Speed Density - Readings for Different Turbos

[mnetwork]

I have been scratching my head with this question all day. How does DSMLink work properly when using Speed Density or MAF Clamp at different boost levels. I understand it uses IAT and MAP plus engine speed to make corrections, but if you map out the VE table at 15psi and later raise boost to 25 and activate SD or MAFClamp how does the computer know how much fuel to supply? 25 psi on a 6262 and 25psi on a 16g are two very different things. How would the ECU know the difference? I can't seem to figure out how the ECU is going to compensate after dialing in VE at lower boost and raising boost.

 

[donniekak]

The speed density table you write on a 16g is going to have less VE than the larger turbo table.

 

[mnetwork]

I do understand this, but the airflow jump from 15psi to 25psi is also VERY different on a 16g and a 6262. If you calibrate the VE tables at lower boost the ECU knows what to do at higher boost?

 

[U8NTRDY]

I do understand this, but the airflow jump from 15psi to 25psi is also VERY different on a 16g and a 6262. If you calibrate the VE tables at lower boost the ECU knows what to do at higher boost?

Once you dial in the VE table, Its based on manifold pressure and IAT. More boost = More pressure, so the SD will adjust to compensate

This should help you out:
sd101 [ECMTuning - wiki]

 

[95g-s-x]

With SD, any changes you make to the intake or exhaust will change the ve. So if you are tuned for a evo 3 16g at 15 psi, and swap in a 6262 at 15psi, your tune WILL change. Even changing to a different air filter,intake tube,ic piping, ic, diferent 02 housing, or exhaust components can change your tune. It may be small, but it will change.

 

[mnetwork]

Once you dial in the VE table, Its based on manifold pressure and IAT. More boost = More pressure, so the SD will adjust to compensate

This should help you out:
sd101 [ECMTuning - wiki]

I get this, but let me ask this...

Is there ever a case where two turbos flow the same airflow at 15psi, but not at 30psi? If so, how would DSMLink know what to do with this?

 

[U8NTRDY]

I get this, but let me ask this...

Is there ever a case where two turbos flow the same airflow at 15psi, but not at 30psi? If so, how would DSMLink know what to do with this?

The best way I can put it is, (at least the is the way I understand it, someone please correct me if I'm wrong) but think of the SD as one big equation. In a mathematical equation, one side ALWAYS equates to the other. Now on one side of the equation you have all your variables, wich are all the parts and components of your setup. On the other side you have your tune. If one variable in the equation changes (i.e. boost pressure), everything must change to stay equivalent in accordance to the "ground rules" which would be the VE Table. The VE table is not the tune itself, Think of it as a reference point for the ECU wich keeps the tune in check.

So as for your example, If you have two turbos and one flows more air at 30psi than the other, although they are both producing 30lbs of boost at the turbo, this cannot be mixed up with your absolute manifold pressure wich should be higher with the turbo that flows more air and is what your ecu is using to calculate the air density (not boost pressure), which leads back to everything from before with the VE table and the tune.