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As I understand it - and please correct me if you reckon I'm talking tosh, which is not unknown - the boost is restricted on all 200bhp automatics to help reduce max torque from 323 Nm to 294 Nm, to preserve the gearbox.
According to Saab's brochure, maximum boost on a 1997 automatic (like Nahum's and mine) is 0.81 bar (about 12 psi) compared with the manual's 1.0 bar (14.5 psi).
Max boost on a manual Aero is a little higher, about 1.08 bar/16 psi. But the 234R engine in the manuals also has a larger turbo than the automatic (Mitsubishi TD04 rather than Garrett T-25) and different ECU software. This engine specification also found its way into the 1998 CSE manuals, which is why people like them so much. Result is 225 bhp and 342 Nm.
The automatic CSE and the automatic Aero engines are exactly the same (the 234L) in all respects and that includes the ECU.
However, when you put an automatic car into "drive" the ECU receives a signal from the gearshift that tells it to restrict boost. The signal goes to pin 14 on the ECU via the famous orange wire. Removing the equally famous fuse 9 cuts the supply to the gearshift switch, so the ECU thinks it's in a manual car and allows more boost.
I pulled the fuse this afternoon, when driving back from London and before reading your post. Could only test in third gear for obvious reasons!
I found that with the fuse in place, the needle on my gauge would flip up to .8 bar, hold for a while at .75, then drop back to about .6 bar at 5,500 rpm. The change into fourth then put the boost straight back up to .8 bar.
With fuse 9 removed, the needle flipped past 1.0 bar, stabilised at .9 and then cut back to about 0.7 by 5,500 rpm.
Maybe the car isn't perfect, maybe the gauge under-reads - that's just my experience, today. But this ties in with the effect on my previous '93 CSE, on which I ended up just snipping the orange wire. So it's definitely not an Aero-specific thing - quite the reverse, in fact - though the precise effect is sure to vary from car to car. Whether anyone wants to do it and risk nuking the gearbox is another matter.
Out of interest, max boost figures for the 1993 200bhp engines were 0.94 bar manual, 0.78 automatic. 2.3 turbo compression ratio was 8.5:1 in 1993 compared with 9.25:1 in 1997. All figures UK spec but I'm pretty sure they apply across the board.
Finally, I found my 0-60 time was very roughly 8.5 seconds this afternoon. 14 degrees C, Shell Optimax fuel. That's not far off Saab's claimed 8.1 seconds, so its rubber band still seems to be working fairly well.
1997 2.3 fpt Anniversary automatic, Aero suspension (but no Aero seats or badge...)
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