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To:            "diy_efi (postings)" <DIY_EFI at coulomb.eng.ohio-state.edu>
Cc:            
Subject:       Re: Q: dual ended ignition coil

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	VNM3043:  David Atchley at m2000@TFS_BLDG_6

Someone wrote:

> use a standard coil and make a Y splitter using some some glass epoxy
> board and some sutible studs and  insulate the thing with silicon
> rubber    all the dual coil is in my estimation is an standard hei coil
> with two outputs in parellel    " there's a schematic in my buicks
> chilton"

The "dual ended coil" is in fact different than the standard coil.  In the 
standard coil, one end of the secondary is common with the primary, and the 
other end goes to the distributor.  In the dual ended coil, both ends of the 
secondary are floating, and they each connect to a spark plug.  Both spark 
plugs are now in series with the secondary, and they fire at the same time. 
 The trick is to choose the cylinders so that one is on the exhaust stroke 
while the other is on the compression stroke.

Using a standard coil with two plugs in parallel will not work.  With both 
spark plugs in parallel, the plug with the least gap resistance will fire 
first, ionize the air, the resistance will drop significantly, and that plug 
will discharge all of the energy.  This will be the plug on the exhaust 
stroke (I think), since the hot exhaust gas will have a lower resistance 
than the compressed gasses on the compression stroke.

Bryan Zublin
bzublin at gi.com