Speed density tuning questions
01-27-2018, 04:29 PM
#41
Chopper Doc Internal engine dynamics is a very complicated subject due to the physics involved. Just think as that hot air is coming in, it has more pressure, meaning it's possible that it could put the MAP into another cell, while being less dense at the same time.
Another interesting point is as the IAT goes higher, the PCM will pull timing. Might not seem like a big issue at first, but with aftermarket cams and mods, timing has a bigger effect the actual vacuum the engine is pulling. Less timing, less vacuum which means slower air. As air velocity decreases, pressure increases. So wouldn't it be possible to get into another cell on your injector flow rate? Keep in mind, on that table, more vacuum equates to less fuel. As the MAP kpa goes up, (closer to baro = less vacuum) the flow rate is increased. This would have the greatest effect at idle.
I try and learn something new everyday. This is a neat topic and there is a ton to learn about it. I haven't even got into the effects of heat and compression, and it's already pretty complicated.
Another interesting point is as the IAT goes higher, the PCM will pull timing. Might not seem like a big issue at first, but with aftermarket cams and mods, timing has a bigger effect the actual vacuum the engine is pulling. Less timing, less vacuum which means slower air. As air velocity decreases, pressure increases. So wouldn't it be possible to get into another cell on your injector flow rate? Keep in mind, on that table, more vacuum equates to less fuel. As the MAP kpa goes up, (closer to baro = less vacuum) the flow rate is increased. This would have the greatest effect at idle.
I try and learn something new everyday. This is a neat topic and there is a ton to learn about it. I haven't even got into the effects of heat and compression, and it's already pretty complicated.
01-28-2018, 03:58 AM
#43
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When tuning VE, IAT can have a huge effect on your numbers. This is because there are no fueling tables that use IAT as a correction for fuel. I guess GM never intended on prolonged SD mode. The reason it happens is because the PCM uses the VE as the calculation for dynamic air, which is a hard number that does not change when you're driving around. This is also the number the PCM uses for calculating g/cyl. Whatever number is on the VE at a certain rpm is what it is. There is no adjustment for IAT.
When the MAF is enabled, though, then the PCM uses actual metered air to calculate g/cyl, and make fueling adjustments. On some PCMs the computer uses both to do this, like gen IVs where VE and MAF are biased based on RPM because VE is more accurate at lower RPM, whereas the opposite is true at higher RPM, so it biases MAF. The last gen IV I tuned I just disabled VE and tuned it for 100% MAF. This is a pretty common practice.
There is a silver lining though, while in SD you can still usually enable the STFT's so your O2's can help with making adjustments for fuel. The air calc still won't change though, and if it's off enough then the O2's will actually be more of a pain than a help.
So what it sounds like on your tune is VE was tuned at lower IAT temperatures. Fuel doesn't mix as well into hot air, and there is less air to mix with (hotter air is less dense, but has higher pressure because it's contained). Couple this with the increased chamber pressure due to heat equals more fuel is required to cool it down. GM accounts for this with ECT. The colder the engine, the more fuel. Also, the hotter the ECT, the more fuel. At operating temp, stoich is the target. Just have a look at a stock OL EQ table to see what I mean.
Moral of the story is heat has a huge effect on fuel, but GM assumes MAF will be used to calculate airmass. That is thier "correction" for heatsoak. What that means for us SD guys is try and tune the VE at temps that the car will most likely see, I.e. normal operating conditions. Either that, or account for it by tuning your idle cells when IAT is very high. This will cause the exact opposite of what you were seeing, as in a lean condition as soon as it starts cooling down, but creep back to stoich as it heats up.
I dealt with that for a while trying to find a happy medium. Without a WB it wouldn't be something you'd notice at all. But when you are a perfectionist, and you can see your afr all out of wack suddenly, even though the car runs great, you tend to look into more, and make unnecessary adjustments. A good friend of mine and I were discussing this recently because he has the exact same issue. We decided that perhaps a "winter tune" and "summer tune" might be the answer. I can say my summer VE table is definitely different than my current one.
