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Discussion Starter · #1 ·
This is interesting read, thought I’d share.

The part on external shielding (as on 60’s BBC Corvette stainless braid) effectiveness is opposite of what I thought it was for.

I guess not everything in the “muscle car” time period was optimum.

I’m wondering if chrome metal ignition shielding on small block fiberglass cars, Avanti and Corvettes was doing any good. Maybe more of an eye appeal when hood was open than anything.
 

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Seems to devolve into an add for Magnecore. Not to say it doesn’t contain useful information that’s mostly correct.

Probably the biggest problem with distributor ignition systems is switching stability and coil impedance’s effects on that.

Points and modules have limits. They switch only so fast plus you can tie coil saturation time to this as well. As RPM goes up time to act goes down. If your a seeker of high RPM you need to look for parts that function beyond what the OEM’s use for commuter service. Lower coil impedance nets faster cycle time but need to be matched to the module as now the module is switching higher current so you can expect a stock module or an aftermarket that is designed around a high impedance coil load will not be happy for long. However, a mismatch of a low impedance module with a high impedance coil is functionally OK, your just not getting the spark the module could sustain with a low impedance coil in that combination.

CDI essentially shortens the coil current build up time by slamming the primary with higher electrical pressure (voltage). This results in a shorter discharge period which is likely to lead to to low RPM misfires going back to the cylinder pressure being low because of throttling the incoming air so with molecules of sir and fuel being fewer and further apart it is harder to set on fire. Thus the transistor circuit includes a timer to switch the coil on and off inside the global discharge period since electronic switching can be done so quickly. The multiple sparks adds spark time more like a straight inductive system but generally detween 2000 and 3000 RPM depending on component quality time for this game runs out. The CDI in pure form being rather opposite to inductive systems where the latter perform better in lower RPM ranges than high while the former does better in high RPM ranges than lower. Thus the crutch of low RPM multi strikes reduces lower rev misfires while retaining the high RPM performance capabilities of these systems. This leads back to getting squish/quench and swirl/tumble optimized while using tight chambers is important when building the engine. Without CDI high RPM ignition performance is a lot harder to attain. Certainly solid state individual cylinder timing by computer with coil on plug by cylinder eliminates the classic problem of getting coil situation time between discharges. On a distributor V8’s the coil has to recharge 4 times every crankshaft revolution where coil on plug recharges over two crankshaft revolutions.

Bogie
 

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Discussion Starter · #4 ·
I found the shielding information was most enlightening to me. Being that GM in the 60’s performance (Corvette) did just that with stainless braid shield wire and sheet metal ignition shielding in other applications. I was aware of the spark to the plugs as it passed along the wires “rode” the outside surfaces of the wire strands. This on the wire surface path would seem to me should warrant more discussion as smaller strand copper wire s/b a better choice. Not having any computer and radio turned off makes my requirements less EME and RFI sensitive. Also only being concerned with a street application, higher RPM (over 6 grand) is not a requirement so inductive ignition is fine.

As for the advertising plug with all the other shared information they presented, I can over look that. It’s not often that an ad holds my attention.
 
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