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Rethinking Total Timing Advance


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Rethinking Total Timing Advance Cadillac LC3 HpTuners #Motorama

Posted on June 1, 2013by bwnunnally

In the tuning process adjusting total timing advance on a modern engine can be tricky. There are timing adjustments coming in from a variety of sources, which may change from one pull to another. To simplify the dyno process, it is inviting to isolate the total timing to a single table and adjust.

The files below relate to my 2008 Cadillac STS-V with the DOHC, VVT, supercharged 4.4L V8 engine:

tunedtiming1-1024x637.jpg

Read More: http://caddyinfo.com/wordpress/rebuilding-total-advance/

Bruce

2016 Cadillac ATS-V gray/black

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The thing that occurs to me is that there are zero knock sensor counts. To me this means that there is at least another degree or two of spark advance to be had.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I agree; I was reading a LSX engine argument that more spark <> more power after a certain range. More experimentation is needed for my car though -- that's how we find out.

Bruce

2016 Cadillac ATS-V gray/black

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Back in my youth I tried 150 octane aviation gas in a street hot-rod two-stroke motorcycle and found that yes, there was a point beyond which advancing the spark peaked the torque, then it actually began to fall off a little. And, I couldn't get the engine to get hot enough to run really well. I tried 100 octane aviation gas and it was better but the engine still ran cold so I went back to pump gas.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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In Pursuit of Max Torque Timing #Motorama

Posted on June 4, 2013by bwnunnally

X06PT-8C011-1024x819.jpg

Each engine has a perfect timing advance across RPM that results in the maximum torque for that engine. GM tucks this info into a table that HPTuners refers to as Max Torque Timing vs RPM vs Cylinder Air — the theoretical timing that provides maximum torque for the engine.

maxtorquetimingvsrpmvscyl.jpg

Max Torque Timeing vs RPM vs Cylinder Air

The advance at various RPM points in this table may not be achievable — there could be knock or detonation at those points at this advance. The PCM uses the table as a reference to determine delivered torque. This is one of the few tables that HPTuners recommends the user not change.

Read More: http://caddyinfo.com/wordpress/in-pursuit-of-max-torque-timing/

Bruce

2016 Cadillac ATS-V gray/black

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The zero knock count explained. If the gas allows it, the maximum torque advance map is what is used. It would be interesting to have torque maps that would overlay this one to understand what the maximum torque versus charge and RPM looks like.

Note that the maximum spark advance in this map is in the cruising RPM and charge range.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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The max torque vs RPM vs cyl air table is only used for reference, not for actual spark. Three other tables are used for operating advance. My theory is that the max torque table may provide a template for how to trim the actual operating tables for best performance.

I did find one article (not on this engine) where the tuner simply pasted the max torque table to his main spark table with worse results, which would be a counter-example.

Bruce

2016 Cadillac ATS-V gray/black

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I'm a little confused by a table that is presented as the "optimum torque spark table" but really isn't. Well, clearly, if that one "maximal torque" table was the optimal spark advance, it would be used except as modified by the knock sensor. There is the build table, which retards the spark by 0 to 2 degrees for you motor that apparently deals with production variations in compression ratio or hot spots. There is the set of sensors such as the ECT, IAT2, mixture variations, etc. So the optimal torque spark table really is the one computed from the sensors and the PCM spark tables, and the one published by Motorama as the "optimum torque spark table" is an example for a given set of sensor inputs and no knock counts?

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I think I agree. Set aside detonation for a moment, which is a separate process. In the absence of detonation, what timing advance would provide the maximum torque at each RPM and Cylinder Air level? That's the Max Torque Timing vs RPM Vs Cylinder Air table. It is used by the engine to estimate the actual delivered torque based on how close the engine is actually running to provided parameters.

The various timing tables tables DO consider detonation, and take into account real world situations -- inputs and stresses and attempt to make power with no detonation.

I agree with your statement that in the real world the max torque one can make without detonation is the max torque because detonation can happen and is to be avoided. The max torque values are also interesting because beyond that torque even in the absence of detonation the engine won't make more power with more timing(?).

Max-Torque-Timing-comparison.jpg

All in all my V engine is running within a couple of degrees most of the time of the max torque timing. That may mean that we're good, or it may mean that with careful tuning it can make more power than it does.