When the MAF is enabled, though, then the PCM uses actual metered air to calculate g/cyl, and make fueling adjustments. On some PCMs the computer uses both to do this, like gen IVs where VE and MAF are biased based on RPM because VE is more accurate at lower RPM, whereas the opposite is true at higher RPM, so it biases MAF. The last gen IV I tuned I just disabled VE and tuned it for 100% MAF. This is a pretty common practice.
There is a silver lining though, while in SD you can still usually enable the STFT's so your O2's can help with making adjustments for fuel. The air calc still won't change though, and if it's off enough then the O2's will actually be more of a pain than a help.
So what it sounds like on your tune is VE was tuned at lower IAT temperatures. Fuel doesn't mix as well into hot air, and there is less air to mix with (hotter air is less dense, but has higher pressure because it's contained). Couple this with the increased chamber pressure due to heat equals more fuel is required to cool it down. GM accounts for this with ECT. The colder the engine, the more fuel. Also, the hotter the ECT, the more fuel. At operating temp, stoich is the target. Just have a look at a stock OL EQ table to see what I mean.
Moral of the story is heat has a huge effect on fuel, but GM assumes MAF will be used to calculate airmass. That is thier "correction" for heatsoak. What that means for us SD guys is try and tune the VE at temps that the car will most likely see, I.e. normal operating conditions. Either that, or account for it by tuning your idle cells when IAT is very high. This will cause the exact opposite of what you were seeing, as in a lean condition as soon as it starts cooling down, but creep back to stoich as it heats up.
I dealt with that for a while trying to find a happy medium. Without a WB it wouldn't be something you'd notice at all. But when you are a perfectionist, and you can see your afr all out of wack suddenly, even though the car runs great, you tend to look into more, and make unnecessary adjustments. A good friend of mine and I were discussing this recently because he has the exact same issue. We decided that perhaps a "winter tune" and "summer tune" might be the answer. I can say my summer VE table is definitely different than my current one.
In all other conditions I'm not seeing much over ambient on my IAT as I have a huge 1300 hp race intercooler. Maybe that will change when it's 20 degrees warmer, but it's not a problem for me to make any needed adjustments at that time.
What you aren't keeping in mind is also that I'm already past the limits of the maf with my only intention to keep adding more boost over time. With that in mind I went ahead and converted to SD immediately rather than try to scale everything to use a maf.
This car is a "toy" not a daily in fact I only put a little over 2000 miles on it in the year that I owned it. A lot of that was driving it home from out of state where I bought it. When it goes to the track it will be tuned for the conditions that day if any changes are needed.
I'm very happy with the way the car runs in SD open loop and it's my car so that's how I'm leaving it. The AFR has been consistent for me from 20 degree to 60 degrees temps with the exception of the rare case of very long idle periods without moving or the rare shut off then restart. Again, even then as soon as I'm moving everything returns to normal. Those short periods of 15 to low 16 AFR at idle are nothing to worry about. In fact many people actually tune their idle in the 15's on purpose.
01-28-2018, 04:15 AM
#44
TECH Fanatic
The only time I really see an issue with IAT now is after the car is warm shutting it off for a bit then on first start the IAT will be heat soaked causing a lean condition until I get moving again. Once moving it drops right back down and returns to stoich at idle/cruise. Going into the upper 15 to low 16 AFR at idle is nothing to be concerned about since it drops right back down once I get moving and is fine from then on. The only reason I even have that issue is because I would drive to get a log then pull in my garage and shut the car off while I looked over the log. I would then make any changes needed and start the car back up for another cruise to test. Upon first start it would be lean as the IAT was heat soaked. It would actually start dropping just backing the car out of the drive. By the time I get to the first stop sign at the end of my block it's already dropped and my AFR is back to normal. Nothing to worry about or worth tuning around in my opinion.
