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Old 03-17-2003, 09:39 PM   #1
Scooby Newbie
Member#: 33468
Join Date: Feb 2003
Location: Portland, OR
2004 WRX STi (soon)

Default STi Performance limitations

This is a noob question I know but...here goes.

How will the drive-by-wire affect the ease of upgrading the STi. I'm not sure, but I would think that if you put a boost controller and upgraded the BOV, it wouldn't do to much due to the fact that the ECU would see the extra air flow and reduce the throttle to act as a saftey.

I have learned by reading these boards that the WRX runs right on the brink of knocking and that is how they get so much out of these engines. I assume the STi will be the same way. I am I just going to have to wait until they have some decent aftermarket ECU's to start upgrading? I realize the importance of good engine management but, how much does that usually cost? Will the cost of engine management be more expencive for the STi than the standard WRX?
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Old 03-17-2003, 11:30 PM   #2
Scooby Guru
Member#: 456
Join Date: Oct 1999
Chapter/Region: NWIC
Location: Redmond, WA, USA
2008 Forester XT
Steel Gray Metallic


You don't state what you want to improve or how much power and reliability you want.

Replacing the STi ECU would be problematic --- you'd have to read the throttle position sensor (the one located on the throttle body) as well as the accelerator position sensor (the pedal) and control the stepper motor that powers the throttle butterfly.

Don't forget running the AVCS as well....!

Most likely a piggyback solution for ignition, boost and fuel mapping, but personally I'd be pretty nervous about messing with such a sweet setup.

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Old 03-17-2003, 11:33 PM   #3
Scooby Specialist
Member#: 25247
Join Date: Sep 2002
Chapter/Region: TXIC
Location: I B Insane PGR2 XBOXLive
1999 Coupe L


There are no limitations to the STi performance. except the

SRT-4 is faster.

Sorry had to. Oh better use one the green ones
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Old 03-18-2003, 03:32 AM   #4
Scooby Newbie
Member#: 33468
Join Date: Feb 2003
Location: Portland, OR
2004 WRX STi (soon)


Well, I would like to see the STi get 350 to the ground some day, but not right off the bat. I would like to see what mods will be done easily without having to getting into a lot of technical stuff. One thing is that from the pics that I have seen, the exhaust doesn't seem to be over 2.5" and has alot of stuff before the last cat, so it would be safe to say that a 3" turbo-back exhaust would add 10-15hp (maybe). But after that...I am lost on posible effective mods.
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Old 03-18-2003, 04:04 AM   #5
Scooby Specialist
Member#: 11218
Join Date: Oct 2001
Chapter/Region: SCIC
Location: Orange, CA
2005 Legacy GT Wagon
99 Miata, 91 Miata turbo


My impression is that in stock form/tune, the WRX is not on the brink of knocking. That's why tuners are able to get 30 or 40 whp on a stock wrx. They are getting closer to the limit.
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