Wanted to post the results of some timing tests that Dave and I just finished. First some intro, then the tests, then the discussion 
. Dave has been making measurements on a bench, looking at the time delays between crank senor and est events, to directly measure the ignition timing. His data contains two surprises: the timing can be many degrees higher than the chip commands, and the timing generally increases with rpm above the maximum rpm in the main timing map (4800). This increase is over 10 deg in some chips, for a total timing of 30-40 deg at 6000 rpm in some chips where the timing map indicates a maximum advance of 22-24 deg. For more on Dave's tests, see http://www.turbobuick.com/forums/showthread.php?threadid=46755&referrerid=746 . This is drastically different from what we believe the result will be when we set a timing value in the chip, and I wanted to determine what the actual relationship between chip and spark is on my car.
To investigate this, I made a chip from the stock image that came in my 86 ttype with some changes. The injector constant is set to 75.25 lb/hr so I can run it (I have 72's). The entire main timing table has been set to 20 deg ($57), the coolant bias table has been set to 15.12 deg which cancels the base bias value for a net of zero, the WOT spark table set to 20 deg, the MAT advance correction table left at zeros, the tcc locked correction table left at zeros, the burst knock retard set to zero, highway mode advance table set to zeros, boost spark left at zero, P/N advance left at zero, and all the spark decays left alone. Just for grins I left the ALDL advance increment at $316D set at 8 degrees since the ecm will not be in ALDL mode during this test, but every other advance-related parameter was set so that the timing would be 20 deg at all times. The checksum is $A221 if you want to recreate this and verify it. Dave burned a chip with this image and tested it in his bench setup, with these results:
MAT=80* Engine Temp=190*
TPS=4.8v Speed =30 MPH
LV8=255 MAF=255
RPM Actual Timing Prom Timing
800 20.7 20
1000 20.9 20
1200 21.0 20
1400 21.1 20
1600 21.4 20
1800 21.5 20
2000 21.7 20
2200 21.9 20
2400 22.3 20
2800 22.3 20
3200 22.6 20
3600 23.1 20
4000 23.3 20
4400 23.7 20
4800 24.2 20
5000 24.5
5500 24.8
6000 25.4
7000 25.7
8000 27.1
Next, I ran this chip on my car while checking the timing with a SnapOn timing delay light set to 40 deg (divide by two for waste spark so 20 deg) to bring the timing mark to zero on the timing tab. Idling it was about 1 deg off, showing 21 deg, so there's a little slop somewhere between crank sensor, balancer keyway, and timing chain. DirectScan showed the advance to be over 23 deg at startup but this decayed to 20 in about a minute, and the advance was exactly 20 the rest of the time the engine was running. Coolant temperature was about 165 deg F at the start and 200 at the end. My estimate is that I should be able to see a change of 0.5 deg. Revving up in park the timing dropped 5-6 deg for less than a second and then was rock steady exactly at 21 deg all the way to the rev limiter at 5600 rpm. LV8 got as high as about 65-75, and the tps was under 3 V. Took about 2-3 seconds to go from idle to 5600. Repeated with a little less tps and stopped at 4600, with the same result. Second test was to brake torque up in gear. Here I got to about 3400 rpm and lv8 was 255 from 2400 or so on up, with tps again between 2 and 3.5 V. Boost peaked at about 12 psi with no tire spin. Spoolup was typical for my car, about 3-4 seconds to go from idle to 12 psi, and I held it there for another couple of seconds. Again, timing was rock steady at 21 deg by the light and 20 by DS.
Okay, that's the raw data, now for the discussion. I would have easily seen a change of 5 deg going from idle to 5600 rpm in park and I saw no change. This covers most of the rpm range but lv8 is lower than in Dave's case. The boost test gets lv8 up to 255 as in Dave's case but the rpms only go up to 3400. However, again, I would have seen a 3 deg change. DS showed that the commanded advance was 20 deg no matter what the tps, coolant, rpm, and lv8 readings were, so I am satisfied that I would have seen the change Dave did if it occurred. There was also no evidence of jitter greater than 0.5 deg. I don't know why the timing dropped for a second because the bkr retard was set to zero, but after that first second the timing was steady back at 21 deg indicated. My conclusion from all of this is that the spark advance at the plug is what the chip commands it to be, with no extra advance over 4800 rpm. I have no evidence of the behavior over 6400 rpm where the rpm value in the ecm overflows.
