AFR Stoich Gasoline E85 and Dash Gauge

[Speedy!]

Figured this was worth breaking out to a new thread for discussion. @jonx96 @Hpindy @16GoManGoHC2

The stoich point is programmable in the Hellcat. Factory is .0722. Divide it by 1 to get AFR of 13.85 that is close to what is displayed on the dash. Mine usually reads like 13.5ish on pump 93 at idle and cruise. PE is power enrichment and there's a separate table that is an adder for when WOT is achieved. That's how you get the WOT fueling where you want. Factory PE table is .0110 which is 12.02 AFR, but they rely on COT (catalytic converter over temp) which is yet another table with a fuel adder amount to come in pretty quick when the cats are calculated to be at a certain temperature (no actual sensor measuring temp) and you'll end up with a 10.5 or 10.8 or so AFR reading on the dash with pump gas when that happens.

To have the dash read the actual AFR on E85 the stoich point in the tune would need to be changed (with about a dozen other tables) to that of E85 as it has a different stoich point than gasoline. E85 is 9.85 (.1015). Straight gasoline stoich is 14.7 (.0683) and SRT chose 13.85 (.0722) for whatever reason. Most think that is to account for the ethanol in most pump gasoline these days. Locally mine says "up to 10% ethanol". Once you get in to flex fuel tuning, you actually have multiple stoich points in the tune to account for varying percentages of ethanol and that gets pretty complex with alcohol multipliers for PE as well as other things like cold start, etc.

Do you have to change the stoich point in the tune to make the dash read correctly, no. Is it the right way to do it? I think so as I believe that is how the factory would have done it if they put the car out to run on E85. Cars will run just fine without making that change though, as long as the injector data is setup properly for the fuel being used, like around 25-30% more on the fuel mass for E85. I prefer to know what tune and fuel are in the car and making this change allows me to take a quick look at the dash and know. If I see 9.8x at idle I know I'm on E85, 13.x I'm on gasoline. My flex fuel tune works the exact same way E40 is around low 11, E60 low 10, full E85 9.8.

All of that is talking AFR. If you're staying with a single fuel and know the stoich point and it never changes then dealing in AFR is fine. I did for YEARS on my old car. Once you start changing fuels with different stoich points it can get confusing so Lambda is a simpler way to think of it. Stoich for any fuel is Lambda 1. More than 1 is lean less than 1 is rich. HPTuners can read the wide bands in Lambda as well as some AFR settings for different fuels like gasoline, ethanol, LPG, etc, but you can't create a custom one like the Hellcat would need (13.85). Using Lambda is the easiest. For gasoline a Lambda of .82 - .83 is what I target for PE (WOT). .82 x 13.85 = 11.35 AFR. On E85 I target .81 Lambda at WOT .81 x 9.85 = 7.97. At WOT on my E85 tune my AFR gauge reads 7.97. Cruising around and idling Lambda will, or should, be very close to 1.

Clear as mud?

 

[BULL]

Subscribed

 

[Speedy!]

Here are a few screen shots from a 2020 Redeye factory tune file thanks to @DRAGRCR for sending it to me.

 

[Speedy!]

Finally, here's a stock Hellcat on the dyno. You can see where the Lambda starts off around .88 (12.1 AFR) and then suddenly drops to .75 Lambda (10.3 AFR) as cat over temp protection kicked in. That's a bit overkill on the fueling during COT in most tuner's opinions so that feature is usually disabled in a custom tune (mine included).

 

[16GoManGoHC2]

SWEET!! I’m going to have to study this!!!!

 

[Speedy!]

Make sure to have a cocktail ready lol. It can make your head spin. I've found quite a bit of simple math and some algebra used for these algorithms. Guess that's not surprising.

 

[Hpindy]

Make sure to have a cocktail ready lol. It can make your head spin. I've found quite a bit of simple math and some algebra used for these algorithms. Guess that's not surprising.

It will make your head spin when everything is going right ......... Throw a wrench in there say like a messed catch can system and watch out ! Lol

Sent from my BBF100-2 using Tapatalk

 

[Speedy!]

@Hpindy I'm curious how your catch can situation was impacting your tuning efforts. Dumping oil in the intake and messing up fuel trims or ?

 

[jonx96]

I have not built up the confidence to try out a tune yet. I'm still in the learning phase. I'm glad you have posted this. These are the type of posts I like to see. I have been waiting to get home to reply.
I've been trying to think what to type that you didn't cover above so for now I'm going to help break down somethings that helped me learn this part of the Hellcat tune.

