gojo

I posted this in Tuning. Maybe someone here knows.
I have an LS7 crate engine in a 2003 C5. The Spark Dwell Time for the LS7 is lower than for the LS1. I'm using the LS7 table since I don't want to burn up the LS7 coil packs.
It doesn't seem to outwardly make any difference which table I use.
Any reasons why the LS7 times are lower?

edcmat-l1

Are the coils different part numbers? It may be that the LS7 coils have a different number of windings which would require less saturation time to achieve the same or more secondary output.
Just hypothetical.....
For that matter, next LS7 we get I'll scope the primary and secondary (voltage), and the coil saturation, in both time and amperes.

gojo

The coil packs are different with different #'s. I've heard they are better, but haven't heard in what way. I suspect that you're right about them needing less dwell time to create the necessary spark.
The LS1 packs require 4-5 times the dwell at low voltage and high RPM's. But as we get closer to 13 volts the dwell table values are less than 2x at high RPM's.
I don't think there are any other factors influencing the output, but it would be nice to be certain.
Thanks for the response. I would be very interested in what you find.
Joe

Tony @ MPH

Not a lot of guys doing LS7 swaps *and* looking at ancillary tables like the spark dwell table -- I hope that you find a clear/concise answer but suspect that you won't. Trial and error is what this is probably going to boil down to.

I think that the worst that could happen with insufficient dwell time (e.g., using the lower LS7 table) is you will get weak or no spark, which will become apparent during tuning. Unfortunately, an aggressive dwell time may not be apparent until a few months later when coils mysteriously start going bad.

Good luck and let us know what you end up doing!

gojo

I've been using the LS7 table so as not to hurt the coils. There have been no noticeable issues at all. No hard starts, no missing or backfiring and it is surprisingly smooth and easy to tune. I wonder if it would show up as a loss in power on a dyno?

Thanks for the feedback
Joe

edcmat-l1

On the contrary, using an o-scope, you can determine several things about an electrical coil, whether ignition, injector, etc.
Saturation, both amount of amperage draw, and time it takes to saturate completely (the latter being the most important in this case). There are seemingly insignificant portions of the waveform that mean specific things.
The first few micro seconds of the amp ramp, as the electrons "rush in" and begin the saturation process, makes a specific pattern that directly relates to integrity of the primary side, and the clear seperation from the secondary side.
This is done using an inductive amp probe.
At the same time, using a second channel on the same scope, you can view the primary voltage, and determine several things about that as well. The integrity of the switching device, whether its a current limiting system or not, integrity of the secondary side (yes, from the primary side voltage) etc.
Using a third channel (4 channel scope, all of this is being plotted at the same time) you can monitor the secondary voltage.
And as the primary collapses, and the coil fires the secondary side, you again can determine several different things. secondary coil integrity, resistance of the plug wire, plug itself, and even a little about whats happening inside the cylinder. the plug firing line portion of the pattern will look different depending on cylinder pressure (low comp, hi comp) fuel mixture (lean or rich) and how wide the plug is gapped.
I have actually scoped ignition systems and made DEAD ON diagnosis of things like bad coils, closed plug gaps, lean conditions from injector flow problems, verbally, before ever pulling a part!!
So, basically, you can determine why there is a difference in the dwell time, using these techniques, and information. If they are different part numbers, they will probably act diffferently electrically.

gojo

Ed,
Can we determine which values are correct without knowing what the result should be?
Joe

edcmat-l1

No...not without knowing how they are functioning electrically.
The important part of all that blah that I posted, is the length of time they take to saturate.
What you would see, on a scope, from one coil to another, would be a difference in the amp ramp. Which is nothing more than a picture of the rate of electron flow into the primary coil. Or more commonly called, saturation.
Ignition coils arent supposed to reach complete saturation. Some peak sharply before discharging. Some flatten out on top. But its the inclination of the ramp that tells the story of the resistance and total winding of the primary. I'll pm you a couple ignition amp patterns tomorrow. I have several hundred scope patterns of all sorts I've been saving up over several years. I'll make sure to get a hold of a ls7 just to check this out.
I was aware of the coil dwell tables, but didnt know the dwell time was different from ls1 to ls7.
You got my curiosity up now.
PS saw your same thread on ls1tech. not much info over there

Tony @ MPH

Sorry, I didn't mean to sound like the ONLY approach one could take in this situation was trial and error. With the right knowledge and equipment, there's always a way to dissect this stuff, and I'm both intrigued and impressed by your post.