In all other conditions I'm not seeing much over ambient on my IAT as I have a huge 1300 hp race intercooler. Maybe that will change when it's 20 degrees warmer, but it's not a problem for me to make any needed adjustments at that time.
What you aren't keeping in mind is also that I'm already past the limits of the maf with my only intention to keep adding more boost over time. With that in mind I went ahead and converted to SD immediately rather than try to scale everything to use a maf.
This car is a "toy" not a daily in fact I only put a little over 2000 miles on it in the year that I owned it. A lot of that was driving it home from out of state where I bought it. When it goes to the track it will be tuned for the conditions that day if any changes are needed.
I'm very happy with the way the car runs in SD open loop and it's my car so that's how I'm leaving it. The AFR has been consistent for me from 20 degree to 60 degrees temps with the exception of the rare case of very long idle periods without moving or the rare shut off then restart. Again, even then as soon as I'm moving everything returns to normal. Those short periods of 15 to low 16 AFR at idle are nothing to worry about. In fact many people actually tune their idle in the 15's on purpose.
In all other conditions I'm not seeing much over ambient on my IAT as I have a huge 1300 hp race intercooler. Maybe that will change when it's 20 degrees warmer, but it's not a problem for me to make any needed adjustments at that time.
What you aren't keeping in mind is also that I'm already past the limits of the maf with my only intention to keep adding more boost over time. With that in mind I went ahead and converted to SD immediately rather than try to scale everything to use a maf.
This car is a "toy" not a daily in fact I only put a little over 2000 miles on it in the year that I owned it. A lot of that was driving it home from out of state where I bought it. When it goes to the track it will be tuned for the conditions that day if any changes are needed.
I'm very happy with the way the car runs in SD open loop and it's my car so that's how I'm leaving it. The AFR has been consistent for me from 20 degree to 60 degrees temps with the exception of the rare case of very long idle periods without moving or the rare shut off then restart. Again, even then as soon as I'm moving everything returns to normal. Those short periods of 15 to low 16 AFR at idle are nothing to worry about. In fact many people actually tune their idle in the 15's on purpose.
Another consideration is overlap, if you have any. This can actually cause a false lean condition because fresh air gets into the exhaust when both valves are open. This is only really noticeable at idle. Mine is very "lean" at idle, as in 20% or so, but I know it's fake because I have 20* of overlap at just .050". Any more than that makes it surge.
I'm not telling you to use the MAF. But a few others may have been thinking of that route and I have yet see anyone find the correction for IAT without a MAF. It's just one of those things you can just live with, like we do. My heatsoak gets particularly bad due to the trans cooler and oil cooler. I just wish there was a better place for the intake on f-bodies. That's why I do most of my idle logs with the hood up, IAT around 90. It ensures there is enough fuel later when it gets up to 170+ in traffic.
01-28-2018, 04:37 AM
#45
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There's nothing out of the ordinary with your idle AFR. I was just offering up an explanation as to what hearsoak does to an SD tune, since in the tune there is actually no correction for IAT. My car is in the same boat. I too am already over the MAF limit (512 g/s) without boost. It's not too hard really to get over that with big injectors.
Another consideration is overlap, if you have any. This can actually cause a false lean condition because fresh air gets into the exhaust when both valves are open. This is only really noticeable at idle. Mine is very "lean" at idle, as in 20% or so, but I know it's fake because I have 20* of overlap at just .050". Any more than that makes it surge.
I'm not telling you to use the MAF. But a few others may have been thinking of that route and I have yet see anyone find the correction for IAT without a MAF. It's just one of those things you can just live with, like we do. My heatsoak gets particularly bad due to the trans cooler and oil cooler. I just wish there was a better place for the intake on f-bodies. That's why I do most of my idle logs with the hood up, IAT around 90. It ensures there is enough fuel later when it gets up to 170+ in traffic.
