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On 17 Jun 2004 at 21:06, Steven Ayres wrote: > JimA=> the only way around it is to supercharge the intake. > > Would that really do it? The proportion of oxygen to air volume remains the > same, so wouldn't you just have more of the same rich mixture? It sounds like you're under the impression that carbs just inject a fixed amount of gas for a particular throttle opening. Both the FI and carbs attempt to meter fuel into the airstream in proportion to the amount of air entering. As you go up into thinner air there is, by necessity, less air that can enter, and the fueling system admits less gas to maintain the ratio. So the engine power must go down simply because there is less fuel + air. In reality, carbs are not particularly good at metering fuel properly, so the fuel/air balance also gets out of whack when a carbed car changes altitude. Our FI is much better at this since it is actually looking at air pressure. VW made an altitude compensator for carbs which attempted to make up for this flaw in the Solex carbs, but I've never seen one. Both systems respond to total air intake, so this would not work at all if the oxygen/air ratio changed, but we are fortunately safe here. Supercharging, even if it only brought the intake pressure back up to sea level, would keep our outputs constant, at least to whatever altitude the supercharger wimped out. Note that for purposes of this discussion, turbocharging is just one form of supercharging. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org