LS2/LS7 coils and DWELL Time

[bachig24u]

Hi Matt,
I was curious if there were any developments on this?

KR
Sime

[Matt]

I've not looked into this since. The columns have been fixed up in previous versions but the values of the table do not have a static effect on ms but more as a % change

[supersayianjim]

so i have a type 3 board with ls coil packs. where do i find the map screen to adjust this??

[Matt]

Dwell time / Dwell duty tables

[supersayianjim]

so heres my dwell/duty cycle. I haven't adjusted this since I had stock coils. what do I do with these curves??

[Matt]

What are the specs for the LS coils. You would need to modify the dwell duty cycle table to match

[supersayianjim]

to match what?? the curve on the right??

[Matt]

The one on the left... the one on the right is just compensation for lower battery voltage

[guricha]

does someone has information for duty and dwell for LS1 square style ?

[Matt]

Looking into the LS2 at the moment. Found that the R32 ECU has other constants it checks which affects the maximum dwell time which can be commanded when trying to change these tables

The tables Dwell vs RPM is multiplied by Dwell vs Battery to get the final dwell time. You need a scope to set these properly. However I need to fix up the hard coded constants in the ECU to increase the dwell further. Looking into it now

[bachig24u]

keep in mind the LS2 coils autofire when dwell values exceed specific levels depending on the coil variant.

some LS2 coils will do this at 4.5ms some up to 7.5ms.
As there are quite a few variants of them nowadays its a little hard to know which parts numbers respond in which way.

[Matt]

Yes I read about that one:
http://www.msextra.com/doc/ms3/ignition.html#coils
http://forums.nicoclub.com/my-ls2-ls7-c ... 53832.html

GM LS2 coil wiring
A dwell figure of 4.0ms is advised for LS2 coils.(was 4.5) Note that some coils have a built-in overdwell protection feature. If given too much dwell the coil will automatically spark. This can give a dangerous advanced spark. Be sure to strobe your timing at high revs to ensure this is not happening

Problem with R32 maximum dwell I could get on bench. I did note the ECU double sparked in some situations too

Table below shows the max on the scope:

RPM 800 1600 2400 3200 4000 4800 5600
Value 32 52 70 90 110 127 148
ms (current) 3.5 2.8 2.5 2.4 2.1 2 1.8
ms (Max) 15 6 3.5 2.7 2.2 2.2 1.9

[bachig24u]

yeah, the nicoclub-link sounds like its on the money, we saw similar results at the track.

was it double spark down low like an msd ign systems or sporadic at high rpm top like disaster waiting to happen?

[Matt]

The double actually came from the ECU output itself, prior to the coil. Having too large dwell values in the tables triggered two pulses instead of one. Not sure why but it may be built into the external circuitry in the ECU. Still looking into it

[bachig24u]

Sounds like either a protective fail safe to prevent cooking a coil or a feature to improve emissions at low rpm.
Its not desired or required after about 3000-4500rpm as most average camshaft overlap would be negligible by then.

look forward to finding if its something we can dial in or just a limit imposed by a transistor base current logic getting saturated and collapsing by default.