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Ignition Systems

Spark Plugs

How would you like to be shut in a chamber with temperatures of up to 3000°C, splashed with petrol and given a 30,000 volt electric shock 25 times a second, and be subjected to pressures 50 times greater than normal atmosphere? No? - well that’s what your spark plugs are subjected to! So if you want peak performance from your engine, make sure you fit suitable plugs.

Three main points to consider are;

  1. All modern engines are now fitted with resistor type plugs and you are advised to stick with this type. The high energy bursts from plugs can cause interference to ICE, EFi and engine management systems if resistor plugs are not fitted.
  2. Plug heat range - many plug manufacturers produce a competition range which are usually harder or colder than the standard fitment. For mild road tuning it is best to stick with the factory recommended item but colder plugs will be necessary for seriously modified engines.
  3. Electrode gap - unless there is a known benefit for doing otherwise, we advise setting the gaps as recommended. Some uprated ignition systems can generate a spark across a wider gap which may improve combustion. However, on high boost turbo engines a large plug gap may result in the spark being blown out and for these engines a reduction in the gap is usually specified e.g. Cosworth types.

Ignition Coils

Ballast and Non-Ballast Ignition Systems

Contact breaker (points) type ignition systems, as fitted to most Ford models up to around 1980 (although it lasted up to 1987 for the Capri), can have either a ballast fitted in the wiring loom or not.

What is a ballast?

Quite simply, it is a resistor that has the purpose of reducing the voltage to the coil.

Why do some ignition systems have a ballast fitted where others do not?

Originally, all ignition systems did not have a ballast fitted which meant that the ignition system used a 12v coil with a 12v feed from the battery via the ignition switch. Such a system works fine when an engine is running, but problems can occur when starting the engine. The starter motor draws a huge current from the battery leaving less energy to create a spark across the spark plugs. The result is a weaker than normal spark which is not ideal for starting an engine. This problem is worsened by colder temperatures and/or a worn starter motor which will draw even more energy for starting and leave even less energy for sparking. To overcome such a problem, ignition systems were changed to run a lower voltage coil (usually 9v), and these coils could still give the same output as the original 12v coils. In order to run such a coil, the 12v ignition feed runs through a ballast, reducing it to 9v at the coil. To assist starting, a 12v feed (usually from the starter) bypasses the 9v ignition feed, giving the 9v coil a 12v feed. The result is a better than normal spark which is ideal for starting, particularly on cold damp mornings. As soon as the engine has started, the 12v feed is cut and the coil will run on the 9v ignition feed.

How do I know which ignition system is fitted?

Ballast ignition systems were introduced in around 1970. Virtually all Ford models from this date should have a ballast fitted. To find out for sure, use a multimeter to check the voltage on the positive wire of the coil with the ignition on. Around 9v means you have a ballast, around 12v means you don’t.

Which coil should I use with a ballast ignition system?

Without modifying your ignition system, you can use any standard ballast coil or we offer performance ballast coils from Bosch (red coil 0221119030) or Intermotor (gold coil DLB110). Using a non-ballasted coil would mean that you are running a 12v coil on a 9v feed, resulting in a weak spark. You can however use such coils provided you remove the ballast resister.

Which coil should I use with a non-ballast ignition system?

Use any standard non-ballast coil, or we offer performance non-ballast coils from Bosch (blue coil 0221119027) or Intermotor (gold coil DLB105). Do not use a ballast coil. Although you may gain a performance advantage using such coils, failure will be imminent!

Ignition Leads

The sensitive electronic systems on modern cars need protecting from outside interference, so just like the plugs above, the leads must be able to suppress the high voltage bursts flowing through them. Good quality carbon cored 8mm silicone leads are quite adequate for most mild tune applications but the carbon core will degrade and performance will drop off over a period of time (typically 2-3 years). High performance silicone leads (up to 10mm) with a ferromagnetic/glass fibre core will out-perform and outlast their carbon cored cousins.


Pre engine management cars rely on mechanical distributors to adjust the ignition timing through the rev range. Most highly modified high revving engines will require a different advance curve to the standard distributor to achieve peak power. The usual requirement is for more ignition advance at low engine speeds and slightly less total advance which would typically occur between 2,500 - 3,000 rpm. DIY alterations to standard distributors can be quite successful but also time consuming - you rarely get it right first time. Also, if it is badly worn it should be replaced, in which case you might as well buy one already modified for you!

Electronic Ignition Systems

Up until the early eighties most European cars still had the now redundant contact points system, with all its inherent problems (burnt contacts, points bounce at high rpm, etc.). Early Electronic conversion systems were either very unreliable, expensive or both. But as technology progressed and performance improved, all major car manufacturers had their engines factory fitted with various contactless ignition systems. Engine efficiency can be greatly improved by fitting an electronic ignition kit to an existing points type distributor. Once fitted these systems are maintenance free and can operate at engine speeds far in excess of the very best contact points system. The two main types of electronic ignition are inductive and constant energy, the latter being the type most commonly used by car manufacturers.