seen over 40 psi before 

[fatmobile]

Sounds like your vanes are stuck closed.
I could easily hit 35 when my vanes were tied closed all the time.
 I think a BV39 is closer to a VNT 16, ha, somewhere between the VNT 15 and the VNT 17.

[R.O.R-2.0]

Sounds like your vanes are stuck closed.
I could easily hit 35 when my vanes were tied closed all the time.
 I think a BV39 is closer to a VNT 16, ha, somewhere between the VNT 15 and the VNT 17.

when my vanes were seized closed, i would hit 35 psi before the neighbors driveway, and its not even 100 yards.. and that 35 psi would come on by about 2500 revs..

and any way you look at it, no small VNT is happy at 35psi.. i dont think i would run anything under atleast a VNT 20 with 30+ psi..

i know about VNTs and overboosting.. im surprised mine is not grenaded.. idk how many times ive heard it scream like a oversped G60..

[regcheeseman]

The vanes cycle open and shut when you turn the ignition on - it's part of the system diagnostics. It will light a red led if there are any problems - and I get green led every time.

However you said that they should be open to limit boost? Is that correct as they would be operating in reverse by my setup.

Mine are set closed at idle and open when you bury the throttle pedal then close progressively as the boost rises, is this the wrong way round?

It would seem so as it shows 15psi at 2000 rpm

[rallydiesel]

Yes that is the wrong way around. In order to avoid overboosting, the vanes must open at higher rpm.

[fatmobile]

Yes it should open as boost rises.
 I use the term open because the wastegated turbos use that term when the waste gate opens and relieves some of the boost pressure.

 This just shows how sturdy these turbos are,
 running that high of boost and a hose pops off,.. yet it survives.

[regcheeseman]

Ok, I was getting confused, I've looked again and the vanes release pressure from the turbine rather than force pressure into the turbine.

I must have had it straight in my head at some point because I've just gone over the code that drives the VNT controller and it is as follows


0 pedal 0 boost - vanes open

Any pedal input tends to close the vanes proportionally

Any boost increase will tend to open the vanes

I need to go and hook the laptop up to it - run debug and check that the sensors are orientated correctly in relation to the mechanical position of the actuators.

[MJF]

emps?  

Exhaust Manifold Pressure. The first thing to monitor with home made vnt controls IMHO. It shows what is happening with vanes.

[regcheeseman]

The first thing to monitor with home made vnt controls IMHO. It shows what is happening with vanes.

Go on... is this how the TDIs control their vanes? Does it work by measuring two different pressures? I tried to google the term and just got electro magnetic pulse information!

[RabbitJockey]

its not how the vanes are controlled on a tdi.  but by measuring the pressure in the exhaust manifold you can get an idea of how efficiently your turbo is working, a 1:1 ratio is ideal, but u can still make more power with more pressure in the exhaust than in the intake.  at some point u have too much more pressure in the exhaust than in the intake, and you are losing more power than u are gaining, and also putting extra strain on the turbo and engine.  when a turbo is being over spun outside of its efficiency range on the compressor map, the emps get higher and higher in comparison to the boost pressure because it is taking more and more energy to maintain the boost and flow as the compressor becomes less and less efficient.  and on top of that when the compressor is working inefficiently it is also pumping air which its much hotter and less dense.

[MJF]

Just install pressure gauge to exhaust manifold. You clearly see when vanes are moving from emp. EMP usually spikes when spooling, goes down when vanes open and usually goes above boost when rpm rises. Depending of size of turbo.

[R.O.R-2.0]

The vanes cycle open and shut when you turn the ignition on - it's part of the system diagnostics. It will light a red led if there are any problems - and I get green led every time.

However you said that they should be open to limit boost? Is that correct as they would be operating in reverse by my setup.

Mine are set closed at idle and open when you bury the throttle pedal then close progressively as the boost rises, is this the wrong way round?

It would seem so as it shows 15psi at 2000 rpm

you want them open at idle, then close when you floor it, then open progressively till you get to your desired boost pressure..

i can make about 15 psi @ 2k rpms with no vane control at all..

when the vanes are closed, your EMPs sky rocket.. when the vanes close, the exhaust side becomes small, and a bit restrictive, but spools great.. then the vanes open, and the exhaust side becomes BIGGER, and flows quite a bit better, especially in the upper RPM range..

[regcheeseman]

Something weird going on with the servo so I unplugged it and pegged the vanes open.

Diagnostics gave me a red light because of the servo - which is reassuring.

And the best I could manage on the run home was 18psi 

I'll hook up the laptop to the VNT controller and run it in debug mode to find out what is going on.....

[RabbitJockey]

i think ideally u would want the vanes to be closed from idle, then open until peak boost, then open more according to rpm.  honestly tho if i were doing it i'd just control it with a boost can and call it good enough ha

[vanbcguy]

i think ideally u would want the vanes to be closed from idle, then open until peak boost, then open more according to rpm.  honestly tho if i were doing it i'd just control it with a boost can and call it good enough ha

If they're closed at idle you'll start building boost at idle, which you probably don't want.  In terms of efficiency, you want the vanes open as wide as possible all the time, closing them only to give you the amount of boost you're looking for - otherwise you're just poking a potato in your tailpipe the rest of the time.