. Dave has been making measurements on a bench, looking at the time delays between crank senor and est events, to directly measure the ignition timing. His data contains two surprises: the timing can be many degrees higher than the chip commands, and the timing generally increases with rpm above the maximum rpm in the main timing map (4800). This increase is over 10 deg in some chips, for a total timing of 30-40 deg at 6000 rpm in some chips where the timing map indicates a maximum advance of 22-24 deg. For more on Dave's tests, see http://www.turbobuick.com/forums/showthread.php?threadid=46755&referrerid=746 . This is drastically different from what we believe the result will be when we set a timing value in the chip, and I wanted to determine what the actual relationship between chip and spark is on my car.To investigate this, I made a chip from the stock image that came in my 86 ttype with some changes. The injector constant is set to 75.25 lb/hr so I can run it (I have 72's). The entire main timing table has been set to 20 deg ($57), the coolant bias table has been set to 15.12 deg which cancels the base bias value for a net of zero, the WOT spark table set to 20 deg, the MAT advance correction table left at zeros, the tcc locked correction table left at zeros, the burst knock retard set to zero, highway mode advance table set to zeros, boost spark left at zero, P/N advance left at zero, and all the spark decays left alone. Just for grins I left the ALDL advance increment at $316D set at 8 degrees since the ecm will not be in ALDL mode during this test, but every other advance-related parameter was set so that the timing would be 20 deg at all times. The checksum is $A221 if you want to recreate this and verify it. Dave burned a chip with this image and tested it in his bench setup, with these results:
MAT=80* Engine Temp=190*
TPS=4.8v Speed =30 MPH
LV8=255 MAF=255
RPM Actual Timing Prom Timing
800 20.7 20
1000 20.9 20
1200 21.0 20
1400 21.1 20
1600 21.4 20
1800 21.5 20
2000 21.7 20
2200 21.9 20
2400 22.3 20
2800 22.3 20
3200 22.6 20
3600 23.1 20
4000 23.3 20
4400 23.7 20
4800 24.2 20
5000 24.5
5500 24.8
6000 25.4
7000 25.7
8000 27.1
Next, I ran this chip on my car while checking the timing with a SnapOn timing delay light set to 40 deg (divide by two for waste spark so 20 deg) to bring the timing mark to zero on the timing tab. Idling it was about 1 deg off, showing 21 deg, so there's a little slop somewhere between crank sensor, balancer keyway, and timing chain. DirectScan showed the advance to be over 23 deg at startup but this decayed to 20 in about a minute, and the advance was exactly 20 the rest of the time the engine was running. Coolant temperature was about 165 deg F at the start and 200 at the end. My estimate is that I should be able to see a change of 0.5 deg. Revving up in park the timing dropped 5-6 deg for less than a second and then was rock steady exactly at 21 deg all the way to the rev limiter at 5600 rpm. LV8 got as high as about 65-75, and the tps was under 3 V. Took about 2-3 seconds to go from idle to 5600. Repeated with a little less tps and stopped at 4600, with the same result. Second test was to brake torque up in gear. Here I got to about 3400 rpm and lv8 was 255 from 2400 or so on up, with tps again between 2 and 3.5 V. Boost peaked at about 12 psi with no tire spin. Spoolup was typical for my car, about 3-4 seconds to go from idle to 12 psi, and I held it there for another couple of seconds. Again, timing was rock steady at 21 deg by the light and 20 by DS.
Okay, that's the raw data, now for the discussion. I would have easily seen a change of 5 deg going from idle to 5600 rpm in park and I saw no change. This covers most of the rpm range but lv8 is lower than in Dave's case. The boost test gets lv8 up to 255 as in Dave's case but the rpms only go up to 3400. However, again, I would have seen a 3 deg change. DS showed that the commanded advance was 20 deg no matter what the tps, coolant, rpm, and lv8 readings were, so I am satisfied that I would have seen the change Dave did if it occurred. There was also no evidence of jitter greater than 0.5 deg. I don't know why the timing dropped for a second because the bkr retard was set to zero, but after that first second the timing was steady back at 21 deg indicated. My conclusion from all of this is that the spark advance at the plug is what the chip commands it to be, with no extra advance over 4800 rpm. I have no evidence of the behavior over 6400 rpm where the rpm value in the ecm overflows.