Another consideration is overlap, if you have any. This can actually cause a false lean condition because fresh air gets into the exhaust when both valves are open. This is only really noticeable at idle. Mine is very "lean" at idle, as in 20% or so, but I know it's fake because I have 20* of overlap at just .050". Any more than that makes it surge.
I'm not telling you to use the MAF. But a few others may have been thinking of that route and I have yet see anyone find the correction for IAT without a MAF. It's just one of those things you can just live with, like we do. My heatsoak gets particularly bad due to the trans cooler and oil cooler. I just wish there was a better place for the intake on f-bodies. That's why I do most of my idle logs with the hood up, IAT around 90. It ensures there is enough fuel later when it gets up to 170+ in traffic.
01-28-2018, 07:57 AM
#46
TECH Fanatic
If I'm doing the calculation right my cam only has 4 degrees overlap. Intake and duration are both 228 on a 112 lsa. I'm aware of the widebands not necessarily being accurate at idle and I did originally have idle AFR at 15. I liked that, but decided to put it back to 14.7 for a little extra margin for heat soak. I also had a lean cruise setup around 15.2 but I was getting some tip in knock if I rolled into it from those conditions. I don't care about gas mileage much and didn't like the lack of response I got after pulling timing to eliminate the lean knock so I put more fuel in it and added the timing back. It's much more responsive in those areas now. At first it was a head scratcher because working on the tune and seeing different idle AFR all the time. After I figured out it was poor IAT sensor placement along with a slow to react sensor it all made sense. My problem was also escalated due to the tuning process of shutting the car down only long enough to check logs and adjust tune then restart.
Those sensors are tuned to about 6400 hz. So a lot of things can set them off. LS3 sensors seem particularly sensitive.
IAT doesn't have any real effect on the PCM for fuel, since there is no table for that. It just helps US monitor it and adjust fuel appropriately. In straight SD the PCM makes no adjustments to fuel at all, unless you're using fuel trims. IAT does affect spark though, so it does matter where the sensor is.
01-28-2018, 10:25 AM
#47
I'm guessing that is why the tuner on my car went SD cause the tuner before him was having trouble with the idle, he removed the MAF and SD tuned it, it does idle great unless it 30 degrees it want gas pedal for a few seconds, summer time it's all good. The engine does have surge a part throttle while driving, I've checked for intake leaks all seems good.
01-28-2018, 10:43 AM
#48
TECH Fanatic
I'm guessing that is why the tuner on my car went SD cause the tuner before him was having trouble with the idle, he removed the MAF and SD tuned it, it does idle great unless it 30 degrees it want gas pedal for a few seconds, summer time it's all good. The engine does have surge a part throttle while driving, I've checked for intake leaks all seems good.
If your afr is good on part throttle and it surges, try pulling some timing. That can calm down the bucking pretty easily. If you use the scanner you can do this while driving and find the right amount to pull. It doesn't take much.
01-28-2018, 10:56 AM
#49
TECH Fanatic
I'm guessing that is why the tuner on my car went SD cause the tuner before him was having trouble with the idle, he removed the MAF and SD tuned it, it does idle great unless it 30 degrees it want gas pedal for a few seconds, summer time it's all good. The engine does have surge a part throttle while driving, I've checked for intake leaks all seems good.
Getting the counts down will give the pcm enough control to help cold starts.
To tune the table you'll need to build a custom PID using: desired/dynamic*iac position. Then make a histo using values from 1-310 in at least 5 numeral increments. Less is better though. Should look like 1, 5, 10...310. You get the idea I hope. Plot IAC position, and you'll get correction numbers.
01-29-2018, 12:55 AM
#50
When tuning VE, IAT can have a huge effect on your numbers. This is because there are no fueling tables that use IAT as a correction for fuel. I guess GM never intended on prolonged SD mode. The reason it happens is because the PCM uses the VE as the calculation for dynamic air, which is a hard number that does not change when you're driving around. This is also the number the PCM uses for calculating g/cyl. Whatever number is on the VE at a certain rpm is what it is. There is no adjustment for IAT.
