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Correct settings question for "Spark Duration", G+ Fury ECU


Pete_89t2

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I just wanted to confirm that I'm using the correct spark duration settings for my coils. The car is a single turbo S6 RX7 FD that is running AEM IGN1A smart coils in direct fire/COP mode. According to the coil's spec sheets that I downloaded from AEM (see attached), it lists an "Arc Duration" specification of 2.9mS (+/- 10%). Am I correct in thinking that "Arc Duration" is the same thing as "Spark Duration", and I should be plugging that 2.9mS value into my G+ Fury?

I'm somewhat confused, as the car seems to be running fine with its current setting of 2.0mS from its prior owner, and the Link help file for this parameter states typical values range from 0.5 to 1.0mS.

Thanks!

30-2853 High Output Inductive Smart Coil.pdf

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You are correct, spark duration and arc duration are the same thing.  

In your case this setting may only just start to come into play a high rpm. 

The spark duration setting usually only comes in to play when you have a distributor with single coil and more than 4 cylinders.  It is used to shorten the dwell at high RPM when there is not enough time to both charge the coil and spark for the full duration.

As an example think of a V8 with a distributor running at 6000RPM.  At 6000RPM one engine cycle (two crank revs) takes 20ms.  All 8 cylinders have to fire in that time.  Lets say your coil needs 2ms of dwell to charge and the spark lasts for 1.0ms.  You have to do that 8 times in those 2 revolutions, 8 x 3ms = 24ms - but wait - you only have 20ms to do that in?  The ECU cant do anything about the spark so if it knows how long the spark needs and there is not enough time then it can shorten the dwell to make everything fit into the time that is available.

A rotary in direct spark mode at 8000RPM will have 7.5ms of cycle time to charge and spark.  So if you have a spark duration of 2.9ms that leaves you with about 4.6ms for dwell.  You generally dont need much more than 3ms on those coils unless very high boost or Methanol.  

With it set at 2.0ms now is not a big problem because as you can see it is quite likely you are not running into cycle time issues anyway. 

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Thanks Adam, that's a great explanation and it answers what would have been my next question regarding dwell settings. Besides the fact that these coils don't need more than 3mS dwell in most situations, your math confirms the previous owner had his dwell settings set WAY too long, and backwards -- 7.0mS at the RPMs above 6K which clearly would not end well! Luckily for me the motor is new and still being broken in at under 4500 RPMs, so no fried coils or a blown motor.

I've updated the old dwell table per the attached file. For voltages above 13V, and RPMs below the 8K redline, I have dwell set at 3.0mS. I reduced that to 2.6~2.5mS for voltages above 14V and RPMs > 8K to protect the coil from overheating. At voltages 12V or less, and RPMs under 1K, I bumped up the dwell to 4.0mS. Thought there was to get a hotter spark during cranking/start up, and to help promote a smooth idle when the electrical loads on the system are high (e.g., lights, AC & e-fans operating)

Ignition Dwell Control (ms).lte

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