240z, yes, the same tables but with correct scaling applied, with the rpm threshold parameter added.

Some scalings you probably already have, like RMPLimit, BatteryVoltage and Percent128, but check or add/replace.

 

Merlin,

Have you decided what the unit is? If I didnt know better I would think its either crank degrees or some raw form of a value for crank degrees of charge time. I run it at 69 to 70 all the way to 16v on my car right now without incidents even at 40+ psi. The gap is still only 0.020 in my heat range 7s.

Aaron

 

The units are milliseconds, so your raw value of 70 = 4.48mS.
However, that will only hold to 2800rpm, if the stock rpm threshold is still being used.
Higher rpm will then see the dwell-time start reducing.
So by 8000rpm the dwell-time will have reduced down to something less than 3mS.

If you look at the first correction table (what I am naming Dwell-Time Reduction Factor because it is a multiplier) the stock raw values range from 57 down to 9 (the correct scaling is x/256).
What I am suggesting is set the 9.38 to 11.72 values to zero for no dwell-time reduction at low battery levels.
And set the higher values to something less than stock and use the same value across the table. A raw value in the range 9-15 should be a good starting point.

 

Just made a change to the CF256 scaling to assist with this. Changed the increment to 0.0039 which allows a one step inc/dec.

 

Merlin,

I cannot seem to find where you defined the calculation to determine actual mS of dwell at a given rpm (say 8000) based on dwell time reduction factor.

For example, I am using the base dwell value provided by Aaron of 4.42ms. If I used a value of 15 (15/256=.0585) for all cells above 11.72V, what would be the formula to determine dwell at 8000rpm?

 

The equation I am currently using (which may have some errors) goes like this:

The base Dwell-Time from the first table at 14.06V=3.46mS. Call this the base Dwell-Time.
This value gets used below the DwellCompRPM which is 2800rpm on Evos5-9.

As Ceddy has indicated it is different on DSMs, specifically 1700rpm, which use different coils.
It is also different on some AUDM stuff I have looked at. No matter.

To get the dwell reduction, multiply the base Dwell-time by the 14.06 Volt value from the second table (The Dwell-Time Reduction Factor table). This table has a CF of 256 applied, so
0.137*3.46 = 0.474

Now, subtract 2800rpm from the target rpm, divide by 2000 and multiply the result with 0.474.

Finally, subtract this from the base Dwell-Time for the final rpm dependant result in ms.

I know it looks messy but the predicted results seem to reasonably match the logged dwell.

 

so, for 240Zs example, base dwell=4.42mS, factor1 = 0.0585

4.42*0.0585 = 0.25857

8000-2800 = 5200rpm

5200 / 2000 = 2.6

2.6*0.25857 = 0.672mS

4.42 - 0.672 = 3.748mS final Dwell-Time

 

Best way to go about this would be simply to log dwell and then adjust the values to get the log to match what you are after.

Keep in mind the high RPM dwell will never be higher then the low RPM dwell.

Something that is weird to me here though, dwell time is independent of cylinder and RPM conditions (provided dwell time isn't so long that it runs into the next ignition cycle). Why does the ECU reduce dwell time at high RPM?

Simply trying to control coil heat maybe?

 

Merlin,
Thank you for you help and quick response. The reason I am trying to understand this better is that I am going to ditch the spoolin COP so I can choose coils that have desired/known performance parameters.

I have purchased 4x AC Delco D514-A "LS2" coils, which are used on a wide range of Chevrolet applications including the Z06 and ZR1 Corvette. The dwell times as a function of battery voltage are available and they are supposedly very powerful units.

The last piece of information I am trying to understand is "Dwell Time Correction 2." However, I guess that if I can just log dwell I can play around with this parameter until I have the desired settings. Thank you again and I will update my progress on this swap.

 

I don't see this in EVOScan...am I blind?

 

No, not blind, add this script to your EvoScan MUTII xml.
I suggest place it straight after RPM and keep the logged items to a minimum if experimenting with dwell settings.


<DataListItem DataLog="Y" Color="" Display="Dwell-Time" LogReference="Dwell" RequestID="2D" Eval="0.064*x" Unit="mS" MetricEval="" MetricUnit="" ResponseBytes="1" GaugeMin="0" GaugeMax="16" ChartMin="0" ChartMax="16" Notes="" Priority="1" Visible="False" />

 

Tweaking the Dwell-Time Reduction factor table and logging the result will certainly get you there with minimal fuss, though the logged values do fritz arround a bit.

To help reduce the jittering (I believe caused by battery voltage changing) set the 12.89V, 14.06V and 15.23V settings (both tables) to the same value while experimenting.

The third table to me is looking like a maximum dwell duty cycle table.
I am confident the scaling is Percent128 though I dont know exactly what its doing.

Additionally, the 1D parameter befor the rpm threshold is also involved somehow.
It is a time thingy equal to 60uS but unknown application/math.

 

Here is a link to decent article on old school ignitions and some gernal info. about CDI ignitions. They talk about dwell and reasons why dwell might be adjusted at higher RPM's not to mention why MSD (multiple Spark discharge) use multiple shorter pulses rather than longer ones to overcome limitations of single charge.
http://www.jetav8r.com/Vision/Ignition/CDI.html

I also remember reading an EvoM thread about a "cheap" dual coil conversion that aimed to provide more spark but not sure about coil resistance etc.. but I'm thinking they were GM coils and the primary was selected as to keep resistance simalar to stock for compatability reasons.

I'm in to see where this goes and thanks to those that put in mega effort to benefit others like me

 

If 4 coils requires half the dwell time of the stock 2 coil setup, does that mean those with spoolinup or other 4 coil kits should be approximately halving those values in the first table?

 

I run them all the same when I set them up. I havent noticed having to change anything one way or the other. Coils dont seem to heat up, havent worn any out, and still have enough fire for 40+psi.

Aaron