Are they a basic Bourdon gauge with an eliptical cross section or are they a diaphram setup or something else all together?

 

Yes, most mechanical boost gauges are Bourdon tube type.


-Ted

 

great, thanks

 

The stock gauge is pure electronic.
The ECU reads the pressure sensor & generates a (weak) signal to the (sometimes working) dash gauge.

FWIW: I wired my S-AFC to monitor boost.
It showed that the pressure sensor is very reliable, so the ECU sees good values.
The dash gauge is not always accurate.

 

how do you wire the s-afc to monitor boost? I may be interested in doing the same.

 

Use one of the other monitoring wires like RPM or Throttle.

 

Instead of tapping into the TPS signal at the ECU with the SAFC TPS signal wire... you tap the TPS signal wire from the SAFC into the wire coming from the BOOST sensor at the ECU.. Now your SAFC is seeing the voltage from the Boost sensor instead of the TPS

The SAFC will then learn the max an min voltage points from the boost sensor and display your relative boost as % throttle on the Face.. (you just have to remeber that its boost, not throttle) SOOOoo 0% throttle will actually be somewhere areound 20inHG of vaccume and 100% throttle will be around 8.0 Lbs of boost. (assimung you have your boost controller at 8 PSI)

I think at idle, my car used to show around 8% throttle and 0% when off the gas and decelerating and around 45% when at 0PSI, but you will have to watch the boost gauge to determine where yours corresponds

You can then set up your SAFC to add or subtract fuel based on % throttle (boost) as a function of RPM and you will actually be setting it up to %boost. Interestingly.... this is exactly how you program a haltech!!!!!! at this rpm, at this load, you are going open the injectors this much!!!!

This is the best way to set up a Turbo car with an SAFC, IMO and about the only accurate wat to set up an s4 because the s4 TPS only goes to about 30% throttle then maXes out.

 

FC turbo stock boost sensor is a "2bar" MAP, so it should be about 15psi at 100% or 5.0VDC.


-Ted

 

yeah... I edited my post to reflect that 8 PSI is about the limit of the stock computer without an FCD. * psi is around 3.5 volts. But if thats the highest the SAFC ever sees.. it will "learn" that is 100% of the voltage range that it sees and display it as such.

ANOTHER POINT.. if you are using an FCD.. You want to tap a wire into the boost sensor pressure out BEFORE the signal reaches the FCD.. That way, the SAFC will see the full boost range and then you can add more fuel as boost increases.

If you tap in AFTER the SAFC, the FCD will cut the voltage and flatline it at around 3.6 volts so that the ECU does not hit fuel cut.. This will also not let the SAFC see any higher readings than 8 PSI..... and therefore, not let you add anymore fuel past that point either.

 

So 5V is 1 bar to the factory pressure sensor?