Help me understand the dynamic air flow tab regarding the rpm enable and re enable

[Allen Vos]

I am struggling a little bit trying to understand the dynamic airflow tab underneath AIRFLOW/DYNAMIC in VCM editor.

I am working with an E38 Gen 4 LS3 in an 09 Vette.

I understand the dynamic air flow tabs, mainly High RPM Disable and High RPM Re-enable and their respective values are what dictate when the MAF is used and when its not.

My vehicle is 100% stock and I mainly got into HP tuners to remap my throttle body and fix a Lean stumble on cold start, but now would like to explore a bit of tuning and maybe tweak a few thing here and there.


So the "HIGH RPM DISABLE" tab is at 4000 RPM on my tune. The description for this tab says "Above this RPM use filtered MAF for airmass for air mass prediction calculation".

For the "HIGH RPM RE-ENABLE" tab is at 3900 RPM on my tune. The description for this tab says "If enable RPM must drop below this to enable airmass prediction calculations".


This is where it gets a touch confusing for me and I want to fully understand this before I dive into tuning.

On the "HIGH RPM DISABLE", mine being at 4000 rpm, what I'm getting from everything I've read, is that my E38 in stock form is using the MAF sensor below 4000rpm as well along with the VVE table for Airflow measurements. When the car goes over 4000 rpm its reading MAF and disregards the VVE table?


What I am really trying to understand is the "HIGH RPM RE-ENABLE" value. its 3900 RPM on my vehicle. So what exactly does this parameter mean or do? I know it says it must drop below this RPM to re-enable airmass prediction calculations.

Is "Airmass prediction calculation" another meaning for using the VVE table which relies on the MAP sensor for its values?

Does anyone have a proper definition of "Filtered MAF for airmass prediction calculations" and one for " airmass prediction calculations".

I'm just wondering why we need a Re-enable value when under 4000 rpm the stock tune uses VVE and MAF up to 4000RPM then MAF only after that?


Sorry its a bit confusing and I hope I don't sound like I am out in left field here, but I would like to fully understand these settings before tackling this.

Please correct any thing I've said if its not accurate.

Just trying to understand here

[Guy With A Chevy]

https://forum.hptuners.com/showthrea...ynamic-airflow

I think the idea is that unless the MAF is failed it is always using both but primarily one or the other. The engineers in that thread speak of many things, one to include how to tell exactly what state it is in.

https://www.google.com/search?q=hptu...f+rpm+settings

Also I just received Greg Banishes 2007 Engine Management Advanced Tuning book and I say it is a must for every tuner as a great start to learn tuning

[Allen Vos]

https://forum.hptuners.com/showthrea...ynamic-airflow

I think the idea is that unless the MAF is failed it is always using both but primarily one or the other. The engineers in that thread speak of many things, one to include how to tell exactly what state it is in.

https://www.google.com/search?q=hptu...f+rpm+settings

Also I just received Greg Banishes 2007 Engine Management Advanced Tuning book and I say it is a must for every tuner as a great start to learn tuning

Thank you for the response and the links, I did want to mention that I am not new to tuning, just new to HP Tuners and GM so for myself its not learning the basics of tuning but how HP Tuners goes about things.

Perhaps i did not explain myself well enough and got to detailed in my post.

I'm trying to focus on the HIGH RPM DISABLE and also the HIGH RPM RE-ENABLE settings and primarily looking for a thorough explanation on specifically what setting these will affect.

I have spent countless hours searching post and videos and have yet to see this explained thoroughly. Yes I know I can follow tutorials and plug in the appropriate numbers they tell me too, however, I really want to understand this function inside and out and why we set the numbers the way we do.



Ill try to explain this with a bit less detail than the original post.

This is what I've learned on the E38 Gen4.

In stock form the PCM uses MAF and VE(VVE) to figure out dynamic air flow to do its fuel/air calculations up to 4000 rpm which is what the HIGH RPM DISABLE is set too.

After 4000 rpm it uses the MAF only for fuel/air calculations.


I'm also aware that the MAF input is used at all times through the complete RPM range unless it is zeroed out or failed in VCM Editor so that the VE(VVE) table can be tuned.

I know that the HIGH RPM DISABLE value is the RPM set point that the PCM stops using the VE(VVE) table for fuel/air calculations.


Here is where I'm not understanding things 100%

The HIGH RPM RE-ENABLE function looks like it controls the PCM's ability to read the VE(VVE) and use it for fuel/air calculations?

I was hoping someone could chime in and explain this function with some detail.


I want to always tune MAF and VE(VVE) , but lets say hypothetically I wanted to use MAF through the whole rpm range but only use the VE(VVE) from say 2000RPM to 4000RPM, how would I set that up?