Bruce

2016 Cadillac ATS-V gray/black

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I think what I'm coming to is that the maximum torque map is an ideal that the computed map deviates from due to the sensor inputs such as IAT2 and ECT, and is coordinated with mixture controls and throttle angle or even throttle angle rate of change and RPM rate of change. The interesting thing is that the actual spark advance exceeds the maximum torque spark advance over 6100 RPM.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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This makes a good safe place to experiment -- a reduction in timing could be better.

The max torque vs RPM vs cyl air suggests 24 degrees advance at 6000 and 23 degrees at 6500

The STS-V is running 22.5 degrees at 6000 and 25.5 at 6400 then 22.5 at 6800.

Taking 2 degrees out of the timing at 6400 (moving all the air cyl values in that area to 23 deg) will theoretically make no LESS power, and allow the engine to rev faster from 6000-6400 (this took only 0.484 sec last test).

I also want to try to edge the shift up a bit from 6335 rpm to around 6500 rpm so I am shifting 2-3 from 61 mph to 63 mph and capturing closer to peak Hp in 2nd. Running to fuel cutoff does that well enough but is not good for the engine.

Bruce

2016 Cadillac ATS-V gray/black

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Bruce, would you explain that statement please. "Taking 2 degrees out of the timing at 6400 (moving all the air cyl values in that area to 23 deg) will theoretically make no LESS power, and allow the engine to rev faster from 6000-6400 (this took only 0.484 sec last test)." I am not arguing the point, I just have never heard it before and am curious. (the rev faster part)

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Two points in the sentence:

  • at the max torque point additional timing beyond that point does not cause additional power increase -- it is the timing point of max torque
  • a reduction in timing causes a slight reduction in dynamic compression, which allows the engine to rev faster -- Possibly undetectably small effect.

Bruce

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Testing Toward MBT — 6400 RPM at 23.5 Degrees

Posted on June 7, 2013by bwnunnally

Today’s test is a consideration of if a Cadillac STS-V supercharged VVT DOHC 4.4L V8 will make more power or less power with slightly less timing at 6400 RPM. I am using Hp Tuners to data log and for one graphic, and Virtual Dyno for the other graphic.

Cadillac’s Max Torque vs RPM vs Timing table suggests that 23.5 degrees of advance is ideal at 6400 RPM, but the PCM commands more. So we test and see which is more right.

MBT-Test-2013-06-07-6400.jpg

Read More: http://caddyinfo.com/wordpress/testing-toward-mbt-6400-rpm-at-23-5-degrees/

Bruce

2016 Cadillac ATS-V gray/black

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Testing Toward MBT — New Max Torque

Posted on June 8, 2013by bwnunnally

Today I continued my testing toward MBT by adding timing across the rev range to move the commanded advance closer to the MBT vs RPM vs Cyl Air table. 1 degree of advance was added from 3000-3600 RPM, and 0.5 degrees from 3800-6000 RPM.

The V was cold, in cool air, almost out of fuel.

I went to a less densely populated HPTuners table to gauge if that improved the data capture. My impression is this was useful, but that we are capturing info as fast or faster than the related PID are updating anyway. I would prefer to have the more diverse info points than oversample a smaller set for future tests.

MBT-Retune-2013-06-08-Torque-Graphic.jpg

More timing makes more Torque

This graphic shows today’s delivered Torque in blue, and the previous delivered torque in yellow. The current total advance in red, and previous in green. This shows that by touching up the timing the V gained ~5 lb ft of torque throughout the range.

Read more: http://caddyinfo.com/wordpress/testing-toward-mbt-new-max-torque/

Bruce

2016 Cadillac ATS-V gray/black

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MBT-retune-hp-and-torque-comparison-2013

HPTuners data delivered torque & calculated hp comparison to previous

This graphic is the same info but with calculated HP compared current and previous. The actual high points were:

Previous 541.65 HP at 6585 rpm torque 453.0 lb ft at 3663 rpm

Current 555.78 HP at 6710 rpm torque 471.0 lb ft 3478 rpm

Current 545.6 HP at 6573 RPM

The previous test run topped at 6585 rpm where the 2-3 shift hit; today’s run was for 545.6 hp at a similar 6573 RPM.

Bruce

2016 Cadillac ATS-V gray/black

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That matches the CTS-V ratings. I rode in this car and the feel of the power is very similar to that of the CTS-V.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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