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Author Topic: Controlling an external Tial wastegate with the N75  (Read 29599 times)
kenmac
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« on: September 06, 2012, 03:12:07 PM »

I've recently completed a rebuild of a 1.8T with a number of upgraded goodies including a built bottom end and a new turbo kit (PPT).  I'm beginning to move on from fueling on this Stage 3 tune and I'm run into a bit of a snag while tuning and setting up boost control.  I'm unsure at this point if my problem has to do with tuning or hardware but let me explain.

I've used the following boost line configuration for the Tial wastegate which seems to be pretty standard:


My issue is that I do not have any boost control whatsoever.  The boost skyrockets past 30PSI immediately regardless of what I've tried, other than just running directly off of wastegate pressure which is about 14.5 PSI.  In any other configuration, there seems to be zero control.

-I've tried setting KFLDRL to 0 across the board (as a control test). I expected this would effectively be the same as running off of wastegate pressure.  No effect.  However, since the positive pressure is constant (or should be) at the bottom of the wastegate valve, shouldn't I be inverting KFLDRL to run a high duty cycle (bleeding off 95% of boost)?

-So I tried setting KFLDRL to 95.0 across the board.  Again, no effect.  Surely one of these two configurations should have *some* effect on boost control.  But no.  Zero, zilch.

-Then I tried placing a MBC in place of the N75, turned all the way down.  This should allow no flow to the top of the wastegate valve.  Again, no effect.

I assume it's safe to say that my problem is hardware related somehow?  But how?  The wastegate operates normally at 14PSI until it's connected to something on the top of the valve.

I have logs, but they're generally useless.  They just show what I've said above.  Any ideas?
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nyet
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« Reply #1 on: September 06, 2012, 05:07:48 PM »

I'm pretty sure you need to either keep the bottom port at ambient, or somehow limit the amount of boost the lower port sees (compared to the top port), or the WG will never open.

If you keep it at ambient, you may not spool as fast or hold as much boost pressure.
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« Reply #2 on: September 06, 2012, 05:11:26 PM »

Hooked up wrong, only use one port, third n75 line also goes to ambient for the bleed.
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« Reply #3 on: September 06, 2012, 05:14:52 PM »

I just use bottom port.  Top is open.
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kenmac
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« Reply #4 on: September 06, 2012, 05:29:30 PM »

Thanks for the tips guys. I just did a once over of all the lines again and found that the clamp on the bottom port of the wastegate was loose and was leaking.   Roll Eyes

I was wondering if people just run the N75 on the bottom port and this answers my question. It doesn't seem like I have much control using the top port.
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marcellus
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« Reply #5 on: September 06, 2012, 06:23:05 PM »

I always did it like this:

http://forums.audiworld.com/showthread.php?t=1476692
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jibberjive
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« Reply #6 on: September 07, 2012, 11:44:12 PM »

I just use bottom port.  Top is open.
This.
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Gizmo20VT
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« Reply #7 on: November 16, 2012, 03:59:31 AM »

thread bump, did the first post diagram work after securing the clamp?
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« Reply #8 on: November 16, 2012, 10:33:00 AM »

the top diagram is how you do it with some controllers, not the n75

with the n75 when it cycles it would effectively lock the top port and never allow the diaphragm to work
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Gizmo20VT
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« Reply #9 on: November 16, 2012, 06:29:43 PM »

My understanding of it with the above diagram the N75 is connected to the top port, bottom port has a positive pressure source as well hence the T piece in the line. The n75 still receives boost pressure and sends thru to the top port of the WG, once boost levels are acheived the N75 will bleed of pressure into atmos/intake out the 3rd nipple (longest one) making bottom port pressure > top port pressure and then opening wastegate Huh

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prj
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« Reply #10 on: November 17, 2012, 02:54:38 AM »

Just use bottom port only and job done.
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Gizmo20VT
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« Reply #11 on: November 18, 2012, 05:11:33 AM »

If I use bottom port only my car overshoots target by about 200mbar once full boost is achieved.
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matchew
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« Reply #12 on: November 18, 2012, 07:52:12 AM »

Then retune boost control....
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Gizmo20VT
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« Reply #13 on: November 18, 2012, 08:13:09 AM »

Will be doing so matchew, going over s4wiki again, will change the Boost PID I  Smiley

Just wanted to know if there was another successful way of using the N75 on the top port of WG.

Cheers
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marcellus
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« Reply #14 on: November 19, 2012, 02:21:22 PM »

Mine runs on the top port and works just fine. 
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