Have you looked as the code to see how the PCM implements SD? Or do you know someone who has?
Or is it just obvious from data-logging that IAT changes screw up AFR in the way you'd expect without compensation?
Or are you assuming that there is no IAT compensation based on the fact that no IAT compensation tables are show in the tuning software that you're using? It doesn't necessarily need a table because it's just an equation (PV=nRT) so the absence of tables wouldn't necessarily mean the compensation isn't in there.
01-29-2018, 03:51 AM
#51
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IAT definitely has a major effect on AFR in SD. When I had the slow acting IAT sensor located in the filter per the procharger instructions I was getting a hotter reading then what was actually entering the engine. If colder denser air is going into the engine than what it thinks then of course your AFR will be leaner. No science needed I've seen it happen. That is what lead to me changing the sensor as well as relocating it right before the throttle body. Huge improvement!
There is also the add vs iat table in power enrichment which is an EQ ratio modifier. I'm already wanting to add more boost and thinking about a meth kit. I think the IAT PE modifier table as well as pulling timing at higher IAT if setup correctly could be a safety net if a meth system fails.
There is also the add vs iat table in power enrichment which is an EQ ratio modifier. I'm already wanting to add more boost and thinking about a meth kit. I think the IAT PE modifier table as well as pulling timing at higher IAT if setup correctly could be a safety net if a meth system fails.
Last edited by BCNUL8R; 01-29-2018 at 03:59 AM.
01-29-2018, 09:13 AM
#52
TECH Fanatic
I'm curious about what led you to believe this. I'm not saying you're wrong - I just bought my first LS-powered car a week ago and I'm trying to learn all I can about how it works. And SD without IAT compensation sounds like a pretty major oversight on GM's part. I and a few other hobbyists added SD to some Subaru ECUs (they're MAF-only from the factory), and we put IAT compensations in there because is seemed dumb not to. So it seems weird that GM would leave that out, considering how useful and obvious it is.
Have you looked as the code to see how the PCM implements SD? Or do you know someone who has?
Or is it just obvious from data-logging that IAT changes screw up AFR in the way you'd expect without compensation?
Or are you assuming that there is no IAT compensation based on the fact that no IAT compensation tables are show in the tuning software that you're using? It doesn't necessarily need a table because it's just an equation (PV=nRT) so the absence of tables wouldn't necessarily mean the compensation isn't in there.
Have you looked as the code to see how the PCM implements SD? Or do you know someone who has?
Or is it just obvious from data-logging that IAT changes screw up AFR in the way you'd expect without compensation?
Or are you assuming that there is no IAT compensation based on the fact that no IAT compensation tables are show in the tuning software that you're using? It doesn't necessarily need a table because it's just an equation (PV=nRT) so the absence of tables wouldn't necessarily mean the compensation isn't in there.
And as for the sensor, a friend of mine is struggling with the same issue. We even put the sensor directly in the intake, like many do with a boosted setup since boost causes heat. He also struggles with the effects of heatsoak, and unsurprisingly his VE table has been very hard to nail down with the temperature swings. You just have to set the number where you want it, under certain conditions.
As far as reading code, no not yet. I would like to learn more about that later. I got to this understanding by watching the afr error changes as IAT changes, and as predicted, it gets rich when hot, and lean when cold. This also depends on at what temperature you tuned it to. If you set the VE at lower IAT temps, the you'll actually see more of a change.
Another thing is when I tune the IAC effective area, desired and dynamic can be dead nuts on one day, change that by 40 or 50 degrees and then it's out by up to 50%. So that also throws in a whole other problem, as the motor moves around to compensate, it's adding more or less air, too. Cracking the hood and tuning it at 100 on IAT seems to work best. It's still off at anything above or below that though. But atleast it averages out.
