Resistor or Non-Resistor plugs with Points Distributor

[mtnjag]

(OK, OK, first lets get past this. i know, just enjoy the sweet sounds of the XK eng and don’t worry about music. Sorry, I enjoy some music on those long drives. :)

Running the original DMBZ6A dist with points. Solid copper wires and Non-resistor plugs. Thread in connectors to cap with the copper disks, only available cap i can find for this dist. Lucas Sport coil from late 80s with few miles on it.

I have a remote amp with RCA cables carrying the signal to it from a hidden Blue tooth head. I am getting ignition static with the recommended non-resistor plugs. No static with standard resistor plugs with 5K Ohm resistance.
I am told resistor plugs with this level of resistance is not desirable with points.

I have compromised and have installed a NGK Plug Cap, nice little piece, with only 1k Ohm resistance.
This alone eliminates the static.

Is this level of resistance still a problem?
Do i go wider on points gap?
Or?

Not looking for comments on audio system problems, looking for effect on engine performance issues.

Thanks for your comments and advice.
Thanks.

[cactusman]

Resistance won't affect the points at all. Really you should not be running a non suppressed HT system....as you have found it does not improve your in car sound system and there is a small risk of it sending a neighbouring modern car into electronic melt down!

[mtnjag]

Hmmm. The well regarded rebuilder of the distributor and pretty uniform recommendations i see on standard points distributor systems recommend solid core wires with non-resistor plugs.

Extraneous interference, yes.

(I will note that the orig Champion plastic plug boots were 5K Ohms resistance.)

[cactusman]

Solid core wires are fine...in fact with acorn screw terminals on the cap you cannot use carbon leads. Rules may be different where you live but in the UK it is technically illegal to run a non suppressed HT system On a public road....using resistance plugs will not affect either the points or the spark but will improve your radio....

[mgcjag]

Hi Layne...points are on the low tension side of the coil i dont understand how a HT suppression lead is going to affect it. .......whats the source of your information or is it just someones opinion......Steve

[cactusman]

My thoughts Steve.....

[mtnjag]

Source of info is the well regarded distributor rebuilder and numerous articles on the subject from seemingly reliable sources-Hagerty, collector car mags, (as well as the "experts" on the internet which I am not giving weight to.)

So with 5K Ohm resistor plugs there is no effect on voltage at the plug gap?


Nope, in California no restrictions on a wide open copper circuit coil to plugs. No vehicle inspections any longer either. If you can nail it together, put wheels on it, appropriate lights, a horn, and seatbelts you can license it and drive it on the roads. And we are probably the most restrictive state.

[cactusman]

Afraid they are talking nonsense. No significant current flows until the plug strikes the arc and once struck the HT voltage falls dramatically anyway due to the impedance.of the HT coil. The resistance stops dramatic changes of current with time dv/dt and resonance which which cause severe RFI. It is why almost all plugs incorporate resistance. As Steve says the resistance can have no effect on the life time of the points as they are on the primary. My 3.8 runs copper leads.and resistance caps (rather than plugs). You may well have resistance caps anyway....try measuring between the cap connection to the plug and the screw thread into the lead....you may well find it is 5 or even 10 k.

[mtnjag]

"No significant current flows until the plug strikes the arc and once struck the HT voltage falls dramatically anyway due to the impedance.of the HT coil."

Ok, I have a basic understanding of the timing of the spark not being effected, which is one of the points made in the articles.

But I may have not understood, is this addressing whether or not there is a reduction in Voltage at the plug's electrodes effecting the arc due to the resistance of the plug or cap?




Hope this pic comes through.
The NGK caps are 1K Ohm. They make 0,1, and 5K ohm caps.
Very nice quality pieces. Also have a waterproof boot from the hard cap to the plug, not shown.

[mgcjag]

Hi Layne " I am told resistor plugs with this level of resistance is not desirable with points"

This the above us what i was questioning......as re suppressed leads or resistor plugs yes the resistance will affect the spark....but i have never heard that resistive leads/plugs are not desirable with points....and have no idea why this could be....Steve

[cactusman]

I would recommend a search of the internet as there is an enormous amount of information on how the ignition system works.....the spark plug manufacturers themselves for example. The wiring may be simple but the operation is not. I do NOT claim to be an expert....but In extremely simple terms the points close and a current flows in the primary of the coil and builds up a magnetic field. At the appropriate time the points open. The primary current falls towards zero and the magnetic field starts to collapse. The collapse induces a very high voltage in the secondary and a spark is generated in the plug. The condenser across the points prevents an arc across the points which would severely reduce the energy delivered to the plug and also massively upset the timing of the now weakened spark/arc..which is why open circuit condenser failure leads to very rough running.

