Re: ECM for forced induction

[Daniel Houlton <houlster@user1.inficad.com>]

Jim and Sharon Brady wrote:
[Charset iso-8859-1 unsupported, filtering to ASCII...]
> Ludis,
>     So the 2-bar MAP sensor simply has the capability to read twice the
> range of a regular (1-bar) MAP sensor?  Is this because with forced
> induction instead of low vacuum or zero vacuum you have positive pressure?


You have both.  1 bar is 1 atmosphere is 14.7 psi (roughly).

Remember, the MAP sensor reads Manifold Absolute Pressure (this is 
downstream of the throttle butterfly).  In a NA engine, you have pressures
from vacuum (with the throttle closed) to 1 bar (with throttle wide open).

With say 14.7 psi of boost, you have from vacuum (throttle closed) to 2
bar.  (14.7 lbs of boost == 2 bar or 29.4 psi *absolute* pressure)

With say around 22 psi of boost you have from vacuum to 2.5 bar, etc.

For whatever boost you run, you need a MAP sensor that will cover the
range from vacuum to that boost level at a minimum, and a computer that's
calibrated for it.  

All MAP sensors (1 bar, 2 bar, 3 bar, etc.) have roughly from 0V to 5V
outputs so the ECM needs to know which one it is.  i.e., a reading of 2.5V
could mean you have in the intake manifold roughly .5 bar, 1 bar, or 1.5 bar
depending on which MAP sensor you're using.


--Dan
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