This information is no where to be found on this forum simplified like this, so im posting it up. It is however on the forum, but it is written in a very technical detailed way so its harder for the average person to figure the system out without help from somebody else.

Heres the spoon fed version........... Enjoy.


EXAMPLE OF PSI BASED BOOST CONTROL SIMPLIFIED.:

Lets say you live at 14.7psiA and you want to run 30psi.. but the Boost Desired Engine 'PSI' table only goes to 30.1.. what do you do? you set the boost adder to 25, so that gives you an additional 10.3psi over your max limit of the Boost Desired Engine 'PSI' table for your 14.7psiA atmospheric pressure (0ft sea level)..

Next you set the Boost Desired Engine 'PSI' table to 19.7psi. Now you're covered for overboost up to your 30psi with still room to breath in the Boost Desired Engine 'PSI' table.

why? Because 14.7psia represents 0psi and adding 10.3psi onto that gives you 10.3psi with the boost adder ontop of your initial sea level absolute atmospheric pressure.

Example:
10.3psi + 19.7psi = 30PSI.

In short: Boost Adder (Plus) Boost Desired Engine 'PSI' Table (Minus) Your atmospheric pressure = your target boost

Now understand this doesn't represent the actual boost itself. you must set the main map wastegate duty cycle and zero out the Boost Error Correction (PSI)
and set a boost curve first, and then adjust the Boost Error Correction (PSI) to your needs. Never take to much wgdc % out for low psi corrections on the BEC table.

Also, don't forget to set your rom up for PSI based boost, by default, most of the v7 roms are setup for Load based boost error correction and control.
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THANKS GOES TO ROADSPIKE FOR DRILLING THIS INTO MY HEAD AND FINALLY MAKING ME UNDERSTAND HOW IT ALL WORKS ABOUT 3 MONTHS AGO.

 

Thank you. Im assuming its recommended to have a little headroom in the Boost Desired PSI table. Your example gives 5 psi headroom. Is that because the error correction wont add wgdc if the Boost Desired PSI table is maxxed out?

So if I were targeting 25 psi and live at sea level, then 14.7 in the Boost Adder table and 25 in the Boost Desired PSI table would be sufficient. Correct?

Got a 3 port to hook up and just wanting to make double sure I understand it all, as Ive never messed with ECU controlled boost.

 

Shouldnt that be absolute pressure? Whereas your example would be Boost Adder (14.7+10.3=25) + Boost Desired Engine 'PSI' (19.7) = Absolute Pressure (44.7psiA, 30psi on the gauge)?

Not criticizing, its just that the devil is in the details sometimes....

 

this is correct yes.

 

I can always edit it. I was gonna just rename it to "boost target" also, but then i didnt.

how it works is, if you live at sea level 14.7, the boost adder at 14.7 represents 0psi. so whatever you add over your sea level, counts as actual boost pressure + the boost desired engine psi table values. you understand it now?

Its easy to grasp once its explained in laymen terms, But as you can see it gets alittle tricky once you have to actually run more boost then the tables actually provide data up to.

 

I just posted about that descrepancy in case anyone else was to go 100% off of your "In short" description, then wonder why their boost was 14.7 psi lower than it should be.

I definitely understand the target and error correction tables now. Kindof what I had figured already. But had never thought about leaving headroom in Boost Desired Engine 'PSI' table. Im sure the BWGDC table is gonna be a shot in the dark. But I'll get it figured out.

 

Ya it just gets funky when you have to add more onto the boost adder. Its a bit confusing at first for sure!
Most cars I get always have the BEC zero'ed out because the previous tuner doesn't understand how it works.

 

That is actually incorrect. Your first paragraph is correct but this "in short" part is not. You are missing one important part.

It is:

Boost Adder + Boost Desired Engine 'PSI' Table - Your atmospheric (baro) = your target boost.

So if you live at sea level and you want to target 26psi @4,000rpm you can put:

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Boost Adder (14.7) + Boost Engine 'PSI' Table @ 4,000 rpm (26psi) = 40.7

40.7 - Your Atmospheric (baro) is 14.7 (if at sea level) = 26psi

So:

14.7 + 26 = 40.7 - 14.7 = 26

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It's easy with just setting the Boost Adder at your local atmospheric (Baro), The" tricky" part is if you want big boy boost and your Boost Engine 'PSI' Table maxes out at certain ceiling, but if you just do that simple equation I noted above all is good:

Boost Adder + Boost Desired Engine 'PSI' Table - Your atmospheric (baro) = your target boost.

 

Given the information above about the boost adder and sea level, they should understand the "in short" reference below. Again this was to be a simple example how it works without any technical jargon.

 

But it's not correct.

You put:

Which is not the correct equation, you are missing the atmospheric part. The correct equation is:

No technical jargon, one single equation, without the missing piece.

 

Ya i see it, ill fix it now.. I see what you're saying. Thanks for pointing that out. I looked at your - in your sentence and didnt realize it stood
for minus, because most people use - to separate words. You're right it wasnt jargon, i just misread it.

Its fixed.

 

Here is a pretty picture to make it even more simple:

 

yes even better. i will quote you posting that picture and put it in the first post. thanks

 

lol..thats what I was sayin

 

My boost desired table won't go above 24.6. Any help on that would be appreciated.

Thanks