Comments

• Lennart Hed said:
  

  If it’s a full pressure turbo, then max load pressure at 2100 RPM. //Lennart Hed

  -April 28th, 2008 at 9:59 pm
• eggsngrits said:
  

  I’ll take Lennart’s word for the number, but remember, that’s at full load — accelerating. If you are cruising along at the same speed, the turbo boost will not be the same.

  -April 28th, 2008 at 10:55 pm
• edusaab said:
  

  check media.saab.com, there are the historical data from big part of the models.

  As I remember, the 2.0T 185BHP the turbo boost is 0,79 for manual gearbox and 0,63 for auto, but I think this is for the B205, but few differences in terms of boost there are between both.

  regards

  -April 28th, 2008 at 11:16 pm
• Tedjs said:
  

  Some quick notes…..

  Maximum available boost pressure would be most directly related to engine load and engine speed. In addition to that you have to compensate for any turbo lag or how long it takes the compressor to reach full speed from lets say - engine idle speed.

  The ECU has the ability to control maximum boost pressure by opening and closing the wastegate (turbo bypass) on the turbocharger in response to what it ‘sees’ on the charge air pressure sensor in the intake air (charge air) pipe that is attached to the outlet of the turbo.

  For example, from a standing start the wastegate is closed allowing all the exhaust gasses to pass through the turbo. Once you start to accelerate the turbo starts to speed up in response to exhaust gas energy (turbo lag) and begins to build boost pressure. When the computer sees what it might consider to be maximum needed boost pressure it can open the wastegate to allow exhaust gasses to bypass the turbocharger.

  Full boost pressure may be influenced/controlled by a number of factors that the ECU sees. If you were using a lower octane fuel the ECU would sense uncontrolled combustion or ‘detonation’ and might lower boost pressure to prevent damage to the engine. The ECU might also request lower boost pressure when it sees high intake air temperatures as well to prevent engine damage.

  However, during cooler temperatures the ECU might allow higher boost pressures as conditions like this are less conducive to producing uncontrolled combustion. Depending on how far you press the throttle you would also determine maximum boost. Saab typically refers to this as a torque request (NOT a horsepower request). Keep in mind this is done in conjunction with ignition (spark) timing to keep the engine operating at an optimum power level without damaging it.

  Some informal testing on my 2007 Aero SportCombi showed that from a standing start that a boost reached a maximum of 6psi between 3000 and 3500 RPM and it stayed there until around 5000 RPM where boost dropped to about 4psi just prior to the 1-2 upshift. The computer most likely reduced boost (and timing) to prevent damage to the transaxle and create conditions that producing a more controlled upshift – otherwise the transmission would have ‘slammed’ into second gear.

  I monitored all this by taking a snapshot of the engine data with Tech II so I could show my engine performance class some conditions that would influence maximum boost pressure. Some of my students ‘think’ that turning up the boost is the ‘cure all’ solution to getting more power out of a forced induction engine and although that hypothesis deserves some consideration – they need to look at other factors before they decide to max out boost and blow up there cars.

  -April 29th, 2008 at 12:11 am
• James said:
  

  one of the things I love about Saabs is that despite being turbocharged they are relatively unstressed - low compression ratios and low boost. the V6 Aero 9-3 makes 255 horsepower on only 7 psi of boost - whereas a Mitsubishi Evo makes 280 on 21(!) pounds. Good for longevity.

  A good hint if you want to keep an eye on all things pressure related is to install (or in your case, have installed) a boost gauge that displays vacuum AND boost. It’s useful for keeping an eye on things and it’s inexpensive. Plus you can impress your passengers when you floor it and the needle flicks around to the right.

  -April 29th, 2008 at 3:38 am
• Talonderiel said:
  

  Tedjs, thanx for the technical aspect of it all!! I love learning a few new things from you. Having grown up with American Muscle N/A engines, the turbo is a whole new world to me. Keep enlightening us!

  -April 29th, 2008 at 4:52 am
• Brenton said:
  

  Thanks so much with all the information! I think I am going to go ahead and rebuild my turbo (the gaskets leak a little) whenever I replace the timing chain.

  Thanks,
  Brenton

  -April 29th, 2008 at 6:11 am

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