Re: Dr. Boost...more MBC discussion... - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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Re: Dr. Boost...more MBC discussion...
Posted by Dr Boost (more from Dr Boost) on Sat, 6 Apr 2002 15:44:39
In Reply to: Dr. Boost...more MBC discussion..., Richard P., Thu, 4 Apr 2002 08:44:18
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Hi !
Dear Richard, and all the others !
Let me give you a short lesson in knock control.
In todays modern hi-compression turbocharged engines, knocking, (detonation) is a normal condition.
It is NORMAL that the engine knocks, or at least close, very close to the limit.
Sometimes, on "the other side of the limit", and the knock control function comes into action.
A 9k Aero engine with CR: 9.25:1 boosts 1.08 bar, this is something that was considered as impossible some years ago.....
And, a 9-5 Aero can hit 1.4 bar under some conditions. (wow)
Early Turbocharged engines had low compression, to avoid knocking, sine they had no or quite simple "control systems".
Today, we´ve milled down the heads...and boosts even more !
With exellent combustion control, it´s possible.
It is a matter of balancing on this fine line between happiness or disaster.
Unfortunatly, too few people understand this.
When the engine starts to knock, depending on the operating point, we use different remedys, retard ignition timing, and if needed fuel enrichment.
If the engine still is knocking it´s time to reduce the level boost.
With a MBC, the ECM cannot reduce the boost, which can result in severe damage to your hardware.
Sometimes it takes time before the stuff breaks, if you are fortunate it takes alot of time.....
Some types of knocks can be heard by the human ear, some you just don´t hear, AT ALL.
Usually they are of the kind that really makes your lift difficult.
So, please do not trust your ears.
We use special equipment to listen to the engines at the labs.
posted by 195.67.248...
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