The keys to ignition

Engine ignition systems are a pet project of mine.  I will admit that I am somewhat obsessive about neatness and order in all things…especially ignition wiring.  Now I am talking here purely about the esthetics of ignition wiring.  I have a firm belief that part of the beauty of a hot rod motor is finding a way to route all the ignition wires in a neat and orderly fashion.  But first I suppose we should briefly cover the functionality of an ignition system.


The ignition system is responsible for taking the meager twelve volts that powers most of the electrical components in your car and transforming it into a hair-raising ten thousand volts necessary to jump across the gap of a spark plug and so wonderfully ignite the burning fury contained within your engine.  So how does it do this?  It does it with a transformer of course; or a coil if you are dead set on using the “proper” automotive terminology.  There are in most cases several other very important components contributing to the wonder that is a properly functioning ignition system, but in our discussion we are only going to cover the basics.  On almost all vehicles manufactured before 1970, the ignition systems consisted of a coil used to increase the voltage from the battery, a set of mechanical points which regulated the timing of the voltage delivery, and a distributor and rotor which directed the voltage to the proper spark plug at the proper moment.  All in all it was a fairly straightforward system, but one which required the fine skills of a Swiss watchmaker if it went awry.  In later years, manufacturers removed the mechanical points and replaced them with much more reliable electronic equivalent.  General motors integrated the coil and the distributor cap into one single unit, but overall, the functionality of the ignition system never changed.


Unfortunately there is too much variety in ignition systems to get into too much more detail, but the basic theories are as follows.  The more spark the better.  On most mechanical points type of ignition systems, increasing the spark is not an option.  Installing a larger coil and increasing the spark plug gaps will work for a short time, but will soon burn up your points.  If you can upgrade your distributor to a newer style that eliminates the mechanical points, do so.  This is one upgrade that is well worth the money.  An electronic distributor can save you untold amounts of time that would otherwise be spent cursing over the delicate art of adjusting mechanical points.  As for purchasing aftermarket ignition parts, it is most often unnecessary and any power increases will be barely noticeable.  As with many other speed components, they only contribute to horsepower increases if the engine is constantly running at high rpm or if you have a fairly high compression engine.


Here is a secret that a lot of auto parts representatives will wish I hadn’t told you.  Spark plugs are mostly the same.  There I said it, it’s out there.  There is simply not that much science that can possibly affect how well a spark plug functions.  Let me explain.  From a scientific standpoint, the only factor that affects a spark jumping across a gap is the width of the gap.  Some would argue that if one of the surfaces had a non-conducting coating, the spark would have a tougher time jumping across the gap, and that would be true.  But why would a spark plug company manufacture a spark plug that had anything less than an utterly conductive surface?   So here is the bottom line:  As long as the gap of a spark plug is set properly, that spark plug will work just as well as one that has platinum, chromium, titanium halide fluorescent bipolar nanotechnology.  In fact, as a spark plug wears out, the electrodes will become rounded and may become fouled with oil or soot.  As the electrode surfaces become less flat, there is less surface area for the spark to jump to, therefore the spark plug becomes less effective.  Replacing cheaper spark plugs more often is a much better solution than purchasing more expensive plugs and trying to use them longer.  But at any rate, from the perspective of one brand new spark plug being better than the next, it is simply, scientifically unlikey.  Several years ago a company introduced a product called the splitfire.  It was a spark plug that had a forked electrode which was supposed to allow the spark to protrude farther into the combustion chamber.  I would just like to point something out.  When lightning strikes the earth, where does it usually strike?  The highest point right?  The point on the earth that is closest to the sky.  The shortest distance.   A spark plug is no different.  The spark wants to jump the shortest distance possible.  What does it matter that the electrode of a spark plug is forked?  As if the electricity is going to jump between the forks of the electrode and miss both of them completely and shoot out into the combustion chamber?  Not possible, the spark is going to jump to the nearest part of the electrode, just like any other spark plug, except this plug has a forked electrode, so it has less surface area, so it basically wears out faster.  One theory that might hold some merit is that the fork in the electrode allows for better exposure of the spark to the combustion target.   This sounds a little far fetched does it not?  There is a great deal of science that goes into maximizing combustion, but most performance benefits will be a result of the size, shape, and flow characteristics of the combustion chamber.  The ignition or spark plays a crucial, but largely black or white role.  The spark is either there at the appropriate time or not.


