Total Airflow PID

[AlmightyFork]

Hello,

I have an NSRT4. I've noticed that if I change the throttle body airflow map that it appears to correlate with the Total Airflow pid. Anyone have any insight on how this pid is used? I was hoping to raise my low throttle voltage airflow levels to reduce my idle VE numbers, but I'm not sure it works that way. Does this have any effect on commanded torque? Any ideas how commanded torque might be calculated? I know I have my desired torque table, but it bugs me seeing numbers higher than my vehicle likely makes.

[AlmightyFork]

Maybe I'm looking at airflow all wrong. I've heard that larger turbos flow more at the same psi, but I'm starting to question this. The ideal gas law argues against this. Maybe a larger turbo at the same psi just increases ve?

I still can't figure out how commanded torque interacts with the airflow/wgdc model.

[PurpleRam]

Hello,

I have an NSRT4. I've noticed that if I change the throttle body airflow map that it appears to correlate with the Total Airflow pid. Anyone have any insight on how this pid is used? I was hoping to raise my low throttle voltage airflow levels to reduce my idle VE numbers, but I'm not sure it works that way. Does this have any effect on commanded torque? Any ideas how commanded torque might be calculated? I know I have my desired torque table, but it bugs me seeing numbers higher than my vehicle likely makes.

Our PCMs operate on the idea that Airflow=Torque , X amount of Total Air flow = X amount of torque ,….. simple way to look at this is , you hit the pedal , the pedal position tells the PCM I’m requesting X amount of TQ , the PCM responds with opening the Throttle body and adjusting Fuel based on desired AFR .
Now we can tell the PCM that we want, but doesn’t mean we get it , for example we set the table @ 110G/s at .78v…. and let’s say 110G/s = 320ftlbs@ 2500rpms , if TQ from engine is more(ie 320ftlbs) than what the pedal request is asking for (ie 300ftlbs )the PCM will close the Throttle body to match airflow to current level needed , so the TB would then flow 100G/s @ .78v instead of the 110 we are wanting it to flow…….again this is just a simple way to look at it, there are a lot more things going on here , but the same is true if it was opposite , say the Pedal request is for full 100% power(ie 520ftlbs) at .78v and the engine needs 375G/s to hit that Tq level, the old value at .78v might be 100G/s=300ftlbs , the new value will let the engine make 320ftlbs @ .78v because we set that value to 110G/s
There’s real good thread on here , I think it was “Tuning for Bigger Throttle Body” it’s a few years old circa 2019/2020 , search for it , it’ll answer some questions for you.

[Stoopalini]

I've always thought of the Throttle Body Airflow Model table (along with the large and small range tables) as characteristic tables for the airflow through the throttle body and intake tract ... rather than a demand table. It is not the same "Airflow Model" being referenced when talking about ANN or VE, etc ...

I believe the total airflow PID is just reporting the TB airflow value from the table itself.

Here is the thread PurpleRam is referencing, and it is worth the read. HemiTuna does a great job explaining some of the detail on how it works.

https://forum.hptuners.com/showthrea...+throttle+body

[PurpleRam]

I've always thought of the Throttle Body Airflow Model table (along with the large and small range tables) as characteristic tables for the airflow through the throttle body and intake tract ... rather than a demand table. It is not the same "Airflow Model" being referenced when talking about ANN or VE, etc ...

I believe the total airflow PID is just reporting the TB airflow value from the table itself. YES that's correct

Here is the thread PurpleRam is referencing, and it is worth the read. HemiTuna does a great job explaining some of the detail on how it works.

https://forum.hptuners.com/showthrea...+throttle+body

Yeah beat me to it, I just found it again...LOL''''

(https://forum.hptuners.com/showthrea...-Throttle-Body )


those tables are more of ....and it's hard to explain , it's not a request as much as it's an "allowance" , because the Throttle body will only flow so much air at WOT , and the small range table has a hard limit( at least in the NGC series, been a while since I played with any of the GPEC stuff) when you log TAF , 90% of the time it looks like a saw blade, that's because the TB is always adjusting .

