924Board.org

[-nick]

Just wondering if I can get rid of my boost gauge if I have a display of the manifold air pressure? I would assume that a boost gauge fitted to the manifold side of the throttle body would read exactly the same as the MAP sensor, but it pays to check. Can anyone confirm?

nick

[Peter_in_AU]

a standard GM MAP sensor outouts a voltage from 0v to 5v. The meaning of a particular voltage depends on the range of the MAP sensor.

For 1 bar MAP sensor (used for NA cars) 0v = "full" vaccum and 5v = atmospheric pressure.

For a 2 bar MAP sensor (used for turbo cars) 0v = "full" vaccum and 5v = 1 bar of boost.

The rate of voltage change of the MAP sensor should be linear so for a 2 bar sensor 2.5v should be about atmospheric. There are some MAP sensors out there that output a resistance rather than a voltage but the GM sensor is the standard.

Bottom line, an electronic boost gauge connected to a MAP sensor connected to the intake plenum should give the same reading as a mechanical boost gauge connected to the plenum.

Take a look at http://www.diy-efi.org/gmecm/component_info/sensors.html
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[-nick]

Thanks Peter,
The megasquirt software gives a readout of MAP in kpa (I imagine I can have it convert to psi/bar/whatever). I just wanted to make sure it is a reliable tracer of boost.

Now I've just got to figure out how to rig up a display monitor in the dash for all the engine gauge info and avoid looking like the fast and the furious

nick

[Peter_in_AU]

this shows the basic problem with the whole metric system - it's too easy

0 kpa = 0 bar, 50 kpa = 0.5 bar, 100 kpa = 1 bar etc.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you