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morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

So..the spring will be here shortly...the 924 will be up for driving soon.

I'm going to prepare all the items necesary to install the Forge motorsport boost controller that i have. It works by feeding pressure into the top of the wastegate.

Does anyone have pictures of the top(vent) port...i need to know what lines to buy and how will i fix the line onto the wastegate.

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alexvex · Posted: Thu Feb 12, 2009 1:15 am Post subject:

I'm not sure if 931 wastegates have a top port. The pic shows a dual port wastegate, hence the top and side ports....dual ports are generally used with electronic boost controllers.
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--Alex--
1992 Porsche 968 (VW 2.5L I5 Turbo swap in the works)
1995 Audi 90 Quattro Sport (4.2L V8 Swap)
2010 Touareg TDI
Past Pcars: 80 931, 87 924S, 87 951

bass gt · Posted: Thu Feb 12, 2009 1:46 am Post subject:

Morghen,

Yes, the 931 is a dual port design, same unit as fitted to the old 911 turbo's. From memory, the top port is something like an M13x 1.25 fine pitch thread. However, don't take my word for it. You should remove the WG when you do this, so just double check.
also, i would recommend fitting a really low boost value WG spring, such as from a US car. Manual boost controllers can be very finicky, so it's better too start with less and build up. Unless you love replacing head gaskets!! Trust me, i've been there with this one

Steve
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morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

M13...thanks...i figured it would be big.

unfortunately I dont have a weaker spring.

i do have a VDO boost gauge mounted instead of the clock to monitor the boost.

Steve, would you say that feeding the top of the WG with signal could increase the manifold pressure by that much that i can blow it off? i mean the spring is the stock S2 one.
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bass gt · Posted: Thu Feb 12, 2009 5:32 am Post subject:

Morghen,

The trouble with manual boost controllers is they are very difficult to finely tune the boost with. You would be amazed at how much difference a quarter turn makes.
It is then very easy to overboost and pop the head. ask me how i know

Steve
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morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

so a safer way would be just to install a 0.8bar spring or 1bar spring ?
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flosho · Posted: Thu Feb 12, 2009 6:02 am Post subject:

Morgan, a t-style boost controller can be a very effective way to control boost, I've had one on my car for... 4 years now.

all you really have to do is cut your original wastegate control line and splice in the MBC.

The charge tube send a signal that pushes the bearing in the MBC to open the line all the way to the wastegate. This causes boost to come on sooner and sharper because the WG isn't constantly bleeding the boost off til it gets to full pressure.

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flosho · Posted: Thu Feb 12, 2009 6:08 am Post subject:

Also, one thing that you may have to do, is hog out the ports on your MBC, regardless of the type. Our cars have huge wastegate feed lines, so if we restrict it, like with a mbc that has small ports, you will see your boost spiking. I've read a number of people on the forum found that out, as did I. I too the drill to the nipples/ports on the MBC and it was fine.
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bass gt · Posted: Thu Feb 12, 2009 7:13 am Post subject:

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

The MBC i have has no ball and no spring...its a cone type...i've made a section drawing of it. The inner diameter of the lines is aprox. 4mm. What is the inner diameter of the WG control line?

The main problem i see is the lines cloging up with oil from the intake...thats why i dont want an inline MBC...with a Tee MBC the chances of cloging the lines and overboosting are smaller.
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