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Old 08-01-2013, 08:50 AM   #1
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Default Boost levels and control question... (Vacuum line related)

So... I may be way off here, but I'm curious if I'm not...

First, my setup...

'90 1.6 shitbox
Greddy manifold & Turbo
TurboTony Downpipe
RX8 Injectors
DIYPnP

With this setup, the car would hit 5.5 psi and hold it fairly decently to redline. (Vacuum

I just added a front mount, nothing too huge but decent size... Its an ABD made for a MK4 1.8t.. 2" inlets, 20" or so core, blah blah blah.

After the install, the car would hit 6psi (I tightened the wastegate arm a little more than before the intercooler), then would taper off, fighting to hold 4.5 psi by redline... No big deal, I figured as much.

I had an AVCR laying around in my shed, so I figured I would throw it in and use it to up the boost and help control it better... So I installed it, running the vacuum lines from the compressor outlet to the solenoid, then to the wastegate. I tee'd into the FPR vacuum line for the AVCR boost sensor. Even with the solenoid electrical connector unplugged from the solenoid, it would spike to 14psi (To which I obviously stopped instantly)... I tried all vacuum line configurations, etc etc.

I did a bunch of research, and I read that sometimes with a small turbo, that the inner diameter of vacuum lines, as well as the length of vacuum lines can greatly affect boost. I also decided to change my boost source from the compressor outlet to one of the nipples on the throttle body. This allowed me to hold at about 10psi, and it holds very solidly with the AVCR.

My questions are this... Is there any validity to the inner diameter of vacuum line & length theory? I have different size vacuum lines on the MS, the BOV, and the AVCR... I used the crap I had laying around. I am planning on purchasing a long length of one size vacuum line, and shortening / cleaning up everything, but I'm curious about what I should setup and how.

I apologize if I'm rambling, and making no sense... But coffee hasn't kicked in yet.

Oh yeah one more thing... The vacuum ports on top of the throttle body. Are those pre-post the butterfly? Curious if I need to drill a hole in my charge pipe and use that for a boost source right before the throttle body. They look like they are post butterfly, but I don't know if they flow through the casting or something to the front side...
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Old 08-01-2013, 08:53 AM   #2
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what are you trying to convey?
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Old 08-01-2013, 09:28 AM   #3
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Quote:
Originally Posted by Braineack View Post
what are you trying to convey?
Sorry... I had a feeling I was rambling and making no sense. They should really not allow me on the internet before my coffee...

Could the vacuum line inner diameter & length of hoses have caused my overboosting even when the AVCR was off?
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Old 08-01-2013, 09:30 AM   #4
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no.

sounds like that solenoid is plumbed to be closed when off, then you'll make full boost.
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Old 08-01-2013, 09:49 AM   #5
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I tried the following:

using NC and COM with solenoid connected & disconnected
using NO and COM with solenoid connected & disconnected
I can blow through the solenoid when not connected / energized, and there are no vacuum line leaks as I can pinch the lines at the actuator or the compressor outlet and i can no longer blow through the lines, which tells me the solenoid isn't leaking.
Solenoid does click when 12 volts is applied to it, so the solenoid is working.

If I go back to the single short line from actuator to compressor, boost goes back to the way it was. So its something with the solenoid being plumbed in line.
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Old 08-01-2013, 09:52 AM   #6
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got pics of the solenoid?
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Old 08-01-2013, 10:03 AM   #7
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Sure...



Ignore the solenoid placement. I had it mounted on the driver frame rail, but the vacuum line wasn't long enough to reach the intake manifold to try a different boost source than the compressor outlet. It WILL NOT be kept there..

I also apologize for the mess of an engine bay... Its awful right now because I just got it back together and haven't cleaned it all up yet.
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Old 08-13-2013, 01:24 PM   #8
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Mount it upside down on the hood prop holder (in the picture it's right side up)
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Old 08-13-2013, 01:35 PM   #9
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1) Boost reference should be before throttle body, after intercooler.

2) I've tried to feed solenoids from the FPR line before. It never seems to work right.
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