Also vice versa. What if I wanted to use the MAF starting at 2000RPM and up but use VE(VVE) from idle up to 4000 RPM?


Not trying to be a PITA here, just wanting to understand this a bit better, and hopefully this post will help out other people new to HP Tuners.

[smokeshow]

I want to always tune MAF and VE(VVE) , but lets say hypothetically I wanted to use MAF through the whole rpm range but only use the VE(VVE) from say 2000RPM to 4000RPM, how would I set that up?

Also vice versa. What if I wanted to use the MAF starting at 2000RPM and up but use VE(VVE) from idle up to 4000 RPM?


Not trying to be a PITA here, just wanting to understand this a bit better, and hopefully this post will help out other people new to HP Tuners.

You don't have the flexibility to pick and choose like that. The control authority of the speed density model and mass airflow measurement is overlapping for a reason - so they can check each other. There is also the added benefit of being able to bias the airflow estimation based on which airflow source happens to be more trustworthy. During torque transients, that is speed density; at high speed, that is MAF. And to your main question - dynamic airflow disabling at 4000rpm is partially due to the lack of need for what dynamic airflow offers in terms of accuracy at low RPM. But the overarching reason is CPU throughput. The hardware is not fast enough to manage all of the calculation required for dynamic airflow above 4000rpm on a V8 at its intended rate.

[RobZL1]

And to completely tie a bow on it, the "re-enable" is simply a hysteresis so the change point has some gap, like many other parameters in GM tunes.

[Allen Vos]

You don't have the flexibility to pick and choose like that. The control authority of the speed density model and mass airflow measurement is overlapping for a reason - so they can check each other. There is also the added benefit of being able to bias the airflow estimation based on which airflow source happens to be more trustworthy. During torque transients, that is speed density; at high speed, that is MAF. And to your main question - dynamic airflow disabling at 4000rpm is partially due to the lack of need for what dynamic airflow offers in terms of accuracy at low RPM. But the overarching reason is CPU throughput. The hardware is not fast enough to manage all of the calculation required for dynamic airflow above 4000rpm on a V8 at its intended rate.

Thank you for that explanation. I think what has been throwing me for a loop is all the hours I have spent reading about this and there being some bad information out there from peoplo who tune that shouldn't be.


One thing that had been confusing me is the High RPM RE-Enable tab description, "RPM must drop below to re-enable air mass prediction calculations."

Now I know this is for the VVE side of things using the MAP sensor. I had thought you could put it where ever you wanted and have say the MAF only work up to say 2000rpm and have
the VVE kick in at whatever RPM I specify.



Now, from what I understand on the E38, the MAF is on all the time regardless of any dynamic air flow setting which is why you must FAIL the MAF to disable?

Also is it good practice to keep the high rpm disable and reenable within 200-300RPM for that transition of air flow to go smoother?


For example a HIGH RPM DISABLE = 400 and a HIGH RPM RE-ENABLE = 300, would turn off dynamic air flow and run off the MAF only, disabling VVE\MAP (MAF tune only)

also if the HIGH RPM DISABLE = 8000 and a HIGH RPM RE-ENABLE =7900, with the MAF set to fail would be a VVE/MAP only tune.


I'm basically looking for clarification on my findings to make 100% sure I am not going down the wrong rabbit hole here, so everything you have said is greatly appreciated

[Allen Vos]

Thank you, so basically you want to be 200-300 rpm apart on the disable and re-enable no matter which way you tune it?

[RobZL1]

Thank you, so basically you want to be 200-300 rpm apart on the disable and re-enable no matter which way you tune it?

Bingo. You want to have some hysteresis or dead band there so it's not flipping back and forth as you approach and are around that RPM. Similar things in the rest of the tune, such as rev limits, PE, etc. It needs to fall below by a defined amount before it swaps back over to another strategy.

You are also correct on your notes about setting up the RPM points to achieve the modes you want (in addition to failing the MAF where appropriate).
All of that said, tuning VVE off of the MAF data is quicker. Probably makes sense to fail the MAF and tune VVE several times to get the feel for it, though, before you start tuning VVE off of the MAF. It will help with understanding of the VVE in general.

[Allen Vos]

Bingo. You want to have some hysteresis or dead band there so it's not flipping back and forth as you approach and are around that RPM. Similar things in the rest of the tune, such as rev limits, PE, etc. It needs to fall below by a defined amount before it swaps back over to another strategy.

You are also correct on your notes about setting up the RPM points to achieve the modes you want (in addition to failing the MAF where appropriate).
All of that said, tuning VVE off of the MAF data is quicker. Probably makes sense to fail the MAF and tune VVE several times to get the feel for it, though, before you start tuning VVE off of the MAF. It will help with understanding of the VVE in general.