This is all keeping in mind the VE is the combination of all adders and subtractors because commanded means nothing in SD. That's how you tune the table in the first place. Error from commanded. You can command whatever you want and tune the VE to match it. Hence why you leave PE and BE enabled and turn off everything else.
Last edited by ChopperDoc; 01-29-2018 at 12:50 PM.
01-29-2018, 10:57 AM
#53
TECH Fanatic
It would be nice if a GM engineer could weigh in here, because you're right, the PCM could compensate with a simple formula, however I just don't see it happening in my logs, of my car or of others I've tuned. The only time IAT doesn't seem to have an effect on afr is tuning straight MAF. Just did a gen IV this way, and it was no problem. Gen IV's are different though, and have more tables to correct the VE, since they actually use both in CL, substantially more than what a gen III does since it's only really used for transitions. Gen IV's bias VE under 4K, and bias MAF above on a sliding scale.
Otherwise, from my experience, heatsoak just remains an issue for a SD only tune.
As far as oversights go, one glaring example on a gen III is the lack of an altitude correction on VE too. It's included on newer pcms IV and up. It's not irrational to think they never intended SD to be a permanent thing, on gen III's at least.
I'm going to play with some logs later and plot IPW and IAT, probably add a few filters and see what I can find on this. I'll also plot AFR and do some math to see if the pcm is actually accounting for the IAT. I'm I'm reasonably certain it's not making any adjustments, whereas it just gets it's fuel numbers from the VE.
I'm on my phone right now so I can't verify this, but iirc, gen IV's have an IAT sensor cal. I know there is one for the MAP. I've never messed with either of those because I deal mostly with gen III's.
Otherwise, from my experience, heatsoak just remains an issue for a SD only tune.
As far as oversights go, one glaring example on a gen III is the lack of an altitude correction on VE too. It's included on newer pcms IV and up. It's not irrational to think they never intended SD to be a permanent thing, on gen III's at least.
I'm going to play with some logs later and plot IPW and IAT, probably add a few filters and see what I can find on this. I'll also plot AFR and do some math to see if the pcm is actually accounting for the IAT. I'm I'm reasonably certain it's not making any adjustments, whereas it just gets it's fuel numbers from the VE.
I'm on my phone right now so I can't verify this, but iirc, gen IV's have an IAT sensor cal. I know there is one for the MAP. I've never messed with either of those because I deal mostly with gen III's.
Last edited by ChopperDoc; 01-29-2018 at 12:20 PM.
01-29-2018, 04:10 PM
#54
TECH Fanatic
Okay, I did some further research into this, and as it turns out, THERE IS A CORRECTION FOR IAT in the tune. It's actually under: Engine>Airflow>Cylinder Charge temperature. On this table, higher values will bias ECT, and lower values will bias IAT. This is plotted over an airflow model in lbs/hr. Any adjustments made here will obviously require adjustments to the VE. Time to redo my tune. I'll report back when I get back to doing that. Car is down for maintenance right now (upgrades). Pretty good to know.
And, even in SD mode, the computer will pull fuel based on temperature. My IPW test turned out to be making adjustments after all. At low temps, around 40*, IPW averaged about 3.7ms. It tapers off slowly as it goes up. At 150* the PW is 2.7ms. All at idle, no throttle, total SD mode. AFR was very out of whack, though, and varied throughout, getting pretty lean at 150*, over 20%. This was the basis of my theory as to why AFR and heat seemed like a lost cause, because that makes no sense.
That was something I've seen pretty often, heat and error. I just accepted my idle error before, as from my understanding and trying to make sense of that, it was based on ECT, since all the fueling tables applicable at idle use that. Turns out this time I am actually pretty excited to be wrong on that. The computer does use ECT mostly, but on a bias. At low airflow, in my current tune, it leans towards ECT. Later, as the flow goes up, it biases IAT. This also explains why everywhere else on my table looked great, except at idle.
