VNT stop screw

[JST]

Is this stop screw always set to the maximum opening angle of the turbine vanes? Or is there a margin from the factory setting?

I ask this because I suffered boost creep above 3000 rpm at 22 psi boost in 5th gear. (GT1749v)

Could some more exhaust flow be possible with changed setting of stop screw?

 

[TDIsyncro]

The set screw position only affects turbo operation below spool. Once the turbo is running high boost and you have boost creep, you can try adjusting rod length longer to open vanes more relative to N75 duty cycle. It is also possable that your turbo is too small for your set-up if you have added lots of fuel.

 

[dieseleux]

Adjuste set screw between 2 to 4 psi at 2000rpm when engine are hot with full vacuum on actuator (bypass N75).
Is not the best procedure but is simple to do and is the result of my observation on many vnt turbo.



Dieseleux

 

[JST]

The set screw position only affects turbo operation below spool. Once the turbo is running high boost and you have boost creep, you can try adjusting rod length longer to open vanes more relative to N75 duty cycle. It is also possable that your turbo is too small for your set-up if you have added lots of fuel.

Looked again; indeed, the stop screw limits full closed position of the vanes instead of full open position.

I've also seen that the vanes are not maximum opened at rest, when I disconnect the bracket that holds the actuator the lever can move a few mm's before the VNT mechanism locks itself.

So making the rod longer should give me some more opening angle that can decrease the boost creep. Am I right?

What I encounter is very high boost after changing gear. Especially in higher gears. Maybe the fuelling should be less in that situation.
This is a fuel log (mg/stroke) in 4th gear (starting at about 3600 rpm and ends at 4600 rpm)
0:0:0:14.282,77.910
0:0:0:14.906,79.000
0:0:0:15.482,78.660
0:0:0:16.074,77.900
0:0:0:16.682,76.690
0:0:0:17.322,76.360
0:0:0:17.962,75.360
0:0:0:18.602,74.410
0:0:0:19.241,72.640
0:0:0:19.849,70.040
0:0:0:20.457,67.880
0:0:0:21.081,65.580
0:0:0:21.721,61.720
0:0:0:22.361,57.460

So after changing from 3th to 4th, fuel quantity is directly almost at maximum level. Maybe this causes high boost peak.

What do you think?

 

[TDIsyncro]

yes, increasing the arm length will allow the vanes to open a bit more. There is also a leverage ratio that the linkage system uses. For every degree the arm moves, the vanes move a greater angle..like 2 degrees, for example. I don't give an exact ratio, because I do not recall what it is. So if you can get 5 more degress on arm, it will mean a much bigger difference to vane angle. Rotating the bearing cartriage relative to the exhaust housing also plays with the range that the vanes can operate, but that means removing the locator pin and you need to very carefull when messing with that option.

regarding the fueling, your EGT should give you a good idea of that situation - do you climb fast past 1400F? Do you hit over 1600F unless you let off? etc. Even better, you should be running a EMP guage, at least temporarily while getting tune/set-up right. When EMPS get in too high of a range you get boost creep. I think ultra long injection durations that some people use to maximize performance from undersized injectors tends to create much higher EMP and EGT's as well. Just something to consider. The goal is to hit the desired power level with a proper injection duration.

 

[dieseleux]

Is important for healthy of turbo and good operation, adjust the stop screw at right position.
If vane is adjust too close make very high EMP at gear change.




Dieseleux

 

[fenwick458]

Is important for healthy of turbo and good operation, adjust the stop screw at right position.
If vane is adjust too close make very high EMP at gear change.




Dieseleux

mine was doing exactly that for months and cuaing flat spots below 3,000rpm before i got the bottom of it. the rod was to short and all it needed was 1.5 turns longer and the problem was cured!

 

[JST]

yes, increasing the arm length will allow the vanes to open a bit more. There is also a leverage ratio that the linkage system uses. For every degree the arm moves, the vanes move a greater angle..like 2 degrees, for example. I don't give an exact ratio, because I do not recall what it is. So if you can get 5 more degress on arm, it will mean a much bigger difference to vane angle. Rotating the bearing cartriage relative to the exhaust housing also plays with the range that the vanes can operate, but that means removing the locator pin and you need to very carefull when messing with that option.

regarding the fueling, your EGT should give you a good idea of that situation - do you climb fast past 1400F? Do you hit over 1600F unless you let off? etc. Even better, you should be running a EMP guage, at least temporarily while getting tune/set-up right. When EMPS get in too high of a range you get boost creep. I think ultra long injection durations that some people use to maximize performance from undersized injectors tends to create much higher EMP and EGT's as well. Just something to consider. The goal is to hit the desired power level with a proper injection duration.

Don't have EGT/EMP gauges installed but I will do this soon.

Injector size can be an issue since I'm running the OEM ones as there isn't a bigger aftermarket option as far as I know. (Commonrail)

 

[dieseleux]

Rod adjustement is only to match n75 ecu map, reality versus virtualty.
Actuator position is mathematical fonction of vacuum versus actuator spring and vacuum is fonction of N75 duty cycle of full vacuum versus atmosphere and duty cycle is result of computation of many sensor and map.
ECU react in two mode, dynamic and static, because feedback loop is too slow to react at full WOT or gear change, N75 map in ecu is there to patch slow static loop and react instantly to put vane in good position, this is why lentgh of rod is important for boost spike.
Stop screw is another story, is there only limit EMP when vane are close and vane close at idle and at gear change, if stop screw are too short, actuator make more time to set at good position and in same time turbo spool more fast (not good in high EMP), the result is boost spike.



Dieseleux

 

[im570rm]

just adjust the actuator till you get 70-80% duty cycle on channel 11 @ 4000 rpm.

 

[TDIsyncro]

Don't have EGT/EMP gauges installed but I will do this soon.

Injector size can be an issue since I'm running the OEM ones as there isn't a bigger aftermarket option as far as I know. (Commonrail)

ok. This is very intersting now. Common Rail. Which engine code are we talking about? The CR engine here has a actuator position sensor..so rod length change should work really good with that at top end, but it may sacrifice spool up a bit unless you close down the requested position a bit more from idle to spool to compensate.

If your running on the edge of your turbo for common rail and a long injection duration..you must have a DPF delete? What's your anticipated HP on your set-up?

 

[JST]

ok. This is very intersting now. Common Rail. Which engine code are we talking about? The CR engine here has a actuator position sensor..so rod length change should work really good with that at top end, but it may sacrifice spool up a bit unless you close down the requested position a bit more from idle to spool to compensate.

If your running on the edge of your turbo for common rail and a long injection duration..you must have a DPF delete? What's your anticipated HP on your set-up?

It isn't a TDI actually but a 1.9 JTD 8v engine with EDC15C7 control.
So no actuator postion sensor and no DPF.

I have around 160 HP now at 3700 rpm, running at 1.4 bar boost (20,5 psi). Originally I've had a map with 22 psi but then there were 2 problems:
too long boost outside MAP range resulting in limp mode and boost creep in 5th gear. So the tuner lowered the boost request and also lowered the fuel quantity at boost levels above the request, so when it peaks it easier falls back to the requested boost.
So I want to know if this can't be fixed at a normal way, so I can run 22 psi with maximum fueling.

So maybe I do have to tune the stop position to get rid of that high boost peaks at gear changes.