Torque is one of the most critical aspects of spark plug installation. Torque directly affects the spark plugs' ability to transfer heat out of the combustion chamber. A spark plug that is under-torqued will not be fully seated on the cylinder head, hence heat transfer will be slowed. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. Serious engine damage is not far behind.
An over-torqued spark plug can suffer from severe stress to the Metal Shell which in turn can distort the spark plug's inner gas seals or even cause a hairline fracture to the spark plug's insulator...in either case, heat transfer can again be slowed and the above mentioned conditions can occur.
The spark plug holes must always be cleaned prior to installation, otherwise you may be torquing against dirt or debris and the spark plug may actually end up under-torqued, even though your torque wrench says otherwise. Of course, you should only install spark plugs in a cool engine, because metal expands when it's hot and installation may prove difficult. Proper torque specs for both aluminum and cast iron cylinder heads are listed below.
Since the gap size has a direct affect on the spark plug's tip temperature and on the voltage necessary to ionize (light) the air/fuel mixture, careful attention is required. While it is a popular misconception that plugs are pre-gapped from the factory, the fact remains that the gap must be adjusted for the vehicle that the spark plug is intended for. Those with modified engines must remember that a modified engine with higher compression or forced induction will typically require a smaller gap settings (to ensure ignitability in these denser air/fuel mixtures). As a rule, the more power you are making, the smaller the gap you will need.
A spark plug's voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture maximizes burn efficiency. It is for this reason that most racers add high power ignition systems. The added power allows them to open the gap yet still provide a strong spark.
With this mind, many think the larger the gap the better. In fact, some aftermarket ignition systems boast that their systems can tolerate gaps that are extreme. Be wary of such claims. In most cases, the largest gap you can run may still be smaller than you think.
Indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction.
However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine. While most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve.
In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output. For a 500hp engine, you'd be lucky to get 5hp. While there are exceptions, the bottom line is that without a dyno, gauging success will be difficult.
Let's make this really simple: when you need your engine to run a little cooler, run a colder plug. When you need your engine to run a little hotter, run a hotter spark plug. However, NGK strongly cautions people that going to a hotter spark plug can sometimes mask a serious symptom of another problem that can lead to engine damage. Be very careful with heat ranges. Seek professional guidance if you are unsure.
With modified engines (those engines that have increased their compression) more heat is a by-product of the added power that normally comes with increased compression. In short, select one heat range colder for every 75-100 hp you add, or when you significantly raise compression. Also remember to retard the timing a little and to increase fuel enrichment and octane. These tips are critical when adding forced induction (turbos, superchargers or nitrous kits), and failure to address ALL of these areas will virtually guarantee engine damage.
An engine that has poor oil control can sometimes mask the symptom temporarily by running a slightly hotter spark plug. While this is a "Band-Aid" approach, it is one of the only examples of when and why one would select a hotter spark plug.
Be cautious! In reality, most "racing" spark plugs are just colder heat ranges of the street versions of the spark plug. They don't provide any more voltage to the spark plug tip! Their internal construction is no different (in NGK's case, as all of our spark plugs must conform to the same level of quality controls) than most standard spark plugs.
There are some exceptions, though. Extremely high compression cars or those running exotic fuels will have different spark plug requirements and hence NGK makes spark plugs that are well-suited for these requirements. They are classified as "specialized spark plugs for racing applications". Some are built with precious metal alloy tips for greater durability and the ability to fire in denser or leaner air/fuel mixtures. However, installing the same spark plugs Kenny Bernstein uses in his 300+ mph Top Fuel car (running Nitromethane at a 2:1 air/fuel ratio and over 20:1 dynamic compression) in your basically stock Honda Civic (running 15:1 a/f ratios with roughly 9.5:1 compression) will do nothing for you! In fact, since Kenny's plugs are fully 4 heat ranges colder, they'd foul out in your Honda in just a few minutes.
NGK as a company tries to stay clear of saying that a racing spark plug (or ANY spark plug) will give you large gains in horsepower. While certain spark plugs are better suited to certain applications (and we're happy to counsel you in the right direction) we try to tell people that are looking to "screw in" some cheap horsepower that, in most cases, spark plugs are not the answer.