Sweet!!! Thank you for clarifying all that for me. I know this will help me and hopefully others that search for a clear explanation on this topic.

I'm curious to know the way you tune? Did I read that correctly that you tune VVE from the MAF data?

Is this a more advanced way to do it? Everything I have come across so far has said that I would need to tune the MAF and VVE completely independent of each other, hence having to disable VVE for MAF tuning and disabling MAF for VVE tuning?

I know I'm off topic here but always looking for new and better ways to do things.

[RobZL1]

See the following for good background:

https://forum.hptuners.com/showthrea...ation-for-gen4

https://forum.hptuners.com/showthrea...-the-Same-Time

[SiriusC1024]

The way I think of it is "Above this RPM use filtered MAF for airmass (in place of) air mass prediction calculation." As stated by HPT's description "for" means the same thing, but it's ambiguous.

Airmass prediction calculations account for transients with high accuracy. This is due mostly to the comparison being drawn between MAF and MAP across the throttle body. (Details here: https://forum.hptuners.com/showthrea...ynamic-airflow). Thing is that's also computationally expensive. The thinking is that below 3900 rpm there is a lot of on-off-on pedal. That's where most normal driving occurs. Above 4000rpm it's usually a full power pull (acceleration) or holding (heavy towing), so airflow changes at a more or less linear rate. Again, due to compute resources, the compromise must be made to slim down calculations in order to keep engine control at the high resolution required to ensure safe power delivery.

Those enables could technically be set to run full-time. The problem in doing this is that at higher RPM's the synchronization of all calculations, fundamentally based on crank/cam triggers, will happen at a slower rate. Things that might need corrected or might need flagged could slip between loop updates, being addressed later than optimal.

Setting those values too low, disabling the airmass prediction, reduces accuracy.

So, air/fuel accuracy as much as possible and then transition to filtered MAF in order to maintain control as data and computation load increases.

[smokeshow]

Yeah, pretty much. Worth mentioning though is the obvious lack of blown up engines or other failure for those who set that disable value at 8000rpm or something really high on a V8. It would be problematic if it weren't for the RTOS task manager in the core application software that actively manages which functions are called at which rate. Once throughput limitation becomes an issue, the task manager slows things down preemptively to avoid a reset. You can quite literally watch the change happen in the relatively slow CAN data in the scanner, too. Once the task manager clamps down on function call frequency, the graph data starts to look jagged and messy. But it keeps the engine running

[SiriusC1024]

It's like framerate in a video game. You can play at 20fps, but it sucks. Framerate drops, so disable some of the post processing like ambient occlusion. Doesn't look as nice, but you can control the character better.

[Allen Vos]

See the following for good background:

https://forum.hptuners.com/showthrea...bration-f-gen4

https://forum.hptuners.com/showthrea...-the-Same-Time

Thank you so kindly for all of your help and the reading material.

[Allen Vos]

The way I think of it is "Above this RPM use filtered MAF for airmass (in place of) air mass prediction calculation." As stated by HPT's description "for" means the same thing, but it's ambiguous.

Airmass prediction calculations account for transients with high accuracy. This is due mostly to the comparison being drawn between MAF and MAP across the throttle body. (Details here: https://forum.hptuners.com/showthrea...ynamic-airflow). Thing is that's also computationally expensive. The thinking is that below 3900 rpm there is a lot of on-off-on pedal. That's where most normal driving occurs. Above 4000rpm it's usually a full power pull (acceleration) or holding (heavy towing), so airflow changes at a more or less linear rate. Again, due to compute resources, the compromise must be made to slim down calculations in order to keep engine control at the high resolution required to ensure safe power delivery.

Those enables could technically be set to run full-time. The problem in doing this is that at higher RPM's the synchronization of all calculations, fundamentally based on crank/cam triggers, will happen at a slower rate. Things that might need corrected or might need flagged could slip between loop updates, being addressed later than optimal.

Setting those values too low, disabling the airmass prediction, reduces accuracy.

So, air/fuel accuracy as much as possible and then transition to filtered MAF in order to maintain control as data and computation load increases.

Thank you for that explanation. For the next year or so I am going to be running the car in stock trim and learn to tweak things here and there. I am not sure if you have ever heard of a DIY engine computer called "Mega Squirt"? I had a mustang with a turbo setup on it and managed to tune that thing to run mid 9"s in the quarter. It was only a speed density system though with a single wideband and no error correction on the AFR so it was a pretty simple system.

This seems a lot more complex and much more to learn.

I plan on adding a fairly aggressive cam to the LS3 plus a good set of headers, exhaust and CAI.

I am concerned about tuning the low end idle and drivability and wondering how difficult it will be to tune with not much engine vacuum and some aggressive overlap on the cam?