Corvette and Camaro Team Apparently Disagree on the Timing Advances Dependence on AFR

If you look at some of the earlier Corvette LT1 tunes PE/COT Spark Advance Correction (ECM 12634) the earlier (2015) LT1 tunes have to reduce timing at higher EQ ratios (richer). If you look at a 2016 Corvette LT1 tune it has the opposite, increases timing at higher EQ (richer) ratios and decreases at lower EQ ratios (leaner). Now I doubt the Corvette or Camaro development team was involved in the calibration but I would assume it was probably a global powertrain team and they maybe consulted the design team a few times but it was probably there decision? I have also heard the calibrations aren't even made by a human and are somehow automatically (AI? I don't believe there is a such thing as AI) populated based on data collected from engine dynos and the lab. Although I really really doubt GM would let a calibration go to production without letting at least one human look it over and make sure it looks somewhat ok.

Anyway it seems the entire internet and everyone else can't come to a definitive conclusion on spark advances dependence on AFR or if it is even dependent at all? As with everything else I'm sure it just depends and there is no generalization you can follow.

Its also possible that maybe when the table got programmed into HP Tuners someone missed that it was supposed to be in Lambda instead of EQ which would explain why they are opposite each other.

The intake and exhaust are different between the Camaro and Corvette. Throw in the weight difference as well and it is not surprising. But also you need to account for all of the timing logic including the base, PE, adders, IAT, ECT and others. They likely are not that different over all but small differences in final timing can directly be attributed to the vehicle weight itself, the intake and exhaust and even rotating mass. If you look at the ZL1 LT4 vs the Z06 LT4, the Z06 has a more aggressive cylinder pressure(using the variable cam) coming up to peak torque. The Z06 can likely get away with this due to the lighter weight. It's not only about the engine itself.

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Originally Posted by TriPinTaZ

The intake and exhaust are different between the Camaro and Corvette. Throw in the weight difference as well and it is not surprising. But also you need to account for all of the timing logic including the base, PE, adders, IAT, ECT and others. They likely are not that different over all but small differences in final timing can directly be attributed to the vehicle weight itself, the intake and exhaust and even rotating mass. If you look at the ZL1 LT4 vs the Z06 LT4, the Z06 has a more aggressive cylinder pressure(using the variable cam) coming up to peak torque. The Z06 can likely get away with this due to the lighter weight. It's not only about the engine itself.

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Thanks Taz, so I wasn't just talking about a comparison between them but a comparison between the years.

What I am specifically talking about is the PE/COT timing correction table:

This is from a 2017 Corvette:
Attachment 101484

This is from a 2015 Corvette:
Attachment 101485

Notice how the positive and negative timing are switched, from looking at some other LT1 Camaro and L86 truck tunes, it appears to me the only ones I can find is just this one on the 2015 Corvette. So basically on the 2015 for higher EQ ratios (richer) it is pulling timing, for lower EQ ratios (leaner) it is adding timing. All the other tunes I look at are consistent with the way the 2017 Corvette tune is, adding timing at higher EQ ratios.

I think what is going on here is that GM made a change in the code in the calibration to where in 2014-2015 they defined this table in Lambda, and then changed in 2016+ or so to define this table in EQ ratio.

Now from a scientific perspective do richer mixtures generally require less timing advance (so they "burn" faster)? Or is it the opposite? Or is there no dependence? I've seen statements on the internet arguing both so I don't know who to believe, but personally I think richer mixtures do burn faster and therefore require less timing, it makes sense from a chemistry/statistical standpoint in that a random point in a richer mixture you are more likely to have a fuel and oxygen molecule run into each other so more chances of a chain reaction starting up sooner in a richer mixture.

Looking at those graphs.. it seems like you would never realistically be in any of the ranges that are not already 0.0 mostly?

Am I missing something?

That is true on the 2017 graph, except for very cold starts where it goes richer than it does since stock PE is in the 1.15+ EQ range.

But there are other years where the stock calibrations have adder tables that you would definitely be in at WOT.

I just really think someone missed something here and its really supposed to be in Lambda, this just makes no sense if it isn't, I know most people just look at the stock calibrations and don't really care if it dosen't make sense, but to me it has to, the stock calibration isn't just something that GM is going to throw together and not even care, its something they are about to release to thousands of cars and it would cost them millions having to recall it and pay for techs to reprogram or even worse if they had to pay EPA fines or something else happened.

The Spark multipliers for 2017+ Corvettes were updated in multiple tables. The final spark values are pretty much identical but the logic was changed around some specifically for Air intake and Coolant temps. It is not uncommon for some years to vary this way. Emissions guidelines changed around this time as well so I suspect there was some logic changes around that. Later year Corvettes and Camaros also allow Cat Lightoff to happen at much higher coolant temps. It used to only be active on cold start if your coolant temp was below 107 F (IIRC) and later years that changed to 151 F or so.

Thank you Taz, I never tested each one to see what the actual timing value came out to be on each one (including the adder tables we don't see). Its almost like the GM calibrator was too lazy to go and re code this adder so they just added it to another table when they needed it disregarding what that tables purpose is actually for. Its bad because it makes me trust the stock tunes that much less.

I can tell you that common logic within understanding GM's structure goes right out the door. Each division has there own calibrators and the only thing shared is sensor control functions and the Global Architecture of the controller. We had been seeing this for years just looks at the trucks vs the cars. Back in the mid 90's trucks would do all kinds of weird stuff a Vette wouldn't do with respect to timing control and how they used to control torque management.

You would think they would have a centralized power train division that include calibration but its not how they work....

