Spark Plug info and part numbers

[jimmyjames]

I'll revise this later today but wanted to get this info back up. (as of right now it is incomplete)
Sorry, have to jam off to work.

Part numbers and what they mean:

NGK plugs:
NGK-IZFR6K11 = stock A3
NGK-IFR7G-11KS = stock A2 (1 step colder A3)
NGK-BKR7EIX-11 = stock A2 (1 step colder A3)
NGK-BKR7EIX = stock A2 (1 step colder A3)
NGK-BKR8EIX = 1 step colder A2 (2 steps colder A3)
NGK-BKR9EIX = 2 steps colder A2 (3 steps colder A3)

Denso Plugs:
IK20 = stock A3
IK22 = stock A2 (1 step colder A3)
IK24 = 1 step colder A2 (2 steps colder A3)

Example: NGK-IFR7G-11KS
I = Iridium type
F = 14mm dia., 19mm reach, 16mm hex
R = Resistor type plug
7 = Heat rating
G = Fine wire, nickel alloy center electrode
11 = 1.1mm (0.44") wide gap
KS = still checking

NGK heat rating goes from 2-11 (2 = hottest, 11 = coldest)
(See here for guide: http://www.ngksparkplugs.com/docs/te...tnumberkey.pdf )

Denso heat range number is the 20, 22, 24 (hottest to coldest)

Useful info
--------------------
Spark plugs are one of the most misunderstood components of an engine. Numerous questions have surfaced over the years, leaving many people confused.

This guide is designed to assist the technician, hobbyist, or race mechanics in understanding, using, and troubleshooting spark plugs. The information contained in this guide applies to all types of internal combustion engines.

Spark plugs are the "window" into the engine , and can be used as a valuable diagnostic tool. Like a patient's thermometer, the spark plug displays symptoms and conditions of the engine. The experienced tuner can analyze these symptoms to track down the root cause of many problems, or determine air/fuel ratios.

SPARK PLUG BASICS:
The spark plug has two primary functions:

* Ignite air/fuel mixture
* Transfer heat from the combustion chamber

Spark plugs carry electrical energy and turn fuel into working energy. A sufficient amount of voltage must be supplied by the ignition system to spark across the spark plug's gap. This is called "Electrical Performance."

The temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called "Thermal Performance", and is determined by the heat range selected.

It's important to remember spark plugs do not create heat, they only remove heat. The spark plug works as a heat exchanger
by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engine's cooling
system. The heat range is defined as a plug's ability to dissipate heat.

The rate of heat transfer is determined by:

* The insulator nose length
* Gas volume around the insulator nose
* The materials/construction of the center electrode and porcelain insulator

A spark plug's heat range has no relationship to the actual voltage transferred through the spark plug. Rather, the heat range is a measure of the spark plug's ability to remove heat from the combustion chamber. The heat range measurement is determined by several factors; the length of the ceramic center insulator nose and its' ability to absorb and transfer combustion heat, the material composition of the insulator and center electrode material.

Heat rating and heat flow path of Spark Plugs


The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C.

Tip Temperature and Firing End Appearance



The firing end appearance also depends on the spark plugs tip temperature. There are three basic diagnostic criteria for spark plugs: good, fouled and overheated. The borderline between the fouling and optimum operating regions (450° C ) is called the spark plug self-cleaning temperature. The temperature at this point is where the accumulated carbon and combustion deposits are burned off.

Keep in mind the insulator nose length is a determining factor in the heat range of a spark plug, the longer the insulator nose, the less heat is absorbed, and the further the heat must travel into the cylinder head water jackets. This means the plug has a higher internal temperature, and is said to be a hot plug. A hot spark plug maintains a higher internal operating temperature to burn off oil and carbon deposits, and has no relationship to spark quality or intensity.

Conversely, a cold spark plug has a shorter insulator nose and absorbs more combustion chamber heat. This heat travels a shorter distance, and allows the plug to operate at a lower internal temperature. A colder heat range is necessary when the engine is modified for performance, subjected to heavy loads, or is run at a high rpm for a significant period of time. Colder spark plugs remove heat quicker, reducing the chance of pre-ignition/detonation. Failure to use a cooler heat range in a modified application can lead to spark plug failure and severe engine damage.

Below is a list of external influences on a spark plug's operating temperature. The following symptoms or conditions may have an effect on the actual temperature of the spark plug. The spark plug cannot create these conditions, but it must be able to cope with the levels of heat...if not, the performance will suffer and engine damage can occur.

Air/Fuel Mixtures seriously affect engine performance and spark plug operating temperatures.

* Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor driveability
* Lean air/fuel mixtures cause plug tip and cylinder temperature to increase, resulting in pre-ignition, detonation, and possibly serious spark plug and engine damage
* It is important to read spark plugs many times during the tuning process to achieve the optimum air/ fuel mixture

Higher Compression Ratios/Forced Induction will elevate spark plug tip and in-cylinder temperatures

* Compression can be increased by performing any one of the following modifications:

a) reducing combustion chamber volume (i.e.: domed pistons, smaller chamber heads, mill ing heads, etc.)

b) adding forced induction (Nitrous, Turbocharging or Supercharging)

c) camshaft change
* As compression increases, a colder heat range plug, higher fuel octane, and careful attention to ignition timing and air/fuel ratios are necessary. Failure to select a colder spark plug can lead to spark plug/engine damage

Advancing Ignition Timing

* Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-100° C

Engine Speed and Load

* Increases in firing-end temperature are proportional to engine speed and load. When traveling at a consistent high rate of speed, or carrying/pushing very heavy loads, a colder heat range spark plug should be installed

Ambient Air Temperature

* As air temperature falls, air density/air volume becomes greater, resulting in leaner air/fuel mixtures.
* This creates higher cylinder pressures/temperatures and causes an increase in the spark plug's tip temperature. So, fuel delivery should be increased.
* As temperature increases, air density decreases, as does intake volume, fuel delivery should be decreased

Humidity

* As humidity increases, air intake volume decreases
* Result is lower combustion pressures and temperatures, causing a decrease in the spark plug's temperature and a reduction in available power.
* Air/fuel mixture should be leaner, depending upon ambient temperature.