Still though, I think the net result is that gojo is no closer to knowing what the exact values should be -- am I right? But by analyzing the amp ramp rate he could tell if the reason why the calibration tables are different is due to the coils, or something else in the ignition.

Although I love to know the "why" just because I am a tinkerer at heart, it still seems like the fastest approach to knowing which dwell table is more correct is to use the least agressive one and see if it leads to ignition related tuning problem.

Or am I way off base on that?

Always eager to learn,
Tony

gojo

This is the LS7 table. At these volts the tables are closer.
.RPMS................LABELS.......Volts
...........11.0.........12.0......13 .0.......14.0......15.0
.....0 5.091165 4.392080 3.890562 3.465032 3.145884
..400 4.984783 4.346488 3.875365 3.465032 3.130687
..800 4.893598 4.270500 3.860167 3.449834 3.130687
1200 4.863203 4.300895 3.829772 3.434637 3.100292
1600 4.832808 4.255302 3.784180 3.373847 3.054699
2000 4.711228 4.164117 3.708192 3.313057 3.009107
2400 4.422475 3.905760 3.465032 3.085094 2.781144
2800 4.331290 3.844970 3.419439 3.039502 2.750749
3200 4.240105 3.768982 3.343452 2.993909 2.705157
3600 4.148920 3.692995 3.297859 2.948317 2.674762
4000 4.027340 3.601810 3.221872 2.887527 2.613972
4400 3.966550 3.556217 3.176279 2.841934 2.568379
4800 3.799377 3.404242 3.039502 2.735552 2.492391
5200 3.601810 3.221872 2.887527 2.598774 2.370811
5600 3.389044 3.054699 2.735552 2.461996 2.249231
6000 3.237069 2.917922 2.629169 2.386009 2.188441
6400 3.130687 2.841934 2.583576 2.355614 2.158046
6800 2.948317 2.674762 2.431601 2.218836 2.036466
7200 2.735552 2.492391 2.264429 2.066861 1.899689
7600 2.537984 2.325219 2.112454 1.930084 1.778109
8000 2.401206 2.218836 2.021269 1.854096 1.717318


LS1 table

LABELS........................Volts
RPM.......11.0........12.0........13.0.. ....14.0......15.0
....0 5.243141 4.498463 4.042537 3.601810 3.297859
.400 5.243141 4.498463 4.042537 3.601810 3.297859
.800 5.243141 4.498463 4.042537 3.601810 3.297859
1200 5.243141 4.498463 4.042537 3.601810 3.297859
1600 5.243141 4.498463 4.042537 3.601810 3.297859
2000 5.243141 4.498463 4.042537 3.601810 3.297859
2400 5.243141 4.498463 4.042537 3.601810 3.297859
2800 5.243141 4.498463 4.042537 3.601810 3.297859
3200 5.151955 4.407278 3.996945 3.601810 3.297859
3600 5.106363 4.407278 3.996945 3.601810 3.297859
4000 4.999980 4.300895 3.905760 3.495427 3.252267
4400 4.954388 4.300895 3.844970 3.404242 3.206674
4800 4.848005 4.194512 3.753785 3.297859 3.100292
5200 4.848005 4.194512 3.692995 3.206674 2.993909
5600 4.848005 4.194512 3.692995 3.206674 2.993909
6000 4.848005 4.194512 3.692995 3.206674 2.993909
6400 4.848005 4.194512 3.692995 3.206674 2.993909
6800 4.848005 4.194512 3.692995 3.206674 2.993909
7200 4.848005 4.194512 3.692995 3.206674 2.993909
7600 4.848005 4.194512 3.692995 3.206674 2.993909
8000 4.848005 4.194512 3.692995 3.206674 2.993909

Tony @ MPH

Gimme a minute and I'll pull my LS6 tables just for extra info. I suspect it will be the same or very similar to your LS1 tables.

