VNT controling, anything new? - PeachParts Mercedes-Benz Forum

clacker · #1 05-01-2013, 11:18 AM

So I have searched around and most posts are a couple years old now (and missing key photos), anything new or exciting to read about? I am replacing turbos on two projects, and want to go VNT but need some guidance...before I spend a grand each on replacement turbos (not going the junkyard route, want new stuff). Both projects are 80s diesels pre electronics. If I need to make it semi electronic thats fine, so long as there is guidance and reliability/simplicity (road tripping not daily commuting).
My goals are early boost for drivability NOT ultimate performance, I cannot source a small frame turbo to fit so that is out of the question (new that is, all these old Garrett units are long obsolete), GT28 is the smallest option available in T3 form (bolt on) which is very large!
First project is a Winnebago Lesharo with Renault J8S 234 2.0L turbo diesel, other is a 300SD and 240D (parallel projects).
The Winnebago has a smaller turbo (TAO305) compared with Mercedes tds a/r 0.36 turbine vs 0.42 but otherwise identical.

Simpler=Better · #2 05-01-2013, 11:53 AM

I would reconsider the junkyard route. A $100 GT2056V with blown seals should only be $400 tops to rebuild it.

As for controlling them, electronic vacuum valves for multi stage boost and a boost/vac actuator seems to be the easiest route with plenty of flexibility.

tomnik · #3 05-01-2013, 12:25 PM

not that I want to drag you away from your plan but it seems that building a correctly working VNT controller is a big project.
Did you think about a ball bearing turbo i.e. BorgWarner EFR series?
For my SD I modified a GT25 VNT to fit to the flange but finally failed controlling it.
On my 603a I still run the stock turbo but with bigger element IP. There is no turbo lag any more with powerful low end torque.
I am in progress to upgrade with a ball bearing turbo (BorgWarner off V12 AMG, one bank). No idea how this will run but for sure I don't need a VNT.

What I know about VNT control:

input:
- pedal position for setting the desired boost
- actual boot signal

output:
- pwm signal to control a vacuum valve (proportional valve)

Let me know and I'll search on my computer what I collected about VNT controller.

Tom

Simpler=Better · #4 05-01-2013, 12:53 PM

I had my 2056v setup to either build 8psi or 18psi, and do it quickly. If I was driving relaxed I would leave the switch in 8psi mode, if I was going fast I would put it into 18psi mode. Far from perfect but workable

clacker · #5 05-02-2013, 09:16 AM

I am looking for basic setup info, I build long term reliability into my project (once done don't have to go there again!) and am looking for guidance on the vnt setup. I don't mind tweaking or playing with something to correct smoke or certain performance traits, but I need guidance on the how too part. I am very familiar with how the VNT works (13 years with a TDI daily driver), I want that addictive boost on my other vehicles rather than a minutes worth of turbo lag! I am only going new turbos, VNTs are way to sensitive to vanes sticking etc to bother with used (have experience with them!).

What I don't understand is why pedal or throttle position has ANYTHING to do with the control set up, it should be set to max boost all the time until less boost is needed no? As in full boost then back off the vanes to have no lag. The Winnebago is moving 21' and 7000lbs with 75hp, it needs some help! It is fine once your moving on the highway, it is getting off the line at low speeds that make things interesting, having boost come on around 1500 rpm rather then way over 2000rpm would make a huge difference.
Anyways, discuss away, inform me!

clacker · #6 05-02-2013, 09:20 AM

I also have complete control systems for VNT off VW tdi, meaning vacuum pot on turbo, harness/lines, N75 valve, ecu etc. I would love to make it all work that way, anyone familiar with that stuff?

tomnik · #7 05-02-2013, 03:57 PM

I studied the VNT controller in a VW with AFN engine.
Basically the vanes are open for low back pressure and low EGT.
Once the driver pushes the pedal the controller "knows" the desired boost, depending on throttle position. Each throttle position has its desired boost level.
Again, the driver pushes the pedal, immediately the vanes close to max. closed position, boost rises until desired boost is reached. Fast start up, slow approach to avoid over peak. I think this is called PID behaviour.
If the pedal is released after hard acceleration the vanes open as pedal position is zero.
In reality the desired boost is set higher at idle (pedal position = zero) than the turbo can do at that time. The vanes are rather closed trying to build up boost but can't as not enough rpm. This gives fast response and it does not matter to have closed vanes at idle. Coming from high rpm after hard acceleration the vanes have to decrease boost and open completely until boost is down.

The VW ECU has many more input like air mass flow and all including the engine management is integrated in one unit.

In my opinion the most attractive way to do a stand alone unit is with Arduino (because of the PWM output for the N75).

Tom

winmutt · #8 05-02-2013, 11:00 PM

Quote:

Originally Posted by tomnik

I studied the VNT controller in a VW with AFN engine.
Basically the vanes are open for low back pressure and low EGT.
Once the driver pushes the pedal the controller "knows" the desired boost, depending on throttle position. Each throttle position has its desired boost level.
Again, the driver pushes the pedal, immediately the vanes close to max. closed position, boost rises until desired boost is reached. Fast start up, slow approach to avoid over peak. I think this is called PID behaviour.
If the pedal is released after hard acceleration the vanes open as pedal position is zero.
In reality the desired boost is set higher at idle (pedal position = zero) than the turbo can do at that time. The vanes are rather closed trying to build up boost but can't as not enough rpm. This gives fast response and it does not matter to have closed vanes at idle. Coming from high rpm after hard acceleration the vanes have to decrease boost and open completely until boost is down.

The VW ECU has many more input like air mass flow and all including the engine management is integrated in one unit.

In my opinion the most attractive way to do a stand alone unit is with Arduino (because of the PWM output for the N75).

Tom

The guy who did the VNT with pneumatic vane control and posted about it on the vw board (libbypapa something I think) contacted me on STD a month or so ago. Sounded like he was going to pick up the arduino project. I will send him your way.