The ionized gas at the spark has a low resistance and an arc forms as the energy stored in the magnetic field is dissipated in the arc. The arc lights the fuel which burns. During the spark/arc phase the voltages and currents in the secondary vary enormously over fractions of a second and can generate large RFI fields. The resistance is there to limit the arc current and this the RFI . While the arc current may be lower it is still sufficient to generate enough heat to light the fuel air mix and because the system is dumping a preset amount of energy from the coil into the arc it may actually mean the arc lasts fractionally longer as the dissipation rate is lower. And yes some energy is lost in the resistance but lots more is lost in the coil. Added to all this the ignition system has to initiate the arc at the right time such that the burn happens at the right time in the cylinder cycle...advance. To further complicate things as engine speed rises the points are closed for less and less time meaning less time for the coil to 'charge' ready for the next ignition. This is especially problematic in high revving multicylinder engines....indeed some V12 engines have two six point caps and two coils to mitigate the issue....modern engines now have individual coils per plug....and the mechanical points with their condenser and inevitable wear are replaced by electronic switching....the ignition system is a marvel and not as simple as it seems....and the secondary voltage should be negative at the plug electrode so the centre electrode emits elections rather than the other one.....just to add one more thing...

[mtnjag]

Good description, thanks. I have done quite a bit of searching the net and some of the same info is presented as in your post. Without understanding fully what the heck you are saying it seems as though:

-Yes, the amount of voltage supplied to the electrode is effected by the resistance but not enough to matter.
-Is that correct?

-Also noted on the net is another issue you mention which is the amount of sparking resistance effects the timing and burn rate of the fuel.
-The point made on the net is -Lower spark level results in later and longer burn cycle effecting timing and possible detonation.

Steve-The supposed reason non-resistor wires and plugs are not recommended for points ign is that modern ignitions put out a much higher voltage spark that overcomes the resistance in the circuit Take a look at output voltage in a MSD or perhaps a Megajolt system compared to a stock coil.

Me, I don't know, just seeking answers.

[cactusman]

Incidentally my Aug 1961 E type spares book lists C16979 ' Terminal for sparking plug leads (incorporating suppressor)' and C17456 'Terminal for sparking plug leads...for export only' suggesting that even in 1961 UK cars had suppressed caps...export cars did not. If you have suppressed caps you don't need resistance plugs

[mtnjag]

Interesting on the caps. This car came from the original owner and had resistor Champion caps but no radio was ever installed. I measured the caps and they ranged from about 5K to more than 11K. They're in the originals box.

Yep, just running the 1K ohm resistor NGK caps for now with non-resistor plugs.

I got some repro Champion caps at one point but they were all over the place in resistance including one with no continuity so I tossed them. I think they had left the resistor out as I recall.

Thanks

[cactusman]

And from bitter experience not all reproduction suppressed caps are equal. I bought two sets from fleabay....with both sets at least one failed open circuit within 100 miles....cause....the copies used metal film resistors. They are not suitable for use in the high voltage world of ignition systems. The originals (I dissected a broken one) used carbon for slugs....very inaccurate but very robust.

The last set I got from SNG after getting an assurance that theirs did not use metal film resistors. So far and a few thousand miles so good.

Easy way to tell apart without dissecting. Get your set of six and measure their resistances. If they are metal film they will all be almost exactly 5000 (or 10000 ohms)...I mean within a percent of nominal. so if they are all say 4998 ohms put them in the rubbish immediately. If they are carbon slugs they will be far more variable....probably within 5 or 10 % or more of nominal....these are the ones you want....accuracy is not important.

[mtnjag]

I gave up on the repros.
I found these NGK while looking around on this subject I like 'em. They are not Champion Logo but they definitely have a vintage look to them very similar to the origs and I believe NGK is going to have a reliable quality product, whatever resistor they use. These are commonly used in off road racing, snowmobiles, wave runners, and outdoor equip. There are some post on the site that reference them I believe.