The PE (Power Enrichment) table using either Aircharge vs RPM or PRatio vs RPM. Which is added by the stoich value. (Does anyone know why the Aircharge and Pratio are different?)
Breaking down stoich and power enrichment
.0722 Gasoline Stoich | .0110 =Aircharge vs RPM PE table
So
.0722+.0110=.0832
1.0/.0832=12.02
To find commanded you take 12.02/13.85=.87 Remember the 13.85 comes from 1.0/.0722=13.85


Next we have to dive into Volumetric Efficiency and Neural Network
From the research I have done it seems NN can mess with VE. Has anyone tuned with NN enabled? It seems like people have had good luck with it on a simple bolt on car. But tuning with VE seems like the way to go if I'm going to spend the time on VE anyway.
VE and NN both rely on Desired AFR. With that being said you can make it work not using the correct Stoich but it is more than just what shows on your dash that will be affected by not setting the correct stoich.

Some of this was a repeat of Speedy. I briefly read what he posted on my phone earlier and had a whole post planned out. Needless to say he has covered a lot more than I thought he did with Stoich. There was a lot of work that went into that post. This information should really help everyone understand. For me it helps looking at a stock tune and as I read what others post to look through the tune to help me learn.
I think this will be a very engaging thread and hope to share more once I wake up a bit after terrorizing mustangs all day.

 

[Speedy!]

Yep, you got it. One thing, you say to find "commanded" but what you're really showing is the Lambda value. It shows in HPTuners as commanded though, so I know what you're saying. If you're logging the right pids you can even see what the PE adder value is. The PID on my 2016 for that is "FA Enrichment".

The Hellcat isn't "supposed" to use VE. I put that in quotes because I have found a few random tables where apparently you can impact fueling with VE, but the tables are either mislabeled in HPTuners, or they do odd stuff I don't fully understand. I've mainly used these to correct areas where idle and cruise trims are different but use the same injector pulse width.

My 2016 has NN (neural network) enabled. This was introduced in the 2009 VVT motors to the best of my knowledge and tuners had fits with it back then. I had one of the first VVT motors that was supercharged and tuned and it was a challenge for the first year or two. AJ (Hemituner) tuned that car back then. If a car uses NN then supposedly it does not use VE (volumetric efficiency) but like I said, in some places it definitely does, just not for primary fueling at least on my Hellcat.

I don't know why aircharge and p-ratio have different values for power enrichment fueling. Maybe the table scaling is different enough to warrant that, but there is a drop down where you have to pick one or the other and Hellcats use aircharge. Because of that, I just copied my aircharge PE table values over to the p-ratio table, but it really wouldn't ever use them anyway.

 

[Hpindy]

@Hpindy I'm curious how your catch can situation was impacting your tuning efforts. Dumping oil in the intake and messing up fuel trims or ?

With the catch can clogged and not functioning properly crank case pressure was building up and forcing a small bit of oil in to the cylinders and screwing up the burn . It was very sporadic. Plus I was getting puffs of smoke during start up . Now that I cleaned everything and put the "flow in the proper orientation the tuning and trims are much more consistent .

Sent from my BBF100-2 using Tapatalk

 

[Hpindy]

I have not built up the confidence to try out a tune yet. I'm still in the learning phase. I'm glad you have posted this. These are the type of posts I like to see. I have been waiting to get home to reply.
I've been trying to think what to type that you didn't cover above so for now I'm going to help break down somethings that helped me learn this part of the Hellcat tune.

The PE (Power Enrichment) table using either Aircharge vs RPM or PRatio vs RPM. Which is added by the stoich value. (Does anyone know why the Aircharge and Pratio are different?)
Breaking down stoich and power enrichment
.0722 Gasoline Stoich | .0110 =Aircharge vs RPM PE table
So
.0722+.0110=.0832
1.0/.0832=12.02
To find commanded you take 12.02/13.85=.87 Remember the 13.85 comes from 1.0/.0722=13.85


Next we have to dive into Volumetric Efficiency and Neural Network
From the research I have done it seems NN can mess with VE. Has anyone tuned with NN enabled? It seems like people have had good luck with it on a simple bolt on car. But tuning with VE seems like the way to go if I'm going to spend the time on VE anyway.
VE and NN both rely on Desired AFR. With that being said you can make it work not using the correct Stoich but it is more than just what shows on your dash that will be affected by not setting the correct stoich.

Some of this was a repeat of Speedy. I briefly read what he posted on my phone earlier and had a whole post planned out. Needless to say he has covered a lot more than I thought he did with Stoich. There was a lot of work that went into that post. This information should really help everyone understand. For me it helps looking at a stock tune and as I read what others post to look through the tune to help me learn.
I think this will be a very engaging thread and hope to share more once I wake up a bit after terrorizing mustangs all day.

I was the same as you in the beginning. I was on the software doing compares and making "mock" tunes . I started off small and worked my way up . I did have some help all along the way . I'm still learning .

Sent from my BBF100-2 using Tapatalk

 

[zhc]

Yep, you got it. One thing, you say to find "commanded" but what you're really showing is the Lambda value. It shows in HPTuners as commanded though, so I know what you're saying. If you're logging the right pids you can even see what the PE adder value is. The PID on my 2016 for that is "FA Enrichment".