To be blunt, when experienced tuners build race motors, they select their spark plugs for different reasons: to remove heat more efficiently, provide sufficient spark to completely light all the air/fuel mixture, to survive the added stresses placed upon a high performance engine's spark plugs, and to achieve optimum piston-to-plug clearance.
Some of these "specialized racing plugs" are made with precious metal alloy center/ground electrodes or fine wire tips or retracted-nose insulators. Again, these features do not necessarily mean that the spark plug will allow the engine to make more power, but these features are what allow the spark plug to survive in these tortuous conditions. Most racers know screwing in a new set of spark plugs will not magically "unlock" hidden horsepower.
Many of the more popular aftermarket ignition systems are of the capacitive discharge type. They store voltage, or accumulate it, until a point at which a trigger signal allows release of this more powerful spark. Companies like Mallory, MSD, Crane and Accel, to name a few, offer such systems.
They affect spark plugs in that they allow the gaps to be opened up to take advantage of the increased capacity. The theory is that the larger and the more intense the spark you are able to present to the air/fuel mixture, the more likely you will be to burn more fuel, and hence the more power you will make.
We encourage the use of such systems, but only on modified or older non-computer controlled vehicles.
In reality, computer controlled vehicles do such a good job of lighting off the air/fuel mixture (as evidenced by the ultra-low emissions), added ignition capacity would do little to burn more fuel since the stock configuration is doing such a good job. Older non-computer controlled vehicles or those that have been modified with higher compression or boosted (nitrous, turbo, supercharged) engines can certainly take advantage of a more powerful ignition system.
Applying anti-seize to the threads of spark plugs that have a metal plating allows the installer to mistakenly over-tighten the spark plug in the cylinder head; This stretches and fatigues the threads ofthe spark plugs, causing a much higher probability that the plug will break during installation or in somecases upon removal.
Image shows an example of 10mm thread spark plug broken during installation due to the use of anti-seizeleadingto over-tightening. (Note that plug gasket has been completely compressed, anti-seize can be seenon threads, and the break is in the direction of tightening).
For spark plugs with special metal plating simply do not use anti-seize on initialInstallation; All NGK Spark Plugs are manufactured with a special trivalent Zinc-chromate shell plating that is designed to prevent both corrosion and seizure to the cylinder head; Thus eliminating the need for any thread compounds or lubricants.
NGK recommends only using spark plugs with metal plating on all aluminum head applications to prevent damage to the head and plug. Metal shell plating acts as a “lubricant” which breaks away from the main body of the spark plug during removal, preventing damage to the spark plug and or threads in the cylinder head.
All spark plugs that have a blackened or dull appearance on the metal body offer no protection against seizing or bonding to the cylinder head and so it is with these spark plugs that anti-seize would be required. A spark plug that has a shiny silver appearance on the metal body usually indicates that the plug is manufactured with metal shell plating and therefore will not require anti-seize.
If you’re a gear head your well aware you have to pay to play. There’s many ways to build horsepower however one of the easiest and least expensive ways to build horsepower is to install a nitrous system. The term laughing gas is fitting for a product that provides sheer excitement on and off the track.
Nitrous Oxide was first discovered in 1793 by the English scientist and clergyman Joseph Priestley. Priestly first thought nitrous oxide could be used as a preservingagent to no avail. Soon it was discovered, that when inhaled, nitrous oxide made people laugh and giggle, hence the term laughing gas. For the next forty years nitrous oxide was used for entertainment purposes in traveling medicine shows and carnivals.
In the mid 1800’s it was discovered when nitrous oxide was inhaled, the human body felt little pain. An experiment was performed in a dentist’s office to determine if nitrous oxide would provide pain relief during tooth extractions. The successful experiment introduced general anesthetic and is still used in dentist offices to this day.
During World War II nitrous oxide was introduced to boost power in aircraft engines. Since its introduction into the internal combustion engine, nitrous oxide has proven to be a cost effective means to build horsepower.
Nitrous Oxide is a colorless almost odorless gas containing two parts nitrogen and one part oxygen. When nitrous oxide is heated to approximately 570 °F the nitrogen and oxygen split. Since more oxygen is being injected into the combustion chamber more fuel can be injected enabling an engine to create more horsepower.
Another advantage occurs during the vaporization process. When Nitrous Oxide vaporizes it cools the intake air temperature, which in turn increases air density, providing more oxygen and higher compression.