[Stoopalini]

Yeah beat me to it, I just found it again...LOL''''

(https://forum.hptuners.com/showthrea...-Throttle-Body )


those tables are more of ....and it's hard to explain , it's not a request as much as it's an "allowance" , because the Throttle body will only flow so much air at WOT , and the small range table has a hard limit( at least in the NGC series, been a while since I played with any of the GPEC stuff) when you log TAF , 90% of the time it looks like a saw blade, that's because the TB is always adjusting .

Yeah, I believe (could be wrong though?) it's theoretical airflow volume through the throttle body at the speed of sound, when the throttle blade is open as wide as the voltage applied would result.

Here's how my table is currently setup for my Whipple charged 5.7, which has a 92mm Hellcat throttle body on it:

TB_Airflow_Current.JPG

So if the torque request being made requires say 289.33 g/s airflow, and the PCM determines the air flow speed is at the speed of sound .... then the PCM would hit the TB with 1.5v. If the PCM determines the air flow speed is less than the speed of sound, it would hit the TB with more then 1.5v to open it wider, so the same volume would be ingested, etc ...

I also *think* the "Min Phi" correction table may provide one of the variable inputs into how the PCM determines what the airflow speed is .... again, could be wrong here though, as I'm still learning all of this.

[PurpleRam]

Yeah, I believe (could be wrong though?) it's theoretical airflow volume through the throttle body at the speed of sound, when the throttle blade is open as wide as the voltage applied would result.

Here's how my table is currently setup for my Whipple charged 5.7, which has a 92mm Hellcat throttle body on it:

TB_Airflow_Current.JPG

So if the torque request being made requires say 289.33 g/s airflow, and the PCM determines the air flow speed is at the speed of sound .... then the PCM would hit the TB with 1.5v. If the PCM determines the air flow speed is less than the speed of sound, it would hit the TB with more then 1.5v to open it wider, so the same volume would be ingested, etc ...

I also *think* the "Min Phi" correction table may provide one of the variable inputs into how the PCM determines what the airflow speed is .... again, could be wrong here though, as I'm still learning all of this.

I would take the Speed of sound out of the equation(I could be wrong) keep in mind that Pedal request and pedal power% and to an extent Trans Tq tables play a role in this also. on NA vehicles I've found that Vacuum also plays in to it.

Have you read through this thread yet ? it's a good read .... for anyone else reading this, Search out and read a lot of HemiTuna's posts along with 6.1SRT300 ( I think that was his username) HassEXP those guys really did some of the good early hemi(and a lot crosses over to the 4&6 cyl tunes) trail and error stuff.
my experience has been Phi table reacts differently for the boosted crowd then it does for the NA crowd(which favors the speed of sound thinking)
https://forum.hptuners.com/showthrea...th-a-S-C/page2

The 85mm TB on the 5.7/6.1 Hemi engine will top out around 550 G/sec , but the OEM table at 3.79v is over 1000g/sec, they'll never flow those kinds of #s NA or boosted , but we have the option to set that main table to 1053(ish) @ 3.79v on my stocker Rumble bee I have that set at 600 from 2.5 v to 3.80v but real world it's never gone over 375.
The 448 in my not so stocker Rumble bee , has Phi set to 0 , I also have a 148mm TB(old Kenne Bell DBW for Dodge) and a sheet metal top on that Hi-Ram. that'll pass 890G/s at WOT and is set 1000 from 2.25 to 2.75, I rescaled it to max out at 2.75V ( it is a drag truck , I don't need much drivability), now real world it' topped out 748G/s

If you google G/s = HP '
you?ll come up with a some interesting results, but basically it boils down to 1.05 to 1.10 X G/S = close approx of RWHP.
FWIW my 448 bee's best MPH was at 748G/s which matched Wallace 1/4 calc est of 785 Hp based on wt of the truck.

so back to OP org question, no this table won't lean out your VE , because the PCM adjusts Fuel based on AFR and not airflow ...I know, I know , what all of you are thinking, but it's airflow = speed, AFR = Volume ,(ok again it's looking like I'm wrong on the speed of sound thing)

[Stoopalini]

I would take the Speed of sound out of the equation(I could be wrong) keep in mind that Pedal request and pedal power% and to an extent Trans Tq tables play a role in this also. on NA vehicles I've found that Vacuum also plays in to it.

