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Re: [T3] Hill Climbing and power loss.

On 18 Jun 2004 at 10:26, Steven Ayres wrote:

> JimA=> they are usually set up to give a particular boost
> => above the current relative pressure.
> Exactly. So the differential between sea-level and mile-high intake air
> density remains, whether supercharged or not. The question is whether this
> differential affects fuel mixture under supercharged conditions the same way
> it does with normal aspiration, assuming a real-world supercharged system.

With a really good carb, there would be no change in the fuel/air ratio as you 
drove up and downhill. I THINK the venturi principle really has the potential 
of measuring air mass, not just air volume, so it should be possible to make 
such a carb. OTOH, I know that few carbs are this good, so adjustments have to 
be made.

> Obviously if you add air to a given carb at high altitude, you'll compensate
> for lower local pressure. But a supercharged system involves more than
> adding a blower to a carb, no?

In principle, I think all you have to do is add the blower, but certainly there 
are problems you get into. I think they are not so much problems related to a 
major change of principle as they are problems related to the fact that the 
carb is no longer running within a range where it really works at all well.

For example, if you doubled the air density, then the velocity thru the venturi 
would be halved for the same engine intake conditions, but at half velocity 
this carb might not pull any gas at all.

Maybe I'm just completely wrong about this. But I was under the impression that 
a carb actually responded to air mass, it was just that its response was 

The D-jet, as well as all of the later systems, are all designed around 
different ways of measuring the flow of air MASS, and they all do it rather 
well, so they are not bothered by changes of altitude any more than would be 
expected due to the fact that less fuel + air can get into the chamber.

This leads me to a request for the Hershey Invasion. Would it be possible to 
have some kind of blackboard or whiteboard or something similar there? There 
are just so many things that can be asked and answered better if we can draw 
pictures and graphs.

Jim Adney
Madison, WI 53711-3054

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