The Hellcat isn't "supposed" to use VE. I put that in quotes because I have found a few random tables where apparently you can impact fueling with VE, but the tables are either mislabeled in HPTuners, or they do odd stuff I don't fully understand. I've mainly used these to correct areas where idle and cruise trims are different but use the same injector pulse width.

My 2016 has NN (neural network) enabled. This was introduced in the 2009 VVT motors to the best of my knowledge and tuners had fits with it back then. I had one of the first VVT motors that was supercharged and tuned and it was a challenge for the first year or two. AJ (Hemituner) tuned that car back then. If a car uses NN then supposedly it does not use VE (volumetric efficiency) but like I said, in some places it definitely does, just not for primary fueling at least on my Hellcat.

I don't know why aircharge and p-ratio have different values for power enrichment fueling. Maybe the table scaling is different enough to warrant that, but there is a drop down where you have to pick one or the other and Hellcats use aircharge. Because of that, I just copied my aircharge PE table values over to the p-ratio table, but it really wouldn't ever use them anyway.

The output from the neural net is a VE value which can then be further manipulated by various multipliers for different operating conditions. With NN on, the NN calculates it’s own VE instead using the VE table. The calculation is pre-determined based on input values of rpm, pressure ratio, and a 4th dimension, cam timing. So instead of a traditional 3D VE map, think of the neural net as a 4D or 5D VE map. More inputs, more dimensions.

 

[jonx96]

Speedy I forgot to reply to your question about hacking injector data on the other thread. I was just referring to exactly this. Making the car run not using the proper stoich value.
Digging through forum posts on hp tuners site injector hacking is just what we are talking about here. Does it work. Yes. Do some big named tuners do it this way. Yes. Should these cars be tuned that way? Well that’s where we are inviting discussion. Personally, if I am not a professional and I am spending countless hours to figure out how to properly set this up I would think a professional charging you for a service should do the same. With that being said if I’m just someone tuning my own car and I make good power on the dyno and go out and run a good pass that may be all that matters.

But you know just thoughts from someone who hasn’t built up the courage to start his car up on his own tune yet 😂 I wish I decided to get into this while the car was stock. Now I have a lot more to learn before I get comfortable trying anything.

 

[Speedy!]

@zhc thanks for that info, that explains why I'm seeing what I'm seeing when values in some of these tables are changed. Sounds like they're variables that feed in to NN for decisions. I'm trying to visualize a 4D or even 5D map, I need to noodle on that a bit to get my head around it.

@jonx96 I'm not sure I'd say that's really hacking the injectors, may be splitting hairs though in terminology as all of this is hacking the factory calibration to do things the engineers didn't LOL. There may be a reason some tuners don't rescale stoich for E85. Mike does not and while he trained me I decided to go my own route there. Maybe you get better injector resolution or something I'm not aware of by leaving stoich a lone, or maybe when you're tuning dozens of cars a week you don't have time to explain to every E85 customer why the dash reads 9.x at idle now rather than 13.x it did before . Most people don't get as deep in to this as we are trying to do and don't even data log their car.

I'd try to take a course or find a tuner willing to give you some training before you start changing too many things. I felt I had a pretty good understanding of how the basics worked when I got started, but man did I find I had a LOT to learn and did make some mistakes a long the way. Nothing that would hurt anything but a couple times the car drove real weird after I changed something LOL.

A couple small tips I can offer are to always get the fueling dialed in first before doing anything with timing. You wanna make sure you understand fuel 100% and it's doing exactly what you want (and think) it should be doing first. The other thing is pay attention to the scaling of the tables your working with. They're not all the same and sometimes changing the scaling on one will change it on half a dozen others in the background. By scaling I'm talking about the X and Y axis values.

 

[zhc]

@zhc thanks for that info, that explains why I'm seeing what I'm seeing when values in some of these tables are changed. Sounds like they're variables that feed in to NN for decisions. I'm trying to visualize a 4D or even 5D map, I need to noodle on that a bit to get my head around it.

Maybe this will help visualize? I put this together a while back. Visualizing 4 dimensions. ECA = exhaust cam angle

 

[jonx96]

@Speedy! I’ve been looking for a book to start. I may just end up having to start with the tuning school. Unless anyone knows anything better.

 

[Speedy!]

@zhc yep that helps an some interesting data to boot. Thanks.

@jonx96 I've heard good things about the tuning school. I think Simon is the guy over there that does the classes if memory serves. Aussie guy? Would be a good start anyway. Just make sure they have Mopar specific information as they're different from Ford, Chevy, Nissan, etc.

I'm trying to dissect the tune out of my wife's 2019 Infiniti Red Sport 400. Way different than the Hellcat.

 

[drag racer]

@Speedy! I’ve been looking for a book to start. I may just end up having to start with the tuning school. Unless anyone knows anything better.

I find the Tuning School Dodge-specific books a very good place to start...the first book was the general ECM tuning, and the newest one, for the ZF trans specifically.