Have you read through this thread yet ? it's a good read .... for anyone else reading this, Search out and read a lot of HemiTuna's posts along with 6.1SRT300 ( I think that was his username) HassEXP those guys really did some of the good early hemi(and a lot crosses over to the 4&6 cyl tunes) trail and error stuff.
my experience has been Phi table reacts differently for the boosted crowd then it does for the NA crowd(which favors the speed of sound thinking)
https://forum.hptuners.com/showthrea...th-a-S-C/page2

The 85mm TB on the 5.7/6.1 Hemi engine will top out around 550 G/sec , but the OEM table at 3.79v is over 1000g/sec, they'll never flow those kinds of #s NA or boosted , but we have the option to set that main table to 1053(ish) @ 3.79v on my stocker Rumble bee I have that set at 600 from 2.5 v to 3.80v but real world it's never gone over 375.
The 448 in my not so stocker Rumble bee , has Phi set to 0 , I also have a 148mm TB(old Kenne Bell DBW for Dodge) and a sheet metal top on that Hi-Ram. that'll pass 890G/s at WOT and is set 1000 from 2.25 to 2.75, I rescaled it to max out at 2.75V ( it is a drag truck , I don't need much drivability), now real world it' topped out 748G/s

If you google G/s = HP '
you?ll come up with a some interesting results, but basically it boils down to 1.05 to 1.10 X G/S = close approx of RWHP.
FWIW my 448 bee's best MPH was at 748G/s which matched Wallace 1/4 calc est of 785 Hp based on wt of the truck.

so back to OP org question, no this table won't lean out your VE , because the PCM adjusts Fuel based on AFR and not airflow ...I know, I know , what all of you are thinking, but it's airflow = speed, AFR = Volume ,(ok again it's looking like I'm wrong on the speed of sound thing)

Ha! Exactly .... talking through this in real time can often create a circular feedback loop of ideas :P

The reason I mention speed of sound, and it being a characterization table, is because I think it would explain why the OEM numbers are so high. At WOT, the velocity wouldn't be at the speed of sound, so actual air flow volume would be much less than what is populated in the table.

There's also air density to consider too. That 550G/sec maximum must be assuming a particular density of air, right? Change the density through temperature or pressure (ie: forced induction or baro changes) and that would impact the max G/sec I'd think?

This would mean the theoretical airflow maximum would need to assume a default pressure (1.0 bar maybe?) as well as a default temperature (no idea on what would be reasonable for that) and finally a fixed velocity (speed of sound?) .... Again, all conjecture here on my part though.

Have you read through this thread yet ? it's a good read .... for anyone else reading this, Search out and read a lot of HemiTuna's posts along with 6.1SRT300 ( I think that was his username) HassEXP those guys really did some of the good early hemi(and a lot crosses over to the 4&6 cyl tunes) trail and error stuff.
my experience has been Phi table reacts differently for the boosted crowd then it does for the NA crowd(which favors the speed of sound thinking)
https://forum.hptuners.com/showthrea...th-a-S-C/page2

Yeah, I've read (and re-read) that thread a few times now. HassEXP is definitely a great guy to bounce ideas off of when trying to get to the underlying functionality behind this stuff.