Tony @ MPH

Yep -- my LS6 table matches what you posted from your LS1 table.

edcmat-l1

Not off base at all. Actually dead on. Even knowing the ramp up rate using an o-scope, doesnt necessarily mean that X amount of time is ideal, but it does give you a great deal of insight.
And you have to be able to determine, using all this new found info, if increasing or decreasing the dwell time is having the effect on the secondary side that you want (increased voltage discharge) and whether or not its harming the coil.
Although the secondary voltage output is determined by the resistance of the secondary side. The voltage required to jump the gap.

edcmat-l1

In this image, focus on the left side of the screen. This is a DIS setup, and the second amp ramp is waste spark.
This first image is of the primary voltage and current flow (amperage) of an ignition coil when its cold. This car had misfire issues after it got hot. notice how the amp ramp was steep, pointed at the top, and has a clean discharge, the falling edge on the right.
The sharp peak means the coil never reached complete saturation (which it shouldnt)
The voltage on channel 1 show the coil being switched on (grounded) and then released from ground and the corresponding spike from the primary coil collapsing. If the secondary had issues such as high resistance, this is where it would show up. On the falling side of the amp ramp, and the right side of the voltage wave.

Again, looking at the left side of the screen, you can see that after the vehicle got hot, something changed. The triggering device (pcm, or ign module) went into current limiting mode, evidenced by the step in the primary voltage (channel one) and the flattening out of the amp ramp. You can clearly see how the two coincide. This is a built in protection mechanism.
Right before the ignition switching device went into current limiting, you can see how the amp ramp changed angles, indicating a change in resistance.

edcmat-l1

This is the first few micro seconds of an amp ramp. This is a bad ignition coil.

Same vehicle, good coil. The little squigglys (technical term) are what you want to see. I just know if the arent there, or if theres just a couple, theres something wrong with the primary side of the coil. Mainly, an open in the winding.

gojo

Ed,
Interesting stuff. It would be nice if I could do it.
Can I change spark dwell and see results on a dyno, if there are any resulting changes.
I've been looking for spark dwell modifiers in the LS7 file. There is a "spark dwell temperature" modifier table that the LS1 doesn't have. The changes are out to 2 decimals. Is that amount significant?
Joe

edcmat-l1

I dont know on the spark dwell temp.
As for seeing results on a dyno, there shouldnt be any improvement unless you're starting with insufficient spark.

gojo

Okay, so if for some reason the LS7 table is too low then raising dwell would show up on a dyno?

Spark dwell multiplier:
LABELS..............................Volt s
Coil Temp °C
.............11..........12..........13. .........14........15
-40 0.878917 0.894543 0.910168 0.925793 0.933606
-25 0.878917 0.894543 0.910168 0.925793 0.933606
-10 0.878917 0.894543 0.910168 0.925793 0.933606
5 0.878917 0.894543 0.910168 0.925793 0.933606
20 0.878917 0.894543 0.910168 0.925793 0.933606
35 0.898449 0.910168 0.921887 0.933606 0.941418
50 0.914074 0.925793 0.933606 0.945325 0.953137
65 0.929699 0.941418 0.949231 0.957043 0.960950
80 0.949231 0.953137 0.964856 0.968762 0.968762
95 0.968762 0.972669 0.976575 0.980481 0.984388
110 0.988294 0.988294 0.988294 0.988294 0.988294
125 0.980481 0.984388 0.988294 0.988294 0.988294
140 0.917980 0.941418 0.964856 0.988294 0.988294
155 0.917980 0.941418 0.964856 0.988294 0.988294
170 0.917980 0.941418 0.964856 0.988294 0.988294
185 0.917980 0.941418 0.964856 0.988294 0.988294
200 0.917980 0.941418 0.964856 0.988294 0.988294

edcmat-l1

IF the dwell was insufficient enough to cause less than adequate spark, causing incomplete combustion.
That being said, if you're using LS7 coils, I would use LS7 tables.
Same goes for LS1 coils. Use the corresponding tables.

gojo

I'm with you. It's been informative. Thanks to all.