[Vwdiesel] Fueling and turbo boost

[hwy9fergs at comcast.net]

Andrew said,   
I imagine that if messing messing with the aneroid spring perch and cone 
rotation one can achieve a situation where more air is being pumped into the 
engine by the turbo than the pump is pumping fuel in to adequately burn.  I 
imagine 
there would be resultant losses in pumping that additional air through the 
engine.  
I'm not giving up on you yet Andrew.  The part where you say "more air is being pumped into the engine-than the (fuel) pump is pumping fuel to adequately burn" is why I know I didn't do a good enough job explaining it. The concept of the way the turbo provides the boost is still needing some clarification. Also the way diesels combust the fuel.  Much as with our jet engine, there's a compressor and turbine in our little turbos on these cars. One shaft runs between.   The thing with the turbo is that it can't pump more air if you aren't increasing the fueling, because the turbine directly drives the compressor. If your fueling drops off, so will your manifold pressure. The main important point is that the more air is better in one of these engines. That's what Svend is talking about, with Bunny Bondo, turbo singing along, LDA disconnected, getting fabulous smileage.  With the LDA out of the loop, no way you're going to overfuel. (also no way to go very fast either) But more importantly, no way you can have too much air and hurt the combustion. An overabundance of air will mean more complete combustion. When you talk that way it means you are thinking GAS engines again, because if you go too far away from stoichiometric, (14.7 to 1) leaning your (gas engine) air fuel mixture too much, that's when you can hurt the combustion and decrease efficiency.  Go yet a little farther lean than that, and the spark plug can't fire it at all!!  Anyhow, back on the turbo subject, they have it worked out pretty well on the geometry of the turbine/compressor.  The turbine induces some resistance to exhaust flow but makes up for it by providing more air for the combustion. Under normal circumstances the turbo should provide a slight overabundance of air for combustion. It's a balancing act.  They design them for a given engine to provide the right amount of boost without overdoing and creating too much back pressure.  If your turbo is not spinning as freely as possible, or the blades are worn and gunked up, or the exhaust system is partially plugged, your combustion (efficiency)can suffer because the amount of air generated for a given amount of exhaust flow decreases. Main point---more air is better with diesels.  Later Gator  Doug