JT 3" exhaust and base boost - my findings - Saab 9000 Bulletin Board - Saabnet.com
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JT 3" exhaust and base boost - my findings
Posted by BillJ (more from BillJ) on Sun, 29 Jul 2001 12:31:22
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OK, so I have a nicely-installed JT 3" turbo-back exhaust system that rumbles along happily. From the conversations between Bill Davies and Aero Guy, there seems to be confusion over the effect this system has on base boost and what to do about it. My car is a '96 Aero with the Mitsubishi TD04 turbo, while the other two cars discussed were fitted with the Garrett T25. This is what I found after fitting the JT system (readings are according to my not-so-accurate boost gauge, but relative readings should give some indication of what is going on):
Base boost prior to fitting was 0.48 bar as specified for the '96 Aero (0.42-0.48 bar).
Base boost after fitting (with no wastegate adjustment) was about 0.38 bar.
I shortened the wastegate rod by 1.5 turns and this brought base boost up to around 0.45-0.46 bar.
I then ran three Trionic adaptation runs.
Boost under Trionic control peaks at about 1.2 bar (on my gauge) before backing off, just like it did before. I haven't seen evidence of overboost or fuel cutoff so far.
Aero Guy, are we looking for gross problems like overboost, or is there something more subtle we ought to be aware of? What problems were seen on the car in Belgium?
One observation: I haven't noticed the expected performance improvement yet, but then it is well over 30 deg C (over 90F) here today and my recent driving has been in much cooler weather. In fact, performance seems to be down, if anything, despite the boost gauge showing normal boost. I suspect Trionic is detecting knock and retarding the timing rather than reducing the boost. Does this sound right?
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