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Old 05-19-2004, 05:16 PM   #1
Scooby Newbie
Member#: 59227
Join Date: Apr 2004
Location: MD
1998 Legacy GT
Black w/ gold pearl

Default quick question on wasegates

ok, do wastegates keep the boost where it should be all the time?? I read someone had a MBC and in 1st had 8psi, 2ng gear had 10psi 3rd 14psi or so..was this caused by the MBC?? why was boost affected by the gear he was in?? wouldnt a wastegate with no controller stay where it is suppose to??

Ok, I found springs, but how do I know which to get?? They have 38mm 40mm and 46mm. How do I know what my wastegate is??
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Last edited by commador; 05-19-2004 at 08:01 PM.
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Old 05-19-2004, 09:03 PM   #2
Scooby Specialist
Member#: 43958
Join Date: Sep 2003
Chapter/Region: MWSOC
Location: ft. wayne indiana
99 RS Asphalt-01RS
Dirt-01 Forester swapped


Wastegates are suppost to keep the boost steady and at a desired pressure determind by the spring in it.

Usually, some electronic boost controller can vary boost by gear but they are expensive. A manual boost controller cant do that unless it is a two step solinoid, and even then you need to flip a switch to activate it.

I believe you are refering to boost creep but that is generally in forth and fifth gear. I dont know of that extreme of a case were the boost raised itself that much by third gear, but anything is possible. If I had to guess the guy with the mbc had a vaccum leak and that was causing such a rise in boost pressure.

As far as the springs your on your own. I dont know what kind of wastegate your running to even steer you in the right direction.

If I'm wrong let me know
just trying to help
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Old 05-19-2004, 09:33 PM   #3
Scooby Newbie
Member#: 59227
Join Date: Apr 2004
Location: MD
1998 Legacy GT
Black w/ gold pearl


The wastegate is the tial one that comes with the ludspeed stage 2. I just orderd the kit so I dont have it yet. Are there markings on the wastegate to say what it is?? Oh, and the boost creep thing, is in AFI with the title "holy overboost batman!"
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Old 05-20-2004, 10:01 AM   #4
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Join Date: Oct 2000
Chapter/Region: NESIC
Location: CA
1999 2.5RSt


Tial 38mm
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Old 05-20-2004, 04:40 PM   #5
Scooby Specialist
Member#: 6271
Join Date: May 2001
Location: San Jose
2001 2.5RSTi
2007 Legacy Spec B


wastegates control the maximum amount of boost you can push. Air pressure pushes on the spring which then opens a valve to bypass the exhaust going to the turbo.

Boost controllers let you add boost by (in a way) limiting the pressure the wastegate sees thus the wastegate opening later, when there's more boost.

Another reason why your friend might be boosting less on lower gears is because 1st and 2nd gears are short gears and the the motor isn't providing enough exhaust gases for the turbo to provide enough boost.
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