I've read many a time that the most destructive knocking is inaudible (would it be redundant to say "to the human ear"?) Which is to say, no, if you hear knocking, it's too late! This is why Saab took such pains with it's long development and honing of the APC/Trionic system. Sure, you might find a way to run the gauge on up into the red, but you do so at your own risk.

Here's my real-life horror story: One cold February morning long ago I'm charging up a pretty good hill on an open stretch of highway in my 900 that I've tampered with (tweaked that wastegate rod a bit, I did). Ran great in the summer, and even better as the weather got cooler. So here I am charging up this hill in 5th, at full throttle, boosting like an Alabama football fan+, when all of a sudden I hear not just a knock, not just a rattle, but a deep, VERY LOUD, bone-chilling hammering. It's like a panic stop: You let off the throttle immediately, but immeiately is a long time in human reaction time. Long story short: The engine survived and I shortened the wastgate rod that evening. I was lucky. I don't ever, EVER want to hear that sound again. The noise that I heard that morning would have broken a rod, a crankshft or a piston in most engines. Saab engines are unbelieveably tough. But let's not make a habit of asking for miracles ...

Bottom line: You won't hear it until it's too late, and your engine will be lucky to survive if you go too far. A properly tweaked ECU is fine, coupled with a 3" exhaust system (or at least a 3" downpipe). But screwing around with the stock system, trying to make it run the boost gauge in the red, is not a real wise thing to do.


posted by 206.72.2...

• Viggen BOV hooter valve allows full boost into red, aerobot, Wed, 14 Aug 2002 05:02:29
  • Soujds like you're overboosting, Quasi, Wed, 14 Aug 2002 12:37:18
  • Question on boost into the red zone..., Joe98, Wed, 14 Aug 2002 09:23:52
    • Re: Question on boost into the red zone..., Quasi, Wed, 14 Aug 2002 12:40:52
      • BSR re-mapped ECU..., Joe98, Wed, 14 Aug 2002 13:27:45
        • Forget the turbo ..., Quasi, Wed, 14 Aug 2002 23:31:57
          • Re: Forget the turbo ..., Jim Behan, Thu, 29 Aug 2002 12:44:16
        • You will find that after the initial few weeks running, jj, Wed, 14 Aug 2002 14:58:55
          • Hey, JJ..., Joe98, Wed, 14 Aug 2002 15:59:10
            • I do not have a 3" exhaust, I do have a Saber cat-, jj, Wed, 14 Aug 2002 17:44:23
      • Quasi, Will knocking be very apparent?, aerobot, Wed, 14 Aug 2002 13:03:35
        • In a word: No, Quasi, Wed, 14 Aug 2002 23:49:35 <-- Viewing This Message
    • If I remember correctly then ....---->, matt 94 aero, Wed, 14 Aug 2002 10:36:42

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