Date: Thu, 25 May 2000 13:37:30 +0200
From: "Mr. 9mm" <katana1100nopsaml.com>
Subject: Re: turbo engine vs non turbo


Nathaniel Trotter Oleson <nolesonnopsamford.edu> schreef in berichtnieuws Pine.GSO.4.21.0005242359230.19830-100000nopsaminal0.Stanford.EDU... > What kind of stress does a turbo place on the engine that a non > turbo doesn't, and how does saab engineer for this? The turbo puts stress on an engine in the fact that it is being "blown" to higher performance levels. In a non-turbo config. the engine gets its air intake volume trough vacuum, the pressure in the cylinders is lower than the atmospheric pressure, causing air to flow into the engine. In case of a turbocharged engine, the turbo BLOWS air into the engine, allowing more air, more fuel to be combusted, delivering more power than a similar size non-turbo engine. The engine is by design constructed to deal with this. There is one thing, when not yet at full operating temp, a turbocharged engine is sensitive to blowing the head gasket when the accelerator is floored. Letting the engine reach it's operating temp is the message! >The turbo runs at higher temps and pressure than the non turbo, but how does saab acount for > this? It is only the turbocharger itself that runs at extreme temp's. This is simply because it is driven by the hot exhaust gases from the engine. Again, it is constructed to deal with this. The engine runs "normal" working temp's. > For instance, if I'm buying a Saab w/ an after market turbo chip, > what kind of modifications will have been done to the car and what places > in the engine do I need to look for for wear, tear, and stress? This is another story, if you start messing with turbo pressures, ignition timings, fuel injection mod's by replacing the original chip, you could gain a lot in performance, but lose a lot in mileage! This is what happens when this is done by amatuers, they simply replace the chip, nothing more, although there is a lot to do after that... Any recent 2 litre Saab engine (the real ones, not the Opel makes) can safely be tuned up to 215 hp, without real loss of reliability. The fuel economy is wasted, of course. BUT THIS NEEDS TO BE DONE BY PROFESSIONALS (read: Saab mechanics) Where to look for wear and tear? The engine should be dry, no excessive oil leaks, look for the various bolts in the engine compartiment, is there some dirt around the seatings, are the sealings in place? If the bolts start to look a bit rounded off, there has been done a lot of work on it... If the engine has been cleaned with a high pressure steam cleaner, it could be they have something to hide... (oil). A good Saab engine can maintain 300 rpm idle speed without sounding weird. Do a compression test (especially with turbocharged engines). Take it for a spin, how does it sound, look for the tell-tale blue smoke when you go abruptly off the accelerator... if yes; not healthy... the turbo could be on it's way out. -- Pros "Everything that doesn't kill me, makes me stronger." - Nietsche __________________________________________________

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