Ignition Leads

[Graham Barker]

I have acquired a Powerspark electronic distributor that I am going to try on my Ruby. Powerspark recommend using either silicon or resistive leads instead of copper leads. 
Do members have experience with these leads that would suggest that one of these types of leads is better than the other for use in an Austin 7?

[John Cornforth]

Hi Graham

Silicone is the type of rubber often used for the outer insulation. It's very durable but is irrelevant to this question.

Resistive cored leads of some kind are sometimes required to reduce the level of radio frequency energy that would otherwise upset the electronics. This used to be achieved by a core of graphite loaded nylon "string" that would eventually break down and cause trouble. The typical resistance was a few thousand ohms per foot.

More modern "inductive" cable uses a fine spiral of wire wound over a ferrite core, with a resistance of a few hundred ohms per foot. It's much more reliable.

You might find that copper cored cable in conjunction with resistor type spark plugs will achieve the same result. Many plugs can be cross referenced to a resistor type equivalent.

[Ruairidh Dunford]

Just use the normal copper cored leads and plugs, Graham, they will be absolutely fine.

The two most important things to promote longevity in these units are:

- ensuring you have no loose connections anywhere in the system, a spark will fry the unit very quickly indeed.

- using a coil which has at least 2.4 ohms of protection, anything less will erode the unit. It is often easier to find a 12v coil with this, or more, and they will work fine on 6v.

[Graham Barker]

Thanks, John and Ruairidh for your comments. I am considering using a resistor to bring the coil resistance (currently 1.1 ohm) up to the value that Ruairigh suggests. Would that work?
Incidently, I have just had an email from Powerspark saying that because my system is 6volts, their distributor will work fine with my coil resistance of 1.1 ohm.  Does using a higher resistance mean that the distributor electronics will operate with less heat and therefore last longer?
Do you think that use of resistive leads is to prevent interference with the distributor electronics or is it to prevent interference with other devices?
Regards 
Graham

[Ruairidh Dunford]

Only one way to find out, Graham.

[Fencepost]

I am using standard copper core leads and plugs with the accuspark unit and have had no problems. I always believed that the need for resistive core leads or plugs was to lessen radio interference. No radio in my austin!

[John Cornforth]

Just to add some history

Starting in the 1950's, ignition suppression became a legal requirement (not retrospective) and was intended to stop excessive radio frequency interference from ignition systems upsetting other people's radios and televisions. If you had your own car radio, that would be more susceptible so a variety of components were sold to "top up" the supression.

Roll forward a few decades and cars began to be fitted with more and more onboard electronics. As these progressively became more complex and sensitive, they became more and more susceptible to being upset by radio interference, so the need for good suppression continued. A simple electronic ignition like the Powerspark is at the more robust end of the electronics scale and is unlikely to be affected, whereas something like an electronic tachometer is more likely to be upset by an unsuppressed system. Anything with embedded software like a modern ECU would probably never function without suppression in place.

So the Powerspark may or may not work OK, but there is no significant downside to adding suppression

[Howard Wright]

Hi

To follow up John’s excellent comments. I have electrictronic tachometers in the Special and the van. A very nice period looking one from Willie MacKenzie in the former and a cheap eBay purchase in the latter. Neither will work without suppressed cables. I think there are several different electronic ignition systems some more complex than others. I have a Distributor Doctor modified DJ4 (manual distributor) in the van which seems more robust than a Powerspark DK4 copy which I found difficult to set up and now resides on a shelf.

Powerspark carbon leads at least look relatively period being black and having no lettering!

Cheers

Howard

[Chris Garner]

I know zilch about electronics, but the Willie supplied electronic tachometer works fine in my GE Super Sports rep. with the bog standard copper plug leads.

[Malcolm Parker]

The above posts confirm my view that an original ignition set-up, even if slightly worn, is more likely to get you home.  I have always carried a spare Lucas DK4 and used traditional copper cored HT leads.  There have been times when I have had to strip and rebuild the distributor at the road side, usually due to a bad electrical contact, but I have never been left stranded by faulty ignition.   I suppose the truth is that I don't understand modern electrical systems.  With the original system if you accidentally short the electrics you will get a spark whereas with the modern electronic gizmos they will be destroyed.
Regarding electronic tachometers, the Willie MacKenzie one on the Ulster worked fine with conventional copper plug leads and no suppression.
Looking back, interference was one of the many joys of listening to the radio in my childhood!