This is definitely worth looking into gents. If you have mods, and are having trouble with really bad error on your idle afr, try tuning this table a little to bias your IAT. I will work on creating a way to tune it using ECT, IAT, and A/F to see if there is a way to adjust for it. So far, the IAT vs IPW actually works fairly well, and could be used to a certain extent for reference. If it's getting lean like mine was, then adding more bias to the IAT should bring it down, right?
And, even in SD mode, the computer will pull fuel based on temperature. My IPW test turned out to be making adjustments after all. At low temps, around 40*, IPW averaged about 3.7ms. It tapers off slowly as it goes up. At 150* the PW is 2.7ms. All at idle, no throttle, total SD mode. AFR was very out of whack, though, and varied throughout, getting pretty lean at 150*, over 20%. This was the basis of my theory as to why AFR and heat seemed like a lost cause, because that makes no sense.
That was something I've seen pretty often, heat and error. I just accepted my idle error before, as from my understanding and trying to make sense of that, it was based on ECT, since all the fueling tables applicable at idle use that. Turns out this time I am actually pretty excited to be wrong on that. The computer does use ECT mostly, but on a bias. At low airflow, in my current tune, it leans towards ECT. Later, as the flow goes up, it biases IAT. This also explains why everywhere else on my table looked great, except at idle.
This is definitely worth looking into gents. If you have mods, and are having trouble with really bad error on your idle afr, try tuning this table a little to bias your IAT. I will work on creating a way to tune it using ECT, IAT, and A/F to see if there is a way to adjust for it. So far, the IAT vs IPW actually works fairly well, and could be used to a certain extent for reference. If it's getting lean like mine was, then adding more bias to the IAT should bring it down, right?
Last edited by ChopperDoc; 01-29-2018 at 05:42 PM.
01-29-2018, 06:43 PM
#56
ChopperDoc is on point....
...charge temp blending can affect how much IATs will screw with AFR. Took me awhile to figure this out. I biased towards ECT since that is typically more stable once warm.
....MAFs are actually measured air compared to a theorhetical equation, but requires accurate fuel table values to be good. All my stuff is typically either hybrid or MAF only and they drive great.
....when you have a cam with positive overlap and longtubes headers running a hybrid closed loop is the way to go. Open loop at idle and when you read a set rpm turn on closed loop.
I will beg to differ on the mafs having such a low limit of being maxxed out. See sig for tutorial. 750-800whp can be done with a MAF, possibly more, but that's the limit of what I've tested.
...charge temp blending can affect how much IATs will screw with AFR. Took me awhile to figure this out. I biased towards ECT since that is typically more stable once warm.
....MAFs are actually measured air compared to a theorhetical equation, but requires accurate fuel table values to be good. All my stuff is typically either hybrid or MAF only and they drive great.
....when you have a cam with positive overlap and longtubes headers running a hybrid closed loop is the way to go. Open loop at idle and when you read a set rpm turn on closed loop.
I will beg to differ on the mafs having such a low limit of being maxxed out. See sig for tutorial. 750-800whp can be done with a MAF, possibly more, but that's the limit of what I've tested.
01-29-2018, 07:11 PM
#57
TECH Fanatic
ChopperDoc is on point....
...charge temp blending can affect how much IATs will screw with AFR. Took me awhile to figure this out. I biased towards ECT since that is typically more stable once warm.
....MAFs are actually measured air compared to a theorhetical equation, but requires accurate fuel table values to be good. All my stuff is typically either hybrid or MAF only and they drive great.
....when you have a cam with positive overlap and longtubes headers running a hybrid closed loop is the way to go. Open loop at idle and when you read a set rpm turn on closed loop.
I will beg to differ on the mafs having such a low limit of being maxxed out. See sig for tutorial. 750-800whp can be done with a MAF, possibly more, but that's the limit of what I've tested.