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Originally Posted by Redline MS

I can tell you that common logic within understanding GM's structure goes right out the door. Each division has there own calibrators and the only thing shared is sensor control functions and the Global Architecture of the controller. We had been seeing this for years just looks at the trucks vs the cars. Back in the mid 90's trucks would do all kinds of weird stuff a Vette wouldn't do with respect to timing control and how they used to control torque management.

You would think they would have a centralized power train division that include calibration but its not how they work....

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Just like there's 2 different versions of the LT4. ZL1/ctsV and the Corvette platform. Even the calibrations are different.

That discrepancy in the PE spark adder is an HP Tuners definition file problem. There are a lot of them if you have a keen eye. The vast majority of GM's core software is shared among almost all powertrain controllers for a given software architecture. It goes through periodic evolutions as applications and the EPA require.

Thanks everyone for the info. That's interesting that the calibration is done by each design team. In some way that kind of makes a little sense so they can find tune things for their customer base but dosent really make sense from an emission standpoint.

That kind of leads into another question, are the parameters we see in hp tuners set up the same way the calibrators see it? I would assume there is the upper level tables which is exactly the same stuff we have access to and then there is the lower level code that is developed by a global team and even the design team calibrators can't change. What I'm trying to get at is there only certain tables available to the calibration team to where they would "have everything they needed" to properly set up a vehicle? What I'm trying to figure out is if we have access to everything we need to properly tune, I know they are always adding more parameters, but how does HP Tuners know what all we need without doing extensive testing with all kinds of aftermarket hardware, without it already been figured out because it is nicely organized in the tunefile and broken up into upper level calibration tuning parameters and lower level code that runs core functions that's off limits because it's not needed.

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Originally Posted by smokeshow

That discrepancy in the PE spark adder is an HP Tuners definition file problem. There are a lot of them if you have a keen eye. The vast majority of GM's core software is shared among almost all powertrain controllers for a given software architecture. It goes through periodic evolutions as applications and the EPA require.

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Are you saying you think I am correct in thinking that HP tuners messed up defining this table and confused EQ ratio with lambda and that's why it goes against the normal theory of richer = faster burn = less timing advanced needed?

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Originally Posted by cmitchell17a

Thanks everyone for the info. That's interesting that the calibration is done by each design team. In some way that kind of makes a little sense so they can find tune things for their customer base but dosent really make sense from an emission standpoint.

That kind of leads into another question, are the parameters we see in hp tuners set up the same way the calibrators see it? I would assume there is the upper level tables which is exactly the same stuff we have access to and then there is the lower level code that is developed by a global team and even the design team calibrators can't change. What I'm trying to get at is there only certain tables available to the calibration team to where they would "have everything they needed" to properly set up a vehicle? What I'm trying to figure out is if we have access to everything we need to properly tune, I know they are always adding more parameters, but how does HP Tuners know what all we need without doing extensive testing with all kinds of aftermarket hardware, without it already been figured out because it is nicely organized in the tunefile and broken up into upper level calibration tuning parameters and lower level code that runs core functions that's off limits because it's not needed.

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the amount of tables that we see with HPT isn't even a scratch to what is really in a cal. An E92 controller cal is probable close to 7500-8500 parameters. Something as simple a MAP sensor could have 20-30 in just defining the MAP sensor. GM uses "rings" to group each segment such as spark, fueling, etc.. even though they basically function the same between models its more about how each team cross connects the rings.

You have to remember when you make a change in HPT is not unlikely that the changed value is also shared by tables and maps we cant see. We are lucky we have what we have for OEM calibration work!

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Originally Posted by Redline MS

the amount of tables that we see with HPT isn't even a scratch to what is really in a cal. An E92 controller cal is probable close to 7500-8500 parameters. Something as simple a MAP sensor could have 20-30 in just defining the MAP sensor. GM uses "rings" to group each segment such as spark, fueling, etc.. even though they basically function the same between models its more about how each team cross connects the rings.

You have to remember when you make a change in HPT is not unlikely that the changed value is also shared by tables and maps we cant see. We are lucky we have what we have for OEM calibration work!

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Thanks redline, I often do take the side of caution and completely leave stuff alone and stock since I feel like it could inadvertently change something else I am not aware of.

To put it more simple my main question was that how did HP Tuners know which tables we needed access to to get everything running right? Or did they not "know" and we are missing tables we need? Or maybe its somewhere in the middle and we have the basic stuff we need but not the more advanced stuff we need for superior driveability. I know it seems in order for HP Tuners to test if they have all the right tables uncovered and all the combinations of different things that could happen seems like a complete nightmare, unless of course they had someone "on the inside" haha, or they hired the OEM calibration engineers themselves. I bet they had to sign NDAs with the OEMs though.

HPT never claims to be calibrators. There a software development company. This doesn't mean that they have no idea of the logic works as years of experience in what they do has given them enough insight as to what is needed. With all the vehicles/controllers then support it would take an army to add all of the tables. There are files called A2L files which are the road map to all the tables in a given cal but those files are very hard to access. HP needs to stumble across tables or if you can provide the HEX address and pertinent axis info they can add it.....we break there balls about whats missing but do you really know what your looking for? LOL...

Often GM groups parameters so when the find spark tables other spark tables are usually close to the basic ones we use... hopefully this make some sense

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Originally Posted by cmitchell17a

Are you saying you think I am correct in thinking that HP tuners messed up defining this table and confused EQ ratio with lambda and that's why it goes against the normal theory of richer = faster burn = less timing advanced needed?

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I don't know if they confused one for another...likely just fat-fingered something. It happens. The gen 4 throttle follower torque tables have had the Park and Reverse rows swapped for as long as I can remember.

Thanks guys for the help, I think the main thing I was wondering is does richer always mean that more timing is needed? (in general terms of course) or is it the other way around?