By Jay Lloyds, UCR Member (from May 2017 Provinz page 38)
You may discard this article; some may take note, either way it is important for all of us to pay attention as to what goes into our high-performance cars. I also wish for you and your technician to discuss the reason he has decided on a specific set of sparks plugs for your engine and how he came to that logic. The following is written with the express knowledge that these notes are taken from my experiences, what has worked for me may not work for you.
Dating back to the start of mankind, someone, somehow discovered the first ever ignition source for fire. Whether it was a spark from a flint or heat by way of friction, little did they know their “flicker of life” would eventually be used in what we call the “car.” An amazing invention if you really think about it, something on wheels with a huge pump that works by combusting a highly flammable substance and then by way of a spark ignites the compressed particles, which converts ignition to energy and from there the importance of inertia. The first nuclear weapon used an ignition source to flash of the thermite/cordite charge that drove a piston at extreme speed into a mix of highly reactive material, giving us the first ever Atomic Bomb. So, do not disregard the importance of a little spark, it is the source for light and life, but unfortunately death.
Amazing really that these little units of spark assists us with going to work, heats our homes, helps us in war time, cooks our meals and even put man on the moon. A rocket motor like the ones used for the Apollo Space Program didn’t use any moving parts, all that was needed was a highly pressurized, highly flammable liquid propellant mixed with liquid oxygen and a spark to ignite the mix. NASA actually quotes these as “spark plugs”. They used a total of five F1 engines in the first stage to lift the Saturn V vehicle off the launch pad, reported by NASA to be equal to 175 million horse-power. This machine was the largest ever built for flight yet, without the mighty “spark” it could not go anywhere.
The development of the spark plug comes from very humble beginnings; many prototypes were tried but back in 1886 when Mr. Etienne Lenoir applied for the first patent on the improvements to an internal combustion engine he also built a type of spark plug for his application. Nicola Tesla also had patents on early ignition sources along with his study and development of electricity. These engineers/ scientists didn’t have computers and other equipment to help design and develop this new ignition source, they experimented with various ferrous metals that could be utilized for the central core while not forgetting to develop the outside casing. It had to be a single unit, controlled within itself. They discovered that Porcelain was ideal for the task, it was a great isolator and an insulator and allows pulses of spark through the central electrode without penetrating through the outer body, but they remained aware that a crack in the porcelain will seriously affect the performance of the spark plug and therefore poor performance from the engine. It was Mr. Gottlob Honold in 1902 that was first credited with the modern design of the spark unit, it just so happened he worked for the Robert Bosch Company.
An ignition coil or magneto is employed to charge the power behind the spark, when electric current leaves a highly-charged coil it enters the spark plug and travels through the central core to create a short-circuit type of event. When the dielectric strength is reached the tip of the plug becomes ionized and the compressed charge is enough to trigger the spark. Voltage ignition coils on earlier cars were charging from 15,000-25,000 volts but with fuels becoming more sophisticated and the engines internal compression rising it necessitated the development of coils that burn as high as 40,000-50,000 volts. For this reason, ignition systems are marked with “warning, high voltage” stickers, the ignition source is so charged that a shock from the system can be fatal. As fuels became more sophisticated so too did the spark-plug, making it all the more important for choosing the correct spark plug for a specific application.
Spark plug electrodes nowadays are made from an assortment of exotic materials with copper, chromium, nickel-iron, platinum, tungsten, iridium, silver and even palladium giving the tuner a vast selection to choose from. Newer technology allows us to use very exotic materials, making the units very reliable but quite expensive. The outside insulator utilizes anything from the basic porcelain to the sintered alumina type. The sintered kind is an extremely hard ceramic that boasts a long life along with the ability to withstand extreme temperatures; it is this cover where you will find the manufacturers brand etched into the ceramic. The entire insulator is glazed to help seal the porosity of the raw ceramic, an unglazed finish would be porous allowing for a myriad of issues including spark jump.
The biggest issue we are faced with today is choosing the right plug. The choice of plug decides the fuel you will use and vice versa. All fuels and oils have had to evolve due to the severe pollution effects they have on our atmosphere and our health, the use of lead has long been eliminated. This makes it quite challenging for the fuel/spark management system to work efficiently and the higher the demand on the engine the higher the energy is needed to flash off the mix. Therefore, a spark plug’s heat range is extremely important for all and every engine, regardless of the fuel type being used. One needs to be very careful with the selection of a plug and is heavily dependent on the type of driving you do and what fuels you use. For me it references like this: A high-performance engine which is higher in compression or air-charged by way of super or turbo charger would need a cooler plug that works very well at the top end of the engine rev range yet have good enough heat qualities to burn the fuel and clean the plug at the lower RPM. The opposite is true for the lower performing engines that sit in traffic all day every day and never see higher RPM’s near redline, under these conditions the engine would require a hotter spark plug. Most spark plugs and how they work depends mostly on the ability to burn-off the soot, carbon and oil left behind by every combustion event. If the plug is too hot at the higher end it self cleans very well but the overheat can melt the core which in turn overheats the porcelain which can break off and ruin your well-designed, very expensive motor. It also has a serious negative effect with the frightening possibility of detonation which is detrimental to any engine regardless of its make-up. If it is too cold then the combustion mix will not spark-off while driving around town and the plugs would eventually foul, which gives poor performance and an increased fuel consumption rate. Examining the porcelain near the electrode tip is one way to help determine if it is a cold or a hot plug, the thicker the porcelain the colder it is, and thinner is the opposite but this is a reference only as the make-up of the central core is also related to the heat range. Choosing to go with twin spark plugs makes it easier to determine what spark plugs will work, twin plug gives you a more reliable burn, more horsepower and better fuel economy but it is expensive. A spark plugs heat range has no negative effect on how hot the coolant or the oil temperatures will be.
