Mech vs elect boost gauge...novice question
 

Okay...the tread about "whats the best boost gauge" had me thinking and asking questions but it sort of died out and really doesn't describe very well my questions. Yes, I would like to know what is the "best" boost gauge but I really want to understand how they work...so here is my question:

Does the electrical boost gauge suffer longterm from the heat in the engine bay (i.e. the wiring harness/etc) vs the mechanical tubing?

Please tell me more about why I do/do not want PSI vs BAR readings?

and really stupid question: the needle is at 0 but why do the numbers go up and also down? does the needle swing above 0 and below 0? If so, what are the numbers below zero represent...??

Sorry for the long thread...

As far as PSI or bar. Its pretty much up to your preference. PSI is more common here in the states but its not really hard to remember a conversion from Bar to PSI. After a few times of calculating you'll just rmeber off the top of your head what bar = what PSI. Its some thing like 1 bar = 14.7PSI or something close to that.

The numbers above zero represent boost pressure. The numbers below zero represent vacuum. I'm not really sure what vacum is though. Would someone care to elaborate on that?

I think that electric gauges are generally a little more accurate. They are more responsive than a mechanical. and the peak hold and playback modes that are available on some gauges is very nice.

Vacuum: The quick and dirty explination.

All engines create vacuum at idle. Essentially when your car is idling, your engine is acting as an air pump sucking air in through the intake into the engine. Its free power, which is why alot of components run off of engine vacuum, (e.g. Brake booster, all those annoying solenoid check valves etc.)

Where do the electronic boost gauges hook up? The ECU? I know that the mechanical ones hook up to that nipple on the manifold, but I can't think of anywhere to hook up the electronic ones :(

The electric boost gauge still hooks up to the manifold. You run the vacuum line to a pressure sensor that you place in your engine compartment. You then run the electrical line from the pressure sensor through the firewall. Electrical gauges are nice because they offer the warning, memory, and peak features.