A few quick lessons on ignition theory :Dwell time:
- 1ms very weak spark
- 2ms usable spark in SOME applications with decent modern coils (maybe yours)
- 3ms usually enough, coils stays cold, spark is ok
- 4ms enough for most, coils may get warm, spark is good
- 5ms max, full dwell to saturation, coils will get warm, spark is best
- >5ms, part of the time is spent purely as a DC load, this solely heats the coil and does not benefit spark energy at all
Obviously this depends on both the coil design and how how they are switched with some approaches producing full saturation in a shorter time, and with a higher energy level, than others.Spark duration:
Formula to show time available per cylinder:
- We'll assume that its 1ms long for point of discussion.
Time per cylinder = 1000 ms / ((((X RPM / 2 RPEC) / 60 s) * Y cyls) / Z coils)
Where RPEC = Revs Per Engine Cycle
At 7000 RPM with 6 cyls and 1 coil = 2.85ms
If you subtract a spark time of 1ms then dwell = 1.85ms
which is WAY
too short. Even assuming the spark is instant, it's still too short really...So, if you want boost and a dizzy, wheres your effective good ignition zone?
With a 6 cylinder at 7k RPM you can have:
- 3ms dwell to 5krpm
- 4ms dwell to 4krpm
- 5ms dwell to 3350rpm
Now, go wasted spark and things are looking a lot better:
You are instantly OK.
- 7k 4.7ms dwell
- 7500 4.33ms dwell
- 8000 4ms dwell
COP just means you allow the coils to stay totally cool working for 1/4 the time or so.
For example, my 4 cylinder with 4 coils : 16ms per engine cycle to do as required, 5ms dwell leaves 11ms for the spark and a nice coffee break :-)
That is why distributors are no good in a high performance application. There are many other reasons such as long leads, caps, rotors, firewall issues with RWD setups.
Here is the formula loaded into google calc ready for you to play with for your application.http://www.google.com/search?hl=en&safe ... tnG=Search
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