An important fact often overlooked by technicians is the air gap from the tip of the electrode to the grounding post. All plugs from Bosch are pre-gapped though you should always check this with an appropriate feeler gauge. The gap itself should be adjusted to what the factory recommends but if you are looking for better performance or you are tracking your car and maybe using different fuels then experimenting with the gap can yield better performance. There are spark plugs with 2,3 or 4 posts, with these plugs it is not possible to set the gap and has been gapped at point of manufacturing.
We must consider two of the most important items in regards to matching a spark plug to an engine, horsepower and torque, they are very different and happen at different times, though they do cross-paths for a very brief time. In most cases horsepower starts from zero through the rev range with it normally dropping off around 1,000rpm below peak revs. With real torque its range starts in most cars at approximately 1,500-2,000rpm above idle and at full throttle it continues to climb to approximately 4-5,000rpms after which it mostly flatlines, unless you have a high revving GT3, equivalent or a high boost turbo motor. Now the plugs come in to play, 90% of all detonation begins at about 15% after the start of torque, it is at this time when the possibility of trouble begins. All detonation on all engines is a killer, a boosted engine it’s even worse, you can destroy a $100,000 turbocharged engine within 3 gear changes. Once the detonation starts the only way to stop it is to immediately get your foot off the throttle, but by then it could already be too late. Nearly all cases of detonation isn’t initiated by a colder plug, yet it is very possible a hotter plug may assist in the end of an engine, hence the caution.
Example, a 930 turbo motor has an idle timing of about 5-8 degrees before top dead center “TDC” with the angle widening as the revs rise. Its when the engine starts its torque curve that things can go terribly wrong, as the torque starts to climb the ignition has to dial-back the spark timing in order to avoid a problem. Once the torque is 60-70% through its travel the ignition control unit can start adding back timing all the way to the top so as by 6,000 or more you can increase the timing to 24-32 degrees advance, pending on what type of engine you have and again the fuels you use. The reason for this is simple and I will explain it simply as this… because the piston is travelling so fast that the ignition timing has to catch up to the engine rather than the engine catching up with timing, it is this catch-up event that can ruin your very expensive engine, I know this because I have seen good engines destroy themselves on a dynamometer, it’s what nightmares are made of.
Manufacturing got more sophisticated in the eighties and now these expensive engines have on-board computer systems monitoring the events of every engine cycle. Destruction of an engine in past years happened all too often, but thanks to the O2 sensor, a cylinder head temperature sensor and the all-important knock detector sensor engines now have a much better chance at survival. These computers can sense if the engine is using good fuel or bad fuel, high octane or low octane and can adjust themselves accordingly. But that said you still have to be aware of what goes into your car, this includes the gas you use. My thinking is this, Porsche’s built from 1999-2017 should always go with what Porsche recommended from new, anything older you can experiment with. I have built engines that are identical but used different spark plugs, this was mainly due to what the engine was going to be used for along with the different fuels it would consume. You may have to try a couple of different heat ranges to find the spark plug that works best for you and your engine. Race engines are in a category all by themselves but using the same guidelines you may have to run a few sets till the desired performance has been achieved, this can also be performed using a rolling road dyno.
We have to discuss a little about the art of inspecting the tip of the spark plug and you need to understand what to look for and what you are looking at. It’s easy yet difficult, as you need to understand fully what the deposits on the plug tip is telling you. The best way of reading a spark plug after being removed from the cylinder head is to look at the tip. The area to look at are the electrode, the center porcelain and the outer body that sits within the combustion chamber, I use a high definition magnifying glass with a light source. A light brownish discoloration of the tip at the block indicates proper operation; other conditions may indicate malfunction. For example, a sandblasted look to the tip of the spark plug could mean persistent, light detonation is occurring, any damage that is occurring to the tip of the spark plug will represent the same occurrence on the inside of the cylinder. If the plug looks oily, or it has many carbon deposits or runs a different colour than the rest then you most likely have some issues that need immediate attention. If the surface looks clean, a little dark and is not shiny with no oil deposits then most likely your engine is running well but a little rich, there is one more thing to consider during this inspection, the actual colour of the tip must be equal to that of all the other spark plugs on the remaining cylinders, if not then you may have an issue with the injectors, fuel pressures and or the engine itself. In the days when we had lead and other additives and better quality fuels the spark plug would always have a creamy hew to it, and sometimes almost white, off white. They were also much easier to read than what we see today, with the unleaded gas burning away and entering the catalytic converter the only colour you will see now is black and nothing more than black making it tough to dial in an engine.
When I was first getting into racing in the seventies an old trick that some of you may know is indexing. Indexing the plug means that by the use of various thickness sealing washers on the plug threaded body at the head we could determine where the ground tip would be and how deep the plug protruded into the combustion chamber. By indexing the spark plug we could determine if the spark was facing the combustion mix or turned away from it. Performing this was a drastic measure, but it gave us an edge. Nowadays I think this trick has long been forgotten.
Finally, a reminder: the tip of a spark plug sits in one of the Worlds harshest environments so the next time you start your car you can reflect on that and have some respect for the little units, for without these you ain’t going anywhere.