Welcome to the North American Subaru Impreza Owners Club Wednesday March 29, 2017
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
Go Back   NASIOC > NASIOC Technical > Factory 2.5L Turbo Powertrain (EJ Series Factory 2.5L Turbo)

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
Prev Previous Post   Next Post Next
Old 01-02-2004, 04:46 PM   #1
Scooby Specialist
Member#: 32576
Join Date: Feb 2003
Location: Stevens, PA
04 STI

Default Everything you need to know about boost creep

With the countless threads about boost creep problems with turbobacks on the 2.5l STI, I think this thread should be helpful as a quick summary to those planning on moddifying their STI.

Q) What is boost creep?
A) Boost creep occurs when the wastegate is physically unable to bypass enough exhaust around the turbine on the turbo.

Q) Is boost creep harmful?
A) Yes, boost creep is one of the worst problems you can have with a turbo engine. Boost creep means that there is NO way for the boost pressure to be controlled. Boost pressures in excess of 20psi!!! have been recorded on STIs with TBE before the ECU cuts fuel.

Q) What causes boost creep?
A) Installing a turbo back exhaust whether aftermarket catted or not will in almost all cases cause boost creep to a certain extent.

Q) Are there any other options to prevent boost creep besides porting the wastegate?
A) Yes, Installation of an exhaust that either keeps the stock OEM muffler or one of the stock cats should not cause boost creep.

Q) How do I know if I have boost creep?
A) If you have a full TBE, then you probably have it. A boost gauge will tell you what pressure you are at as well. Fuel cut occurs when the ECU senses boost in excess of 17.5psi for 2-3s. Fuel cut in my experience is a very violent "stutter" from the engine that resembles extreme knock, followed by CEL.

Q) What is the overboost CEL?
A) (P0244) Wastegate malfunction

Q) Is there anything else I can do besides porting the wastegate to prevent the creeping....MBC, EBC, engine management etc?
A) This problem is isolated to the wastegate only. The wastegate is a mechanical system. There are no current workarounds or "fixes" besides this. The 2.5l just flows too much exhaust through the turbo once a turbo back has been added for the wastegate to control boost. If you think of it as a hierarchy, then it should make sense.

level 1) wastegate controls boost pressure
level 2) boost solenoid controls wastegate
level 3) MBC/EBC/ECU controls boost solenoid

Using this logic, if the problem resides on the 1st level, no matter what you do on top of it, you will still have the problem. Whatever (MBC, EBC, UTEC, ECUTEK) is controlling the wastegate CANNOT prevent boost creep if the WASTEGATE is UNABLE TO FLOW ENOUGH EXHAUST to prevent boost creep. A fuel cut defender will not eliminate the boost creep problem, but it will stop the fuel cut. Your boost will still creep up to 20psi, but the ECU won't be able to tell due to the altered signal from the FCD.

Q) My car seems to boost creep when it is cold out. Why is that?
A) Ambient temperature plays a huge role in how well your engine runs. In general, the cooler ambient temperature, the better your engine runs due to the laws of thermodynamics. The colder air causes your engine to make more HP (more work under the curve with lower temps), therefore more energetic exhaust gases, therefore your car is more prone to boost creep when it is cold out. If you live in an area that does not see colder temperatures (AZ for example) too often, then boost creep may never become a problem.

Q) I want to port my wastegate. What do I do?
A) Can you remove and install a turbo? If yes, there are a couple of options. You can send it to Deadbolt (www.deadboltspeed.com) for porting, have a local machine shop port it, or do it yourself with a "Dremmel like" tool.

Some other info on porting:

(edited---to fix links, add links, and include CEL code)
(edited #2---to include temperature question)

I hope this is helpful to some people and please let me know if anything needs to be corrected.


Last edited by wgknestrick; 05-16-2004 at 07:14 PM.
wgknestrick 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
Everything you need to know about a Cutout? zacxzx Newbies & FAQs 25 05-15-2009 06:31 PM
everything you need to know about turbos dankEe Tri-State Area Forum 1 11-08-2007 05:59 PM
Everything I Need to Know about Raleigh Durham But Was afraid to Ask Cdiff South East Region Forum 5 12-13-2005 02:13 PM
Everything you want to know about cheap boost control desiwrx02 Factory 2.0L Turbo Powertrain (EJ Series Factory 2.0L Turbo) 86 03-09-2005 08:21 AM
Everything you wanted to know about the WRC but were afraid to ask rsquire_downunder Motorsports 7 02-12-2003 11:28 AM

All times are GMT -4. The time now is 05:18 PM.

Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2017 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.