[AlmightyFork]

Our PCMs operate on the idea that Airflow=Torque , X amount of Total Air flow = X amount of torque ,….. simple way to look at this is , you hit the pedal , the pedal position tells the PCM I’m requesting X amount of TQ , the PCM responds with opening the Throttle body and adjusting Fuel based on desired AFR .
Now we can tell the PCM that we want, but doesn’t mean we get it , for example we set the table @ 110G/s at .78v…. and let’s say 110G/s = 320ftlbs@ 2500rpms , if TQ from engine is more(ie 320ftlbs) than what the pedal request is asking for (ie 300ftlbs )the PCM will close the Throttle body to match airflow to current level needed , so the TB would then flow 100G/s @ .78v instead of the 110 we are wanting it to flow…….again this is just a simple way to look at it, there are a lot more things going on here , but the same is true if it was opposite , say the Pedal request is for full 100% power(ie 520ftlbs) at .78v and the engine needs 375G/s to hit that Tq level, the old value at .78v might be 100G/s=300ftlbs , the new value will let the engine make 320ftlbs @ .78v because we set that value to 110G/s
There’s real good thread on here , I think it was “Tuning for Bigger Throttle Body” it’s a few years old circa 2019/2020 , search for it , it’ll answer some questions for you.

Thank you. I'm not using electronic throttle control though. I also do not see how commanded torque maps to airflow anywhere. Making changes to this table though still does alter driving characteristics.

[AlmightyFork]

Yeah, I believe (could be wrong though?) it's theoretical airflow volume through the throttle body at the speed of sound, when the throttle blade is open as wide as the voltage applied would result.

Here's how my table is currently setup for my Whipple charged 5.7, which has a 92mm Hellcat throttle body on it:

TB_Airflow_Current.JPG

So if the torque request being made requires say 289.33 g/s airflow, and the PCM determines the air flow speed is at the speed of sound .... then the PCM would hit the TB with 1.5v. If the PCM determines the air flow speed is less than the speed of sound, it would hit the TB with more then 1.5v to open it wider, so the same volume would be ingested, etc ...

I also *think* the "Min Phi" correction table may provide one of the variable inputs into how the PCM determines what the airflow speed is .... again, could be wrong here though, as I'm still learning all of this.

How might this be used without electronic throttle control?

[AlmightyFork]

so back to OP org question, no this table won't lean out your VE , because the PCM adjusts Fuel based on AFR and not airflow ...I know, I know , what all of you are thinking, but it's airflow = speed, AFR = Volume ,(ok again it's looking like I'm wrong on the speed of sound thing)

I know that it used o2 sensors to do trims. My thought however was kind of around these lines.

The SRT4 stock map has a pretty high VE around 1000 rpms and low map pressure. Much higher than I might have expected to see (~70%+ vs ~40%). I guess I thought I could crank up the modeled airflow in order to reduce my VE numbers (implying less total flow at that point as a percentage). I suppose it doesn't really matter if it's running good.

[AlmightyFork]

I still cannot seem to understand how we translate a commanded torque value to an airflow value for WGDC.

[HaasExp]

I guess I thought I could crank up the modeled airflow in order to reduce my VE numbers (implying less total flow at that point as a percentage). I suppose it doesn't really matter if it's running good.

The modeled airflow tables should not alter the VE or any fuel trims because these systems are still based on the SD model and the ideal gas law to estimate the actual airflow entering the cylinders.

I'm still not entirely sure what you are trying to achieve by wanting to lower your VE numbers (besides making it look closer to what you expect to see) but IF you wanted to do this, then you could REDUCE the injector fuel masses by say 10% for the same IPW's. Thus, the PCM would increase the IPWs by 10% to provide the required mass, which will theoretically result in 10% more fuel mass being injected for a given VE. Drop the VE by 10% and you should be back to where you started but with lower VE's.

I've heard that larger turbos flow more at the same psi, but I'm starting to question this. The ideal gas law argues against this.

The ideal gas law does not argue against this as P*V is proportional the amount or air molecules (n) eg PV ∝ n (R is a constant and for simplicity we can also consider T as a constant for the full equation PV = nRT).
So, a larger turbo pushing more air molecules at a given pressure ratio would have to result with increasing volume to maintain that equation.
However, in an engine, the volume is fixed by the displacement * VE. Thus a "larger" turbo would result in an increase in boost pressure on the same engine to maintain the equation.