Dual Baro sensors on Big stuff 3

[SPARKY]

I was crusing around looking at EFI systems.  I saw a second Baro option on a Big Stuff 3----where would you mount it---what would it do?

[Dean Los Angeles]

Where did you see that?

I looked through the manual and didn't see a reference.

[SPARKY]

I saw one on an eng on a dyno---I asked waht the extra Baro Sensor was coming out of the other end of the "BOX" and was told it was for atmospheric press.  I asked where one would mount it or the probe and they didnt know.  Seems to me that under way it would be easy to get a "non static" reading

[Dynoroom]

There are a couple of things you might want to do with a 2nd baro. Air box pressure, crankcase vacuum, pressure diff. thru chargeair cooler, are a few.

[SPARKY]

Ah so   more for data logging than for tune---thanks Mike sook forward to seeing you guys on the salt!!!!!!!1

[joea]

..............turbine inlet pressure......so as to
compare to boost pressure........see how the turbo
is workin.........

[dieselgeek]

My guess is that it's just like all the other EMS's have had for years - one baro sensor for realtime atmospheric changes, and another for manifold pressure.  Normally with a single MAP sensor, the system takes a pressure reading of atmospheric air immediately when it's powered on...  and bases it's Gas Law calculations off of that initial reading.  But...  say you are in a street car and you drive in a single trip up mount Baldy, 5000' then your EMS might have issues (depending on how it calculates required fuel)...  with a secondary, real time baro sensor making continuous samples, corrections can be made on he fly without resampling.

Usually, BS3 and similar systems assume you're running closed loop Exhaust Gas corrections to make up for this, but when running open loop mode, it's nice for that fancy EFI system to make the changes automatically without having to sample exhaust gases.

GM did a white paper on this years ago, there's more to it than just manifold pressure (some people ask why the second sensor is necessary if you have manifold absolute pressure data realtime); the change in exhaust backpressure with significant density altitude changes throws a speed density tune off, by a lot.



BS3 is one of the most poorly documented systems out there, IMO.  There are numerous hardware versions of it floating around and it's hard to tell what you are getting.

[Quick86GN]

I think what you were seeing was a 2nd map sensor(2 bar) on the Data logging External (DAE) option that is used for oil pan vac. This is important for dry sump & engines with vac. pumps and give us a heads up on ring seal and will help identify detonation.

Dale

[Greg Kelley]

Just to add a bit:

If you are blown or turbo the map sensor sees the cumulative pressure of  altitude + barometer + boost and the EFI uses that final number combined with RPM to determine fuel & spark.

In NA applications the map sensor sees altitude + barometer. If you are a bracket racer who might run at sea level one week and on the mountain the next week, you may be very happy to let the EFI make some adjustments. Some bracket racers (especially with alky fuel) don't want that adjustment and disable it in the software or unplug the map sensor.