So now that we know all about spark plugs, we move to the missing link: the plug wires.  Plug wires are not unlike spark plugs in that they all pretty much function exactly the same when they are new.  The difference is that worn out plug wires can cause a significant amount of trouble.  Plug wires are typically worn out more by heat than by any other factor.  Oftentimes being located very close to the exhaust manifolds causes the protective and electrically insulating outer jacket of the plug wire to dry out and crack, allowing the high voltage spark current to arc to some grounded metal component other than the spark plug.  Herein lies the difference between normal plug wires and some high performance wires.  Some high performance wires boast a silicone outer jacket that is supposedly immune to extreme heat.  In my personal experience, I have learned that the secret to spark plug wires is what I mentioned at the very beginning of this section:  proper routing.  Plug wires should never be allowed to touch exhaust components.  Now I realize that some header designs do not allow for any other option, but my point is that having a plug wire contact an exhaust component should be avoided at all costs.  If you find that there is no way around having some minimal contact, it is absolutely necessary to purchase high performance plug wires that won’t melt immediately.  However, if you can avoid contact, do so.


The best way to organize your ignition wire set is to buy a universal setoff plug wires and cut them to fit perfectly.  I have never once purchased a premade set of spark plug wires that fit properly.  There is always one or two that have so much slack you could make a lasso with them.  Taking the time to cut a custom set will not only allow you to route all the wires neatly but will ensure that you have the necessary excess to keep the wires safely away from any exhaust.  Unfortunately, you may have to purchase beg or borrow a crimping tool to install the ends onto your custom made plug wires.  Try you local parts store, often they will rent or loan tools.


One last note:  Worn out plug wires can be an aggravating and hard to diagnose problem.  I once spent weeks going from mechanic to mechanic trying to get my carburetor tuned properly only to discover that one of my plug wires was arcing out on the header.  If you suspect that one of your plug wires is hooped, or your engine is running rough, here is a trick to find the problem.  First of all, wear gloves and try to use an electrically insulated tool to manipulate spark plug wires.  While the engine is running, one at a time , remove each plug wire from its respective spark plug.  As you do so, you will notice the rhythm of the engine change.  Ie.  The cylinder that you have removed the spark from will be missing.   If you remove one of the plug wires and there is no difference, then that cylinder was not firing before you removed the wire.  Check this wire and spark plug and you may well have found your problem.


Let’s summarize this section with a list:


  • High performance spark plugs and wires will not significantly increase the power or overall performance of a stock engine.  In general, increasing the performance of an ignition system means increasing the distance or length of a spark.   This is accomplished by increasing the gap in the spark plugs.  The larger the gap in the spark plugs, the larger the coil you will need to facilitate the spark jumping across that gap.  In high performance (high compression) engines, having a strong stable spark will ensure that you are getting the maximum benefit from all the other speed components that are working together in an engine.
  • Faulty ignition systems can cause an endless number of frustrating symptoms in your engine.  Expensive spark plugs and plug wires will not increase the power of your motor.  However, fouled plugs, faulty plug wires, and worn or improperly adjusted mechanical point systems will cause missing and rough running.  If there is an electronic upgrade available for the mechanical points in your vehicle, it is well worth the money.  Check and replace your spark plugs often with affordable replacements instead of replacing them infrequently with expensive plugs.
  • Neatly routing the plug wires on your engine goes a long way for the esthetic appeal of your engine compartment.  The easiest way of doing this is to buy universal plug wires and cut them to length.  You can often rent or borrow the crimping tool needed to make plug wires at your local auto parts store.