[Diy_efi] Re: Question about speed density, etc.

[Erik Jacobs]

i've been lurking for a while.. forgive me if I'm not as smart as some of
the rest of you...

> On most cars, that is the
> only way to control engine power.  Throttling the flow, by definition,
> also reduces manifold pressure.  For a given volume flow of air, which is
> fixed by the engine's displacement and the rPM, the only way to control
> power is by varying the density, which you do by varying pressure
> *behind* the throttle body, in the manifold.

umm... but I don't think the physics behind this make sense, or maybe I'm
misunderstanding them... but if the wastegate is pinned, the turbo is
forcing a fixed amount of air out of the compressor and through the
system... and assuming that for one instant all valves are closed at the
same time, it seems that the intake system would be charged to the same
pressure, as long as the throttle plate is open a bit.

actually.. i think i'm beginning to understand... is it similar to water in
hose?  like how you pinch off the end of the hose with your thumb and the
pre-hose pressure is different than the post-hose pressure?  I'm having
trouble with the fact that the manifold pressure is different than the
system pressure...

sorry I guess this is OT...


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