JohnB

We have the dyno graphs up on our web site of a recent trip to the dyno with an STI 8 with a 3" exhaust (no cats) and a stock STI 8.

110kw vs 70kw @ 3700Rpm

145Kw @ 6000Rpm vs 132Kw @ 5800Rpm

Only mod was the exhaust, no boost controller or such like YET.

Check them out on www.subaruclub.co.za under events, Dyno days, All results, sort by model under MY03 STI 8. Also interesting what happened on the STI after 3800, seems to have spiked and then pulled back, any comments on what could be causing this?

BugEyed

Is this the point at which the AVCS kicks in? It certainly looks odd, and is presumably fueling/timing/boost/airflow related.

For ease of use, here are links straight to the graphs:

Standard

3" exhaust

Duncan

sti03

A Company in Australia called APS fitted a Turbo back 3" exhaust on a stock STI03 ( no ECU upgrade ) and found that the booost spiked up to 23psi at certain rpms which is very risky

hades

IMHO, that looks just like boost spiking. I believe it's caused primarily by the wastegate duty cycle being mapped to overcome the restriction caused by the exhaust (step forward JB or others to tell me I'm spouting rubbish!). Remove the restriction, and the boost overshoots. An analogy is pushing a wardrobe hard - if the wardrobe is suddenly disappears, you'll shoot forward and fall over.

Common on STi7s with decat exhausts on - the standard fix was to increase the restrictor size to about 1.2 or 1.25mm in order to slow the spool up a bit. Other option is a proper remap which alters the wastegate duty cycle.

john banks

Sorry was in France. From the 3" graph it is obviously overboosting and probably detting with it with that sort of spike. Lots of previous threads on this for the searching.

Also look out for boost creep. Very dodgy because no active knock control in the area where boost creep occurs, very high EGBP, high charge temp, risk of turbo overspeed, pollution of the fresh charge with exhaust gases, detonation. Pretty bad news.

sti03

would a cat back exhaust ( cannone type ) still spike up the boost or lose power on the 03STI?

STi M'8

I experienced boost spiking around 24psi during first test of a 2.5' single cat plus Blitz 3' center and BB on my STi03...
A 1.1mm restrictor (instead of 0.9mm) solved the overboosting issue with a maximum 1.25b in 6th gear now, without any noticeable slowing during spool up.

Did any remaper (such as JB) compared std STi7 and STi8 WG solenoid duty tables ? I've got the feeling they are slightly different.

EMS

Only small changes in the maps (mainly to the knock learning tables), the WG maps are the same!

Mark.

JohnB

Thanks for all the advice guys, to get this care back to a relatively "safe" state what would you suggest?

Would changing the restrictor be sufficient or should we be looking at either a remap or a boost controller of some sorts?

Regards

JohnB

EMS

A proper remap is the best thing you could do. If you don´t want to spend the money you could change the restictor to about 1.2 mm (standard restrictor size for the "normal" WRX) to avoid boost spikes when the turbo is spinning up. Furthermore look at your boost gauge if you drive in 5th and 6th gear at high revs (above 6.000 RPM), the boost shouldn´t exceed 1.0 bar to keep it safe!

Mark.

sti03

would just a rear muffler still cause spiking on the STI8

WREXY

Where is JB by the way? Haven't seen him post for quite a while now.

[Edited by WREXY - 4/5/2003 12:03:24 AM]

john banks

Don't have the STi 8 ROM files so don't know. I could get them if needed but I haven't done an STi 8 yet so not needed them. Maybe Bob or Pat or Ecutek would help.

[Edited by john banks - 4/6/2003 10:29:06 PM]

STi M'8

Don't think so.
If both cats remain, you'll still have an important turbo back flow restriction.

[Edited by STi M'8 - 4/9/2003 9:12:06 PM]