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Date: Sun, 01 May 2011 13:27:14 -0400
From: Ernest Christley <echristley@att.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Timing Question for Tracy
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Lehanover@aol.com wrote:

> Most engine builders don't bother with the split. It has time to work at 
> low speed where more mixture is forced into the cavity in front of the 
> plug, and then you get a flame thrower effect when it fires. Not the 
> case at speed, so it is for emissions for the most part. 
>  
> In boosted engines that split starts to look like a detonation event, so 
> again fire both at once.

I threw my back out again last week, and the drugs have my sleeping pattern all out of whack.  Last night, I spent 
another 6 hours researching what other people have done.  One guy reported that he started loosing performance with 2* 
of split at speed.  It was a boosted engine on a dyno.  The problem I have with the RX-7 forum is that they are all guys 
looking for ridiculous performance running street engines on a dyno.  You have to read between the lines on all of it. 
He didn't go any further than 2*, because of the performance drop off, but that fits perfectly with what you're saying 
about detonation.

I'm going to go with what I've got now, but I'm seriously reconsidering recasting the mount for the trailing VR sensor 
to take out split as a near future project.  There is more to fear from detonation that a little more low end emissions.

>  
> That problem firing a double ended coil is the gap size on the plugs. Us 
> plugs you can change the gap on, and set the gap at .010" to .015".
>  
> I used those even with an MSD and never had the problem. Remember the 
> rotor is hauling the mixture past the plugs like a freight train.
> AR2592 Autolite work fine. Same heat range as NGK -10s. But usually 
> $7.00 a box of 4 at Autozone. The open tip may get better cooling than 
> the NGKs

Ok, Lynn.  That deserves some type of reward for being a brain dead simple solution to the root cause of the problem. 
If you're not getting a spark because you've set up to much resistance to the current flow, cut back on the resistance.

I learned a bit more about this in the research last night.  You have a couple of very authoritative guys giving very 
scientific and clear explanations of why using a split coil won't work.  You have another set of guys going, "Really? 
I've been driving that setup for the past 6 months."   The differentiation seems to once again be boost.  So I'm 
confident that I can run the single coil set using the wasted spark on the trailing, and I can just swap out the plugs 
if it looks like I start missing when the engine is under load.

The ultimate goal, though, is to have two totally independent ignition sources.  The MegaSquirt guys have worked out the 
circuitry to run the stock coils or even COP.  The problem I have with that is that it puts ignition control back in the 
little homemade box.  I like the idea of having the two highly resilient, time-proven ignition systems that will keep 
right on clicking if my fancy little computer goes tits up.  I'll loose control of the advance, but I can be confident 
that the limp-home mode of 25* will drag me to crash site.

And that leads me to my next question.  Operationally, what would be the pros/cons of turning off the trailing during 
cruise flight?  Will it allow deposit to build up and ensure the plugs are fouled if I ever do REALLY need them?  Or is 
it just putting a needless load on my generator in order to dump an incremental amount of extra heat under the cowl?