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A thought re: lean conditions at low RPMs (long)
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Posted by Alex (more from Alex) on Fri, 14 Dec 2001 11:22:13 Share Post by Email
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I'm one of those who is having trouble running higher boost in my 9kT due to "lean conditions" below about 3500 RPM. Once I get above that, it seems to do fine.

I think everyone may be judging this one a little too fast. Is it really lean conditions that are causing this problem? 18 PSI @ 6000 RPM will use more fuel than 15 PSI @ 3500 RPM. I can do the former, whereas the latter I cannot.

I think the turbo may actually be surging. For those of you who are unfamiliar with surging, I'll give a brief explanation:

A turbocharger is an air compressor. It is powered by your exhaust (with a turbine in your exhaust), and uses a compressor in your air intake to pump more air into your engine. When a certain pressure is achieved in your air intake system, the wastegate will open, allowing some of your exhaust to bypass the turbo so that it does not provide power to the turbo. This will slow the turbo down so that it isn't continually raising the boost. However, if the wastegate doesn't open and the turbo is allowed to spool up uncontrolled, it will compress the air until the exhaust coming out of your engine is no longer providing enough force to compress the air further. At this point the turbo wheel will slow down from the resistance, possibly even stop, SOMETIMES even spin backwards a little as the air in your intake system tries to escape. Once the pressure does go down (either escaping the way it came in, or used up by the engine), the tubro will spool up again and repeat the process. Obviously, this not only causes unpredictable intake pressures but terrible back-pressure in the exhaust system as well.

Could this be what's happening? Questions/comments?

posted by 152.113.19.1...
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