Ideal milliseconds per spark on LS1

[forcefed86]

How is the ideal spark duration calculated? This indicates you have 2.5ms for a V8 at 6k. I'd like to the ideal ms range for a V8 at 7000? It looks like the default tune has the MAXIMUM SPARK DURATION set at 1ms. Which seems wrong. Trying to milk all I can out of the smaller square truck coils. (D581 I believe). I have my dwell set at 4ms in the upper RPM. I'm sure I can bump this too as I don't believe the square coils auto fire above "X" dwell setting like the heat sink D-585 coils do.

Having a coil per cylinder configuration allows for longer dwells and stronger sparks at high rpms. For example, an 8-cylinder 4-stroke engine at 6000 rpm (= 100revs/sec), has 400 sparks per second, or 2.5 milliseconds per spark. If there is only one coil, the dwell AND spark must fit into this time, and as a result the dwell is often cut short from its ideal value, and the sparks get weaker. With COP, the sparks only have to occur every two revolutions per plug, so the dwell+spark can be up to 20 milliseconds (8 times longer), and this generally is more than enough time to optimally charge the coil for a full spark. (For wasted spark, there would be 10 milliseconds.)

[billr]

It's best done with a scope, so you can see when the primary current flattens out; when the coil has charged as much as it can.

[forcefed86]

I know approximately when the coil dwell peaks from scope testing on youtube videos.

As far as the spark duration goes.... I believe that’s calculated from the amount of time between individual coil firings per revolution of the crank? So as posted above they say mathematically a v8 4 stroke with COP will fire 1 coil ever 2.5ms at 6000RPM.

I was curious how they calculated that... don't believe a scope is needed for this? If they are saying it takes 15ms between sparks at 1000RPM and 2.5 at 6k... Would that put 7k at 2.14ms?

Just looking for ball park here. I believe 1ms is way too low.

[racingmini_mtl]

Spark duration is not an actually commanded thing but simply a time between successive dwell periods. The real spark duration is created by the ignition coil and the other ignition components and not under the ECU control. So 1ms is fine.

Jean

[billr]

A four-cylinder engine with COP has two crank revolutions to dwell and fire each coil, number of cylinders is irrelevant. That means 6000 rpm => 20msec for total of dwell/spark, and 7000 rpm => 17msec. There is far more time available for common dwell/spark than needed.

[forcefed86]

How is the number of cylinders/coils irrelevant. If I have twice as many cylinders and coils, wouldn't I'd have twice the time between each individual coil firing?

What is the point of having the 2 separate ignition settings in the MS software I suppose is my question. Why have spark duration and dwell? How will adjusting spark duration effect my spark?

Currently I'm running the square LS coils D581's. Over 6ms dwell there is little gain to be had. Currently the default settings are 4ms and 1 for spark duration. Seems like these settings aren't putting out optimum spark energy. I use the the dwell table so at cruise/idle I run much less dwell.

-Thanks!

[billr]

Note that I said "with COP". COP/CNP always means one coil/per cylinder; that 1:1 ratio is constant no matter how many cylinders there are. Maybe I made a mistake in assuming the single-tower coils you are talking about are used CNP. Do you intend to use one with a dizzy in a single-coil system? If so, yes, the number of cylinders matters a lot!

[forcefed86]

I honestly don’t know what I’m talking about here, so I appreciate the help. I’m sure I’m the one that wasn’t clear.

Now that I re-read the article, they are speaking about non-COP/CNP V8 setups requiring 2.5 MS at 6k RPM or so. This is what threw me off.

I’m running an LS based setup with an individual coil per cylinder, 8cyls. Trying to understand what settings I should use to get the most spark energy out of my current coil packs. They peak around 6ms of dwell I’m told. Does the spark duration field really even come into play on a CNP setup? Is there any difference if I enter a 1ms or 2ms in the spark duration field?

This is the article I am referencing.

http://www.megamanual.com/seq/coils.htm

[billr]

If they peak at 6 msec, then 6 (or a bit more) will give all the spark energy possible. However, even that 6 max may not be necessary and will cause greater heating of the coils.

Yes, my understanding is that the "spark duration" setting is only meaningful when there is insufficient time for the dwell/spark combo specified. The MS will "rob" time from one or the other (dwell or spark) according to the settings. With CNP (or even wasted) there is plenty of time so never a need for the MS to even consider that setting.

Abandon the Megamanual. It is obsolete and has not been kept updated or corrected.

[forcefed86]

If they peak at 6 msec, then 6 (or a bit more) will give all the spark energy possible. However, even that 6 max may not be necessary and will cause greater heating of the coils.

Yes, my understanding is that the "spark duration" setting is only meaningful when there is insufficient time for the dwell/spark combo specified. The MS will "rob" time from one or the other (dwell or spark) according to the settings. With CNP (or even wasted) there is plenty of time so never a need for the MS to even consider that setting.

Abandon the Megamanual. It is obsolete and has not been kept updated or corrected.

Will do thanks! I use the dwell table and only apply the higher dwell settings while the engine is in boost, so I wouldn't think I'd be over heating the coils. I'm at 4ms now I'll bump it to 5.5 in the upper RPM boosted cells and let it eat. I believe I read these max out completely at 8ms but see little improvement over 6.

Appreciate the help!

[Yves]

I've seen a GM dwell table for these, but I cannot find it anymore.

[old guy]

Her is the GM dwell table.