...charge temp blending can affect how much IATs will screw with AFR. Took me awhile to figure this out. I biased towards ECT since that is typically more stable once warm.
....MAFs are actually measured air compared to a theorhetical equation, but requires accurate fuel table values to be good. All my stuff is typically either hybrid or MAF only and they drive great.
....when you have a cam with positive overlap and longtubes headers running a hybrid closed loop is the way to go. Open loop at idle and when you read a set rpm turn on closed loop.
I will beg to differ on the mafs having such a low limit of being maxxed out. See sig for tutorial. 750-800whp can be done with a MAF, possibly more, but that's the limit of what I've tested.
Basically if it's hot and lean> bias ECT more
If it's hot and rich> bias IAT more
I know there is no particular horsepower limit for MAF, only the hard coded 512 g/s (gen III), which is easily scaled down. I'm not about to explain how to do that on here though. At least not today.
I agree, MAF is the way to go, especially for street use. I have one in my car, but haven't had a chance to get back to using it. I will though, which is why it's still there.
Last edited by ChopperDoc; 01-29-2018 at 07:29 PM.
01-29-2018, 07:31 PM
#58
Thanks. You are correct for biasing towards ECT. For everyone reading this; It works in opposite directions. If you bias IAT, and the computer over correcst, it gets lean when it's hot. If it's getting rich, go the other way and bias it towards IAT.
I know there is no particular horsepower limit for MAF, only the hard coded 512 g/s (gen III), which is easily scaled down. I'm not about to explain how to do that on here though. At least not today.
I agree, MAF is the way to go, especially for street use. I have one in my car, but haven't had a chance to get back to using it. I will though, which is why it's still there.
I know there is no particular horsepower limit for MAF, only the hard coded 512 g/s (gen III), which is easily scaled down. I'm not about to explain how to do that on here though. At least not today.
I agree, MAF is the way to go, especially for street use. I have one in my car, but haven't had a chance to get back to using it. I will though, which is why it's still there.
01-29-2018, 08:03 PM
#59
TECH Fanatic
You don't have to explain scaling the maf....it's already in my sticky lol. Unfortunately the other parameter that will limit the maf is the frequency. At some point you will hit the ceiling on the maf frequency for a given maf in a given tube diameter. I was making about 700fwhp when I hit the 12khz ceiling on a stock MAF, moving to an ls7 MAF in a 4 inch tube will drop the frequency which increases the range.
01-30-2018, 01:26 AM
#60
Cool, I'm glad to know that the GM engineers didn't just forget that temperature affects density. 
It makes sense to use an ECT compensation at low airflow since the block & heads will heat the intake charge a little bit when the air is moving very slowly. I never thought of that before. Subarus generally run closed-loop at low airflow, so the ECU just deals with it automagically.
Ironically, there are a bunch of Subarus out there with GM IAT sensors in the intake manifolds. (Including mine.) The factory system has the MAF/IAT unit right behind the air filter presumably just because the MAF sensor works better there and it needs to know IAT to work properly... but of course with SD fueling you really want the temperature in the manifold, and GM sensors play nice with Subaru's IAT input.
Where is the IAT sensor on the factory Gen III setups? Does it vary by car?
It makes sense to use an ECT compensation at low airflow since the block & heads will heat the intake charge a little bit when the air is moving very slowly. I never thought of that before. Subarus generally run closed-loop at low airflow, so the ECU just deals with it automagically.
Ironically, there are a bunch of Subarus out there with GM IAT sensors in the intake manifolds. (Including mine.) The factory system has the MAF/IAT unit right behind the air filter presumably just because the MAF sensor works better there and it needs to know IAT to work properly... but of course with SD fueling you really want the temperature in the manifold, and GM sensors play nice with Subaru's IAT input.
Where is the IAT sensor on the factory Gen III setups? Does it vary by car?