Setting sensor to measure vacuum

[The Outlaw]

Hi all could someone give me a guide on how to set up a sensor to measure INHG.. I’ve just fitted a vacuum pump on my race car and would like to monitor the vacuum, I’ve a spare AV channel, a kaSensor 0 to 4 bar.. I’ll fit a barbed fittings to valve cover for sensor. Just need to work out how to set it all up on the dash manager..
thank you..

[SOReilly]

4 bar is a big range for crankcase pressure measurement, if you have 4 bar absolute crankcase pressure something is wrong.

Any channel with the data type ' Pressure & Stress' can have the display unit changed to inches mercury (inHg)

Worth noting that all channels exists as their data types base unit in the background.

Configure the sensor calibration in kPa then change the display units in your display setup or in i2 if you're reviewing log data.

Confusingly you will have to configure the sensor so that what would be 100kPa absolute is 0 and what would be 0 kPa absolute is 100. because you want to see gauge measurement but with positive values for the 'vacuum' range of measurement.

[The Outlaw]

The 0 to 4 bar Sensor is a spare I got when I bought my motec dash of a friend, is it not the right sensor for the job? I just need to measure the vacuum at idle about should be about 6 to 8” and at WOT hopefully between 15 and 18” of vacuum..

[Sean]

The 4 bar sensor will work fine, you'll just be working in the bottom 1/4 of the sensor range.
(4 bar vac is approximately 118 in /hg vac)

I have used 1.05 bar Delco map sensors before to measure vacuum. Racepak vacuum sensor on another vehicle I meddle with is 30 in/hg , which is about 1 bar.

I'd advise you measure the vacuum a fair way away from where the sensor measures, in a v8 we measure at 1 rocker cover, and pull vac on the other.

Also, and this will be very engine specific, you may find the logged oil pressure reduces with vacuum applied. On one thing I tune we see 25" at idle going to the line, and 22" through the end (electric vac pump and small engine). At full vacuum, logging shows -3 psi oil pressure. You won't see that, but be prepared to see a change.