SC -- dumb question

[Mazda Ebrahimi]

Tom Cloud wrote:
> 
> it's been a long time since I've asked a dumb question
> on this list (how do I know .... it's been a long time
> since I've said _anything_ on this list  ;-)
> 
> got to thinking:  if a nnn CID engine always pumps nnn CI
> of air/fuel per two revs, and the limiting factor that
> controls it is the 'density' (i.e. vacuum) of the air
> (i.e. throttle position), how does that work with turbo/
> super charging??  is the plenum always pressurized, or
> is there still the vacuum at low rpm's ???
> 
> [ from one who's only thought about SC and TC ]
> 
> Tom Cloud <cloud at peaches.ph.utexas.edu>

Hi Tom,

As long as the throttle body is a restriction, it causes a pressure drop 
across it.  Assuming you are looking at a blow through setup, manifold 
pressure is determined by two factors: 1- pressure rise caused by 
turbocharger / supercharger, and 2- pressure drop across the throttle 
body.  When 1 > 2, you have boost pressure, otherwise you have vacuum.

Best Regards, Mazda