Barometric Correction - Does location of sensor matter?

[jsdevel]

I've been looking at making the MapDaddy upgrade, and am wondering if changes to cabin air temperature would affect the barometer readings very much? Would it be better to have a hose to the outside air instead?

I would imagine with my AC on, the air inside the cabin could make the air denser, which in theory would create more atmospheric pressure; albeit very little as there isn't a lot of air to make a difference.

[racingmini_mtl]

Unless your cabin is tightly sealed, any temperature induced change in air density will not be accompanied by a change in pressure; the cabin pressure will be equal to the outside pressure. Air will leaked in and out of the cabin to keep pressure equalized.

Jean

[jsdevel]

Got it. Thanks!

[brianj5600]

I was thinking of measuring close to the air filter. As a car's speed changes, so does the pressure under the hood. I hope to log that and see how bad my filter location is at speed. I need more ADCs though.

[jsdevel]

I was thinking of measuring close to the air filter. As a car's speed changes, so does the pressure under the hood. I hope to log that and see how bad my filter location is at speed. I need more ADCs though.

If I'm not mistaken, Baro is to calculate resistance of the exhaust gas as it's exiting the engine, amongst other things, air pressure and ease of air entering the engine being one of them. Ideally you'd probably want the sensor located in a stable place like the cabin to avoid turbulance or other factors skewing the readings. (This is me as a noob speaking theoretically).

[brianj5600]

I would be very surprised if the pressure at the exhaust exit is not affected by speed too. My exhaust exits through the rear valance a couple inches above the bottom of the valance. That should be an area that pressure drops as speed increases. Pressure in the interior changes too. Roll down the windows on the interstate and after a few minutes and your ears will let you know about pressure changes.

[jsdevel]

Right. I wonder if there is positive pressure in front of the car and negative pressure behind it?