Ignition Leads

"Thanks for reading my guide to performance ignition leads"

What is a HT lead or Ignition lead?

High tension or ignition leads connect each spark plug to the distributor or ignition coil.

They transmit the voltage to where it needs to be so if it's in bad condition the spark will be intermittent causing a misfire.

They have very thick outer coatings which is heat resistant and a very good insulator.

Why are they called High tension?

Tension is an age old phrase for Voltage, and high tension would indicate a very high voltage.

As the spark needs to jump an air gap you can appreciate just how high this voltage is.

Ignition leads carry the voltage to the plugs, they won't make the spark stronger or weaker but a bad lead can cause a misfire.

In older cars the HT ignition leads took the high voltage from the coil to the spark plug, this was very high voltage so could cause interference on the car radio, electrics.

Modern cars have a coilpack per spark plug so the leads are not strickly high tensions, they just carry the 12V charge to the coilpack where it is stepped up to be able to jump an air gap and create a spark.

This has resulted in smaller lighter leads.

No longer really called a high tension lead, so people refer to them as ignition leads, spark plug cables and even spark plug wires.

The outer casing is made from silicone, or rubber or some similar compound, it must keep out moisture, allow the lead to bend and flex and avoid any risk of the current arcing out.

You'll notice that each end has a rubber boot to keep out moisture, this also helps to maintain a good contact and insulate the internal wire.

Are high performance leads worth it?

They look nice but a lead is just a piece of coated copper wire so there is little performance benefit to adding them.

Often a performance core size will be as large as 8.5 mm whereas a street tuned car will probably get away with 7 or 8 mm core sizes.

That said they are usually better made, will last longer and ensure the sparks are equal.

When you measure resistance voltage and current flow you may see improvements with higher quality leads but I don't think this makes one scrap of difference to an engine, even a high performance one.

It's similar to the people that bang on about the important of oxygen free high grade speaker cable, where most people will not appreciate there is any discernible difference.

If you get interference from the electrical system then it's probably worth seeing if a high performance ignition lead will help improve this.

I read with some interest about a set of leads with build in tech that amplifies the voltage and leads to a stronger spark.

It turned out to just have a high resistance which shortened the spark duration, and the last thing you want is a shorter duration. The spark may have been bigger but not necessarily better.

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