Nitrous kits are available for EFI, Carbureted and Diesel applications. Many companies offer plate, direct port and nozzle type systems. Systems are available in single stage and two stage systems. If you’re considering a nitrous system we highly recommend contacting reputable nitrous companies in order to select the correct nitrous system for your application.
A wet nitrous system introduces a homogenous mixture of nitrous and atomized fuel into the intake air. Wet nitrous systems are safe provided you properly tune your vehicle and follow the instructions provided with your system. Wet systems are recommended for naturally aspirated and forced induction applications.
A dry nitrous system injects nitrous directly into the intake runners or injector plate.
Dry systems are recommended for naturally aspirated engines and are not recommended for use in forced induction applications. These systems are simple to install and tune. Again it’s important to properly tune your vehicle and follow the instructions provided with your system.
So how does nitrous oxide affect thes park plug? More horsepower’s produced because we’re injecting more oxygen, fuel and air density is higher. All these factors create more heat. What do we do with the excess heat? To answer this question we must first understand how the spark plug works.
The spark plug has two functions; one is to ignite the air/fuel mixture and the other is to transfer heat from the combustion chamber. Spark Plug heat range is selected through a series of pre-ignition tests. Thermal couple spark plugs are used to record internal center electrode and ground electrode tip temperatures. Optimum firing end temperatures must fall between 500C ~ 800C. If the tip temperature falls below 450C the spark plug is considered to be in the fouling region. This means the tip temperature isn’t hot enough to burn off carbon deposits. If the tip temperature rise’s above 800C the spark plug tip temperatureis too hot and the spark plugis considered to be in the pre-ignition region. Pre-ignition is detrimental to an engine and can ultimately lead to spark plug failure and extensive engine damage.
A spark plug must dissipate heat generated in the combustion chamber. Insulator nose lengths determine heat rating if the insulator nose is long the spark plug is considered to be a hot type and if the insulator nose is short it’s considered to be a cold type Heat is transferred out of the combustion chamber through the spark plugs insulator into the cylinder head cooling passages.
A stock 1999 Honda Civic Si is pre-ignition tested at the factory and a heat range of six has been selected for the application based on the spark plugs tip temperature. This means the tip temperature falls within the 500°C ~ 800°C window and is hot enough to burn off carbon deposits and cool enough to prevent pre-ignition. If we use a stock heatrange of six and add a 125 hp shot of nitrous, the spark plugs firing end temperature will rise above 800°C. At thispoint the tip temperature is too hot and pre-ignition will occur, leading to spark plug failure and extensive engine damage. We must select a cooler spark plug with a shorter insulator nose so the correct amount of heat is transferred bringing the tip temperature within the 500°C ~ 800°C window.
Unfortunately spark plug manufacturers are unable to manufacture adjustable heat range spark plugs. NGK Spark Plugs recommends dropping one heat range for every 75 shot of nitrous. When using less than a 75 shot of nitrous on the street, one step cooler spark plugs should be sufficient provided air/fuel ratio and timing are adjusted properly. When two step cooler spark plugs are utilized on the street the tip temperature under normal operating conditions (without nitrous) may be too cold and possible spark plug fouling may occur. Fouling can lead spark plug insulator failure, drivability issues, loss of performance and poor starting.
When large amounts of nitrous are being used on the street we recommend switching spark plugs in and out. Use a hotter spark plug when running all motor and a cooler spark plug for nights you decide to run nitrous.
Racing applications follow the same guidelines.. Select a spark plug for your engine without nitrous and then select a spark plug for nitrous. For every 75 shot of nitrous drop one heat range. Race vehicles in most cases run enormous amounts of nitrous so it’s not uncommon to use extremely cool spark plugs. This can pose a problem when the race vehicle is driven to the starting line, pit area and idled for extended periods. Spark Plug fouling occurs rapidly in race vehicles leading to loss of power, misfiring, poor starting and spark plug failure. Again make sure you’ve adjusted air/fuel ratio and timing correctly.
It is highly recommend replacing spark plugs every round as a safety precaution.
Whether you own a street/strip car or an all out race car, nitrous is a cost effective way to build horsepower. Simple to install, nitrous has many benefits provided you follow the instructions and properly tune. Failure to tune your vehicle properly will guarantee spark plug failure and severe engine damage.