Re: 200mph speedo wanted

[Sean Morris <tyndago@ix.netcom.com>]

>   I heard that the stock turbo gauge is also electrical.  How did they
> do that?

Stock turbo gage is driven off the MAP sensor . Its like a pressure
transducer.  Kind of a potentiometer that varies resistance with
pressure. The ECM sends a 5 volt reference to the sensor and from the
output of the sensor the gage is driven and the ECM gets its engine
load.

> Why are the VDO and aftermarket gauges mechanical using
> vacuum rather than electronics?  Which way is more accurate and/or
> more
> preferred?

A mechanical gage is one thing to calibrate with only one set of
tolerances. The electrical setup has 4 varying things. The  5 volt input
, MAP ouput , the driver for the gage , and the gage itself. Many more
tolerances.
Either or. How well do you calibrate ? Most people don't trust
electrical gages.  6 years in the Navy calibrating things taught me
this.

> Or is it purely a matter of cost incurred in the design of the
> gauge?

Since the MAP sensor is already used for the ECM, and the instruments
are all electrical it was probably better for GM to put in an electric
gage.Remote reading electrical gages are usually prefered to mechanical
gages, because it is easier to run wires than tubes.