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skipdup's Avatar
 
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Wastegate lines

What is the function of the upper and lower lines that attach to the wastegate?

I just realized I either don't know or have forgotten!

Thanks,
Skip
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Old 12-27-2007, 01:37 PM
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The lower one opens the wastegate. The upper one is the vent and should be open to atmosphere unless you are going to use it to allow for some adjustable boost.
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Old 12-27-2007, 02:06 PM
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Quote:
Originally Posted by NathanUK View Post
The lower one opens the wastegate. The upper one is the vent and should be open to atmosphere unless you are going to use it to allow for some adjustable boost.

Hi Nathan,
As I got all the parts now for my stock adjustable wg, I'm wondering how to manage the fact that the "open to atmosphere" will but replaced by the back pressure for adjustment....?.....can you post a schematic...?.... (if differentfrom the TIAL)....thanks

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Old 04-23-2008, 03:41 AM
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Old 04-23-2008, 04:48 AM
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1
Good response
keeps shut while shift gears
small turbo can produce spikes, when the pressure builds in the intake


2
Bad response
doesn't keep shut (creep)
stable counter-pressure

3
very good response
keeps shut while shifting gears
Double acting if check valve is removed, great for drifting when going from 3rd gear to 2ND gear while in higher revs, keep boost from delays
Builds very aggressive boost in the intake

4
Simple construction
stable but slow
doesn't keep shut
loses boost while gear shift
the simplest bleed method
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Old 04-23-2008, 04:49 AM
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Thanks a lot Goran....

So, am I correct, connecting as follow...is that the best way...?

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Old 04-23-2008, 05:48 AM
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Well it depends on what kind of boost knob that is. If it's a pressure regulator then it's possuble to mount it in couple of ways.

There are many schools in how this should be done. OEM 930 approach is to keep the vent open and let the spring tension do the regulation.

Later models with electronic boost control got internal wastegates w/o vent and were regulated by magnetic valve similar to scenario nr.4.

I personally don't have expirience with that particular knob so I won't venture further and give you advice. I'm just trying to explain general ideas in boost-pressure regulation so you could choose according to your needs.


Generally: if separate wastegate is available, the best way to control boost over base boost (base boost = boost determined by spring tension and top side vent open) is by varying pressure on the top side of the bell (vent pipe). This keeps the valve shut untill it opens (no valve creep). There are multiple ways to control this pressure and IMHO the best way is to use EBC with magnetic valve and positive feedback.

Knob-stuff is very cool with it's braided lines but frankly, it's a bit middle-age.

In case your knob just controls the amount of boost vented trough it to athmosphere, then you can connect it the way you drawed. I would connect boost gauge to it's own pipe though as amount of bleed in knob would influence the readings on gauge.
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Old 04-23-2008, 06:42 AM
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The only question I got is... (and I know the factory used this setup plenty) does boost response/ control get hindered becuase of the length of the wastegate lines in this situation(935 gat controler)?
Im going through some crap right as we speak with my car boost creeping and am wondering.
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Old 04-24-2008, 05:37 AM
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Kris, the distance between the IC and the WG is only 60 cm (2 feet...) and all the lines are aviation quality ( 1/10" TEFLON diameter, Stainless steel screen)....but yes, distance from IC to boost knob is 9 feet...x 2 (for return)....I saw a lot of 935 with that knob on the dash board.....
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Old 04-24-2008, 07:36 AM
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Serge,
my car was purchased with an Andial "dial a death" knob similar in operation to the one pictured. Your schematic is correct. The knob regulates pressure through the vent to increase the opening resistance of the wastegate. Positioning of the knob itself should not matter. Mine was tucked up under the dash, but I have seen many in between the seats. Additionally, when installed, mine used rubber fuel line and worked great, so your braided teflon line will be that much better. So long as you can restrain yourself from cranking up the boost when challenged you should be allright.

JP
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Old 04-24-2008, 08:46 AM
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Ok JP....thanks for the information.....
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Old 04-24-2008, 09:03 AM
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