Does anybody run aftermarket ignition box with stock coils???

[mk3ukr]

This subject was discussed recently, but there was no answer to this question:
Does anybody run aftermarket ignition box with stock coils???
I have AEM CDI, when I try to run it I get huge arcing under the stock coils. My option is either to buy new stock coils ($350) or set of aftermarket coils for $150-180.
I prefer to stay with stock configuration because AEM CDI had some issues, it burned on few people cars. I don't want to be stranded somewhere far away from home. With stock coils I can return to stock ignition by inserting bypass plug into the harness
Thanks
Vladimir, 89T

 

[Mr. Y]

Hi, Vladimir!
Just now, I'm thinking of standalone ECU, I can afford only Megasquirt&Spark with my money..... ;-) And I researched ignition topic a bit...

So, if you are going to keep stock wasted spark, you need 3-chanel ignitor (if AEM has 3 not multiplexed outputs). If your AEM can manage ignitor like stock ECU does (3 multiplexed lines), why not to use stock ignitor? I thinks, It will be most rational way If you aren't going to COP yet...

PS:in theory you can also just use three one-chanel ignitors (from LADA, for example ;-) to run stock coils, but some problems with tach signal may occur ;-)

 

[mk3ukr]

Hello Denis,
I suggest not to worry about mk3 ignition system and spend money elsewhere. I purchased my CDI 1.5 years ago when I was injecting pure water with my Aquamist. It seemed to me I had high rpm miss @1.5bar boost with water. Of course I was wrong. Now, when I found good source of methanol and inject 50/50 mix it runs much smoother. Read this
http://www.thesupraforums.com/showthread.php?p=5945#post5945

Vladimir, 89T

 

[figgie]

umm the stock coils are for inductive based ignition. I doubt they were ever meant to work with CDI.

But iwth that out of the way. You should be able to run the GM DIS coils instead of the stock 7m-GTE coils. Should being the key word here

 

[mk3ukr]

umm the stock coils are for inductive based ignition. I doubt they were ever meant to work with CDI.

But iwth that out of the way. You should be able to run the GM DIS coils instead of the stock 7m-GTE coils. Should being the key word here

Figgie, do you mean GM DIS coils will work with CDI? They also based on inductive ignition.
I want to find coils which work equally well with AEM CDI and stock ignition in case I fry my CDI. Most performance DIS coils have very low primary winding resistance, much lower than stock coils 0.3-0.5 ohm
Vladimir, 89T

 

[IJ.]

I'm using a set of MSD Dis Coils with the Dis4's.

MSD do a twin post motorcycle coil and had suggested it for the Dis4 if I was going to btch/waste fire them.

 

[cjsupra90]

pretty much all coils are inductive and the ignition system has nothing to do with being inductive. For the most part, a coil is a coil when it comes to the type of ingition system that it is use with. Inductive systems are cheaper to build and work well for Mass production OEM's to keep cost down. I have used MSD CDI's on many cars with stock coils and have never had a problem with them due to the CDI unit. Chances are are that due to age and constant heat cycling the coils has just developed cracks in them. It is a bad design idea that Toyota and many others have done by putting the coils on top of the motor as in factory turbo set up. one the coil itself generates a lot of heat, toped with the radiant heat coming off of the motor and last but not least, putting a plastic cover on top of it to make it more visually appeling acts as an insulator to trap more heat in. this is pretty much the only thing that I dont like about COP units, but thermo plastices have come a long way in the past few years.

You have to be careful when using performance coils on stock Ign. systems. the lower primary resistance can fry a stock ignitor. That is why some performance coils state to not be used without a CDI box of sort. This lower resistance will cause a higher amperage draw on the Ign. drive transistor within the ignitor box. If this amperage is higher then what it can handle then you will burn it up. This is why coil A which is intended for OEM manufacture A might be different then coil B and manufacture B. This is also why old points type systems and early electronic type systems used ballast resistors.

All that a coil is is a step up transformer and steps up the voltage based on the winding ratio between the primary and secondary windings. This is what makes it an inductive device. a voltage is supplied and the ignitor supplies a ground path which generates a magnetic field in the coil. When the ground path is removed, a voltage spike is induced into the primary winding (usually around 300 to 400 volts) and the magnetic field drops which then the voltage is induced into the secondary winding and depending on the winding ratio the voltage is multiplied. All that a CDI box does is ups the primary voltage and the coil then multiplies the voltage from there.

 

[IJ.]

Good post Chris!

The MSD Dis Coils are wound for 400v primary and while they do fire after bypassing the CDI they're lethargic and would be Limp mode only with 12v in.

 

[mk3ukr]

Thanks for the info, that is exactly what I wanted to know.
Vladimir, 89T

 

[Nick M]

Actually plastic has an R value of about zero. It insulates nothing. I think it is zero anyway.

 

[cjsupra90]

well to an extent, you are right and in the case of the coil cover, yeah its not a very good insulator, I guess that I should have stated that it slows the heat escape rate down. The hole point is that it makes it look better, but it's not a good idea or design idea. I have tested it with a K type thremocouple on a Fluke Meter and although I dont remember the exact temps plus they will very on a number of other factors, I did see about a 20*F differance with and without the cover. Now in the event that we are talking about thermo plastics, they are very good insulator. That and there higher temperature use capability and ease of manufactering is why they are used for many parts on modern cars.