E38/E67 Max Torque Timing Table

[verlon]

Hi everyone!

Today I will tell you what this table is used for to stop speculations about it once and for all.

It is used not for torque calculations!

MBT values from this table in E38/E67 controllers is used only for three purposes:
1. Intake Valve Temperature (IVT) calculation
2. Exhaust Gas Recirculation various temperatures calculaction
3. Catalytic Converter and Oxygen Sensors temperature modeling

Truth to tell, MBT table actually is not MBT table at all. It's a reference table where all those models are factory calibrated. Most model calculations internally use "Spark Advance MBT Delta" parameter which represents difference between MBT and actual Spark Advance. All negative values are clamped to zero. So if you have MBT 55 deg and Spark Advance is 40 deg, Delta will be 15 deg. And if you lower MBT to 35 deg, you'll get zero Delta. That's why lowering values in the MBT table leads to almost no effect, it already has about a half of values close to final Spark Advance even in stock calibration.

The crucial part of this is IVT calculation model because it affects transient fueling and thus overall driveability. Spark Advance MBT Delta has additive influence on IVT with negative derating factor of about -0,6 deg.C per deg spark. So you can increase acceleration enrichment by pulling up MBT which will cause lower calculated IVT and lower Evaporation Factor. But do this very carefully and only to make local changes. Overall AE/DE must be tuned using transient fuel model.

[GHuggins]

It has also been my experience that torque timing is also referenced straight by the torque model to try and get more power output from the engine. In other words if tq timing is higher than high octane timing, which it should be and the torque model is set over what the engine actually makes and the engine isn't registering knock, then it will use the max tq timing table's timing limit to add more timing to the high octane table.

[verlon]

It has also been my experience that torque timing is also referenced straight by the torque model to try and get more power output from the engine. In other words if tq timing is higher than high octane timing, which it should be and the torque model is set over what the engine actually makes and the engine isn't registering knock, then it will use the max tq timing table's timing limit to add more timing to the high octane table.

On torque-based controllers it affects throttle and spark, but in E38/E67 controllers this table has nothing in common with torque.

[GHuggins]

I experimenting with this very table in an E67, so I know the torque model will use it to add timing if need be

2013 ZL1 to be more specific...

[07GTS]

so if my main timing is higher then MBT timing table i should increase the MBT timing table so its just over main spark..? can this help with spark torque correction if it goes a little crazy at low airflow with a cam..? is it freaking out because it wants to adjust spark for more torque but it then see its lower then already delivered causing the up/dn spark swings..? this is in E38, ive thought about adjusting this table but it says not to touch it

[verlon]

I experimenting with this very table in an E67, so I know the torque model will use it to add timing if need be

2013 ZL1 to be more specific...

ECM OS 12653669?
I will look into it for that matter.

[GHuggins]

Looked up the specific OS for the car in question I was testing this on - OS # 12652955

[verlon]

Ok, i'll acquire this OS and look inside.
But I think MBT table influences spark indirectly. When pulling MBT very high you may accidentally activate COT protection under heavy loads.
On the other hand you can't demand torque more than the engine can give, because you have pedal->throttle relationship, but not pedal->torque. How can controller get to know that you need more torque?

[GHuggins]

I was wondering the same thing. I know it wasn't cot because all of that was disabled. I know the car in question was running 1 to 2 less psi of boost with long tube headers and cat deletes so boost torque model was off plus air mass model was increased over what it should have needed. So no idea how it was doing it.

[verlon]

I've got 2013 ZL1 ECM stock flash image.
MBT Table influences all the same things - IVT, EGR Temp, TWC Temp. No connection with torque and spark advance.

I'm still thinking that you've hit some temperature protection (piston, catalyst, oxygen sensors, whatever).

[GHuggins]

Would the torque model affect those calculations. I imagine so. Only reason I ask is because it didn't start adding timing until changing it?

[lt1z350]

So taking a n/a engine adding a blower and not adjusting this table could really screw with transitions from what your explaining? I ask as still have some trans issues on a 07 tahoe with lsa blower on it. The way I got through it was make ve redicilous in the area off idle but trans tables weren't affecting it as it should have like some calculations are drastically off.

[verlon]

Would the torque model affect those calculations. I imagine so. Only reason I ask is because it didn't start adding timing until changing it?

The more you add MBT the more chances that you will get very high calculated exhaust temp and activate some overtemp protection. That's why adding MBT is more noticeable than lowering it.

[verlon]

So taking a n/a engine adding a blower and not adjusting this table could really screw with transitions from what your explaining? I ask as still have some trans issues on a 07 tahoe with lsa blower on it. The way I got through it was make ve redicilous in the area off idle but trans tables weren't affecting it as it should have like some calculations are drastically off.

Adding blower completely changes Exhaust Residual Fraction and thus physical MBT. So it's likely that you have transient fuel problems because of wrong MBT.

[gmtech16450yz]

I just have to add a little bit of humor here. Am I the only one here that immediately thought of this Big Bang Theory skit when you realized Verion was from Moscow? lol.

Seriously Verion, no offense intended, I was thrilled you started this thread and I absolutely love it when guys on here explain tables that don't do what we all think they do. Thank you a TON for that, I had no idea how that table effected IVT calculations. Excellent and very valuable information! And the fact that you're from the other side of the world from a lot of us makes it that much more amazing. The fact that we can all benefit from what others have learned and share information even though we're thousands of miles apart is pretty d@mn cool.

This is the scene I thought of when I read this thread... (skip to 1:50 if it doesn't start there automatically.)

[GHuggins]

The more you add MBT the more chances that you will get very high calculated exhaust temp and activate some overtemp protection. That's why adding MBT is more noticeable than lowering it.

But that's just it... High octane timing or the MBT as your referring to it was already changed and dialed in fairly closely without any timing additions being caused... Changing the torque model caused it to start adding 2 more degrees of timing... I'm thinking there's still something linked here, but could be completely wrong?

[verlon]

But that's just it... High octane timing or the MBT as your referring to it was already changed and dialed in fairly closely without any timing additions being caused... Changing the torque model caused it to start adding 2 more degrees of timing... I'm thinking there's still something linked here, but could be completely wrong?

What exactly have you changed in the torque model?

[GHuggins]

This was in the early days - I only changed the airmass a,b,c&d tables...

Second thought it may have been an overtemp condition - just looked at the tune I did years ago and it had 2 degrees in the cot in this fueling area - not entirely sure why the torque model would have changed the temp calculations though?

[GHuggins]

AND thank you for the explanation on this table - helped open my eyes to what it actually does

[GHuggins]

So if this timing table is just used for temperature calculations - what's the best way to make alterations to it? If it's lower than the timing in the main spark tables, does it effect any sort of maximum allowed timing?