pgmfi.org

I am looking at the crome maps and such and i understand just about all except mbar. i know its what the map sensor is sensing( i think anyway) but i dont understand more than that can someone give me a quick run down on how it relates in tuning?

mbar is a metric standard, like in/hg or psi. it is in absolute as opposed to negative/positive

so if i am understanding correctly...
if my car is at 8 PSI its at what mbar? or is mbar only for vacume?

millibar is 1 thousanth of a bar, so 1000millibar = 1.0 bar

8 psi BOOST is 1 bar + 8psi, there is 14.5 psi in 1 bar therefore 8 psi is arond 1.55 bar of manifold pressure (absolute pressure) OR 1550 millibar.

wait.. 8psi is 1 bar? or 14.5 psi is 1 bar?

1 bar = 14.5 psi (use google, it does unit conversion as well as link to sites that do it too).

http://www.google.com/search?client=safari&rls=en&q=1+bar+to+psi&ie=UTF-8&oe=UTF-8

He is converting his units man...... You can't add 1 pound and 1 killo....
1bar + 8psi = ?
here's how it goes:
we first convert bar -> psi: 1bar = 14.5 psi, so the above becomes:
14.5psi + 8psi = ? well, it's = 22.5psi
Now, we'll go back to bars: 22.5psi / 14.5 = 1.55bar
and to millibars: 1.55bar * 1000 = 1550mbar

thanks man.. so now i have that part... so how does that pertain to tuning ? in crome the left side is mbar and the top is fuel . trying to learn how it works.

In CROME the columns show the vacuum, and the rows show RPM.
So, if you are at idle, the engine is at low RPM, and since the throttle is closed, there is high vacuum. High vacuum = small mBar reading, so the ECU will be using the values from the upper ( low rpm), left-hand ( small mBar) portion of the maps.

At WOT, just before you hit the rev-limiter, there's high RPM and low vacuum because the throttle is open, so this time, the ECU will be using values from the lower ( high RPM), right-hand ( high mBar and low vacuum) part of the table.

If you were in this WOT situation and totally released the gas pedal, the revs would start rapidly falling. Right after you release the pedal, the ECU will see high revs and will stay in the bottom rows, but since you've closed the throttle, the vacuum wil become high, and the ECU will move to the left columns. So the ECU will be using value from the lower, left-hand side of the maps. And as you slow down with the gas released, the ECU will be staying in the left part of the map and slownly moving from bottom to top, as revs are decreasing.

Very clear and beautiful explication, I guess this need to be wiki-ed

Agreed!!!!!!!!!!!!!! TY awsome explanation

wow, you're right, that was very well put!