Boost in Psi - what if your baro pressure is not 100kPa?

[Blades]

Wouldn't it be more accurate to use the function [sens.30.imp]-14.6 if your baro pressure was more like 100.5? Hell, weather.com says 30.17 inhg which is 102.15kPa.. So whats up with [sens.30.imp]-14.5? I have a feeling thats why I read fractions of a psi when I scan with the engine off..

[5_Liter_Eater]

I run ([PID.11.MET]-[PID.2340.MET])*.15.

(Manifold pressure - Baro) in metric converted to PSI. I believe someone said that baro was not really a true sensor though.

[redhardsupra]

baro is a number that computer sets at startup, and then updates at WOT. it basically saved them having one more sensor, kinda silly but it works

[5_Liter_Eater]

What do you mean updates at WOT? Since I have a 2 bar MAP and my WOT is not atmospheric is that skewing my fake baro sensor?

[redhardsupra]

it's something i noticed once completely by accident when playing with a LS4, i never tried it on any other platform so who knows, but yea, basically i drove up a big hill, went WOT, and the logged BARO dropped value and it stayed that way until i drove down the big hill and went WOT when it changed again. i guess this is gm's way of saving cost (bailout my ass...)

[5_Liter_Eater]

Hmmm. I'm sure mine doesn't do that or the baro would be ~165 kPa. I did notice how it is different on different logs and stays static troughout the log.

Good info.

[Blades]

Is this why the Cobalt SS-SC/TC has a separate baro sensor?

[redhardsupra]

probably, as that would solve the problem

[Blades]

Yeah, the tune file even has DTCs for Baro sensor performance. I'm pretty sure the MAP sensor I'm using is a baro sensor for the Cobalt - in fact, I'm certain. The MAP sensor for the Cobalt also has IAT..

So whats the reason for using a 2 bar sensor as a BARO sensor?

You mention 'problem' - but is there really a problem? When we turn the key, it gets the baro press. Is there a fix in the 2bar OS that prevents it from sampling the sensor for a baro reading when a boosted car goes WOT? Or does it just record a max of 105kPa? I doubt thats the case.

I'm sure we could install a separate baro sensor - the PCM seems to report a more accurate (in terms of decimal precision) reading of the MAP sensor when the baro sensor (not pid) is logged. Don't think its necessary or beneficial.

[Baldturbofreak.com]

If your running the 2 bar op system, wouldnt it sample the baro at whatever baro is? If Im not mistaken the tabels and MAP sensor transfer are written for the 2/3 bar map sensor respectively. so it understands that ~2.5v is 100kpa.

[redhardsupra]

i doubt that this stock strategy intended for a NA motor with 1bar MAP works correctly with a 2/3bar MAP. computers dont understand 100kpa, they only understand voltage that happens to correspond to some pressure value that's meaningful only to humans.

thus, if the stock 'MAP doing double duty as BARO' strategy is in effect, and you go changing the MAP sensors about, what would probably happen it would set the BARO value to the voltage that the MAP was showing when you gone WOT. so if you're running 0.5bar@gauge on a 2bar MAP, and you go WOT, BARO will show somewhere around 3.5v probably, which depending on how BARO gets interpreted might take on different values.

This is a good exercise for anyone with a normal NA platform converted to 2barSD. log MAP, BARO, and MANVAC for good measure, and go WOT, let's see if they make sense separately and together. This would tell us a lot about how BARO is implemented, and whether we should do something special for the 2/3bar conversions.

[striker754]

I have a 3 bar OS, these are my observations from the 3 bar OS and my logs:

The car picks up BARO from the map sensor in the time from key on to start. It doesn't change throughout the entire time the key is on.

MAP - baro will give you a true boost reading for a custom PID. Alot of people just say 14.5 because they live near sea level, blah blah, no one takes into account people in higher elevations

[driftnpow]

baro readings are very close to what is shown by the beauro of meteorology for melb in my vehicle scans, ive got scans in round the suburbs and up in the victorian alps, happy to provide scans but yeah its mainly to offset fueling according to the current air thickness (baro pressure) - lower atmospheric barometric pressure equates to less oxygen and visa versa
so its not so much responsible for airflow as your maf and map/airload is responsible for.
so unless you love driving to high altitude for competition wouldnt worry all that much.

[Blades]

So.. if the baro pressure reported elsewhere (like weather.com) is 30.2 inhg, then 14.5 isn't really an accurate # for me. I rarely ever see 29.53 (1 bar) for baro readings from external sources.

[WS6FirebirdTA00]

So.. if the baro pressure reported elsewhere (like weather.com) is 30.2 inhg, then 14.5 isn't really an accurate # for me. I rarely ever see 29.53 (1 bar) for baro readings from external sources.

What you see on the weather is a corrected value, it is not the actual atmospheric air pressure. We have barometers setup throughout our lab which never really go above ~14.4-14.5 PSI on average, around 29.4 or so in-Hg, so that is not something you can really go by. I believe it is an altitude correction factor that changes it.

[12secSS]

What you see on the weather is a corrected value, it is not the actual atmospheric air pressure. We have barometers setup throughout our lab which never really go above ~14.4-14.5 PSI on average, around 29.4 or so in-Hg, so that is not something you can really go by. I believe it is an altitude correction factor that changes it.

Yes, this is very true. Never trust the reported weather values for anything but knowing if you need a raincoat or not. Always use a weather metering device (like bracket racers use), as the reported baro reading is corrected to sea level conditions ... for the same reason dyno readings are corrected. I speak from experience.

[Blades]

Yeah, dammit.. That was in the back of my mind, but I couldn't put my finger on it. Where can I get an accurate baro sensor; not for the car, but to just.. check out the baro press.

[WS6FirebirdTA00]

accuracy=$$ lol

[EC_Tune]

Oregon Scientific or a good old fashioned mercury barometer (it's 40" tall at least!).

[12secSS]

Doug,
I can see you driving down the road with one of those 40" barometers sticking out of a 'vette.