Welcome to the North American Subaru Impreza Owners Club Monday July 14, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Factory 2.5L Turbo Powertrain

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Thread Tools Display Modes
Old 01-13-2006, 03:49 AM   #1
Scooby Newbie
Member#: 100462
Join Date: Nov 2005
Location: Salt Lake City/Moab
2004 WRX Sti
Aspen White

Default Boost Controller Question

I was just looking into boost controllers (before I got my accesport realized I needed EM first) and had a few unanswered questions to take care of. It is to my understanding that the boost pressure is regulated by 2 factors: Which gear your in, and RPM (please correct me if I'm wrong). This makes it almost impossible to hit peak boost in 1st or 2nd gear. Does a manual boost controller override the computers gear and rpm regulators, for instance, woulda manual boost controller make it possible to hit peak boost in first gear or even neutral? I'm not looking to increase boost pressure. Also I have an AP on stage 1 HWG and I'm hitting 17.5 PSI. Would a manual boost controller override the AP also example: if you set the boost controller on 13 would your peak boost be 13 or would the accessport take over and boost to 17.5?
* Registered users of the site do not see these ads.
moabrox is offline   Reply With Quote
Old 01-13-2006, 01:31 PM   #2
Scooby Specialist
Member#: 56468
Join Date: Mar 2004
Chapter/Region: NWIC
Location: Seattle, WA
04 Improved STI
Dirty White


Boost is regulated by the energy in the exhaust, the amount the wastegate is open, and the amount of exhaust that can flow through your turbo housing.

Not enough exhaust flow-->low or no boost.
Wastgate closed-->uncontrolled boost
No boost control-->wastegate runs on spring pressure (~8 psi)
Not enough flow through the exhaust housing-->boost creep (boost rises, never holds steady)

You cannot hit peak boost in 1st gear because your boost control system cannot "bleed" enough boost off of the wastegate and so it blows open. It's as if you are running on "semi" spring pressure.

There a number of solutions to you needs: better solenoid for the stock system, manual boost controller, manual boost controller in conjunction with stock solenoid, separate electronic boost control.

To answer your last question, if you have a separate boost controller (not the stock) and set boost to a lower value than what the ECU is trying to achieve (your example 13 psi vs AP's 17.5 psi), then your boost will be 13 psi and the ECU will keep "trying" in vane to achieve 17.5 psi.
bboy is offline   Reply With Quote
Old 01-13-2006, 02:38 PM   #3
Scooby Newbie
Member#: 100760
Join Date: Nov 2005
Chapter/Region: SCIC
Location: Trabuco Canyon, California
2006 WRX Sedan
Aspen White


^what he said...

and, on the other side of that, if you set the MBC for higher say...18psi, you will achieve it in every gear...

but never in nuetral
Underboosted is offline   Reply With Quote
Old 01-13-2006, 02:44 PM   #4
Scooby Newbie
Member#: 100462
Join Date: Nov 2005
Location: Salt Lake City/Moab
2004 WRX Sti
Aspen White

Default thanks

Hey, thanks alot guys, I don't want to hit boost in neutral just thought it might (in theory). But mainly I just wanted a little more in 1st and 2nd. thanks again.
moabrox is offline   Reply With Quote
Old 01-13-2006, 02:57 PM   #5
Scooby Specialist
Member#: 88322
Join Date: Jun 2005
Chapter/Region: MWSOC
Location: Indianapolis, IN
2009 BMW 135i


A blocking or interrupt style solenoid will pretty much allow you to build as much boost as you want, until the backpressure itself pushes the WG open. You only need enough time for the wheel to get up to speed, which still may be a problem in low gears unless you're traveling uphill or something. There's no need for an MBC bleeder with a blocking solenoid, because you can almost instantly have atmospheric pressure in the WG control hose.

An MBC bleeds off pressure to make up for the inability of the stock solenoid to bleed enough air fast enough. If you block, there is no flow limitation because charge air cannot get to the WG spring at all. The small volume of pressurized air that is there can easily dump when the solenoid energizes. The stock bleed solenoid has to bleed a constantly refreshing volume of air from the turbo compressor even when energized.

For the cost, and if you can retune your boost map (via UTEC, AP ST, pro tune, etc), I'd start with a new solenoid. It's about $40 for a GM setup and it takes 15 minutes to install, plus tuning time. Search for "gm solenoid full diy".
Freon is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Stock Boost and Boost controller question benibarra23 Factory 2.0L Turbo Powertrain 21 06-15-2010 09:13 PM
boost gauge/boost controller question scoobaru_wagon Newbies & FAQs 9 04-30-2005 09:37 PM
manual boost controler question bttune2.5rs Factory 2.0L Turbo Powertrain 2 05-30-2001 06:26 AM
More boost controller questions.... Obscure411 Factory 2.0L Turbo Powertrain 34 05-15-2001 10:15 AM
Boost Controller Question Steve E Technical Forum Archive 9 10-11-2000 01:58 PM

All times are GMT -4. The time now is 06:18 AM.

Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.