Barometric Pressure/Altitude

* Also affects the spark plug's tip temperature
* The higher the altitude, the lower cylinder pressure becomes. As the cylinder temperature decreases, so does the plugs tip temperature
* Many mechanics attempt to "chase" tuning by changing spark plug heat ranges
* The real answer is to adjust air/fuel mixtures by rejetting in an effort to put more air back into the engine

Types of Abnormal Combustion

Pre-ignition

* Defined as: ignition of the air/fuel mixture before the pre-set ignition timing mark
* Caused by hot spots in the combustion chamber...can be caused
(or amplified) by over advanced timing, too hot a spark plug, low octane fuel, lean air/fuel mixture, too high compression, or insufficient engine cooling
* A change to a higher octane fuel, a colder plug, richer fuel mixture,
or lower compression may be in order
* You may also need to retard ignition timing, and check vehicle's cooling system
* Pre-ignition usually leads to detonation; pre-ignition an detonation are two separate events

Detonation

* The spark plug's worst enemy! (Besides fouling)
* Can break insulators or break off ground electrodes
* Pre-ignition most often leads to detonation
* Plug tip temperatures can spike to over 3000°F during the combustion process (in a racing engine)
* Most frequently caused by hot spots in the combustion chamber.
Hot spots will allow the air/fuel mixture to pre-ignite. As the piston is being forced upward by mechanical action of the connecting rod, the pre-ignited explosion will try to force the piston downward. If the piston can't go up (because of the force of the premature explosion) and it can't go down (because of the upward mo-tion of the connecting rod), the piston will rattle from side to side. The resulting shock wave causes an audible pinging sound. This is detonation.
* Most of the damage than an engine sustains when "detonating" is from excessive heat
* The spark plug is damaged by both the elevated temperatures and the accompanying shock wave, or concussion

Misfires

* A spark plug is said to have misfired when enough voltage has not been delivered to light off all fuel present in the combustion chamber at the proper moment of the power stroke (a few degrees before top dead center)
* A spark plug can deliver a weak spark (or no spark at all) for a variety of reasons...defective coil, too much compression with incorrect
plug gap, dry fouled or wet fouled spark plugs, insufficient ignition timing, etc.
* Slight misfires can cause a loss of performance for obvious reasons (if fuel is not lit, no energy is be-ing created)
* Severe misfires will cause poor fuel economy, poor driveability, and can lead to engine damage

Fouling

* Will occur when spark plug tip temperature is insufficient to burn off carbon, fuel, oil or other deposits
* Will cause spark to leach to metal shell...no spark across plug gap will cause a misfire
* Wet-fouled spark plugs must be changed...spark plugs will not fire
* Dry-fouled spark plugs can sometimes be cleaned by bringing engine up to operating temperature
* Before changing fouled spark plugs, be sure to eliminate root
cause of fouling

[jimmyjames]

Being able to "read" a spark plug can be a valuable tuning aid. By examining the insulator firing nose color, an experienced engine tuner can determine a great deal about the engine's overall operating condition.

In general, a light tan/gray color tells you that the spark plug is operating at optimum temperature and that the engine is in good condition. Dark coloring, such as heavy black wet or dry deposits can indicate an overly-rich condition, too cold a heat range spark plug, a possible vacuum leak, low compression, overly retarded timing or too large a plug gap.

If the deposits are wet, it can be an indication of a breached head gasket, poor oil control from ring or valvetrain problems or an extremely rich condition - depending on the nature of the liquid present at the firing tip.

Signs of fouling or excessive heat must be traced quickly to prevent further deterioration of performance and possible engine damage.

Normal Condition

An engine's condition can be judged by the appearance of the spark plug's firing end. If the firing end of a spark plug is brown or light gray, the condition can be judged to be good and the spark plug is functioning optimally.

Dry and Wet Fouling

Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon.

Overheating

When a spark plug overheats, deposits that have accumulated on the insulator tip melt and give the insulator tip a glazed or glossy appearance.

Deposits

The accumulation of deposits on the firing end is influenced by oil leakage, fuel quality and the engine's operating duration.

Lead Fouling

Lead fouling usually appears as yellowish brown deposits on the insulator nose. This can not be detected by a resitsance tester at room temperature. Lead compounds combine at different temperatures. Those formed at 370-470°C (700-790°F) having the greatest influence on lead resistance.

Breakage

Breakage is usually caused by thermal expansion and thermal shock due to sudden heating or cooling.

Normal Life

A worn spark plug not only wastes fuel but also strains the whole ignition system because the expanded gap (due to erosion) requires higher voltages. Normal rates of gap growth are as follows:
Four Stroke Engines: 0.01~0.02 mm/1,000 km (0.00063~0.000126 inches/1,000 miles)
Two Stroke Engines: 0.02~0.04 mm/1,000 km (0.000126~0.00252 inches/1,000 miles)

Abnormal Erosion

Abnormal electrode erosion is caused by the effects of corrosion, oxidation and reaction with lead - all resulting in abnormal gap growth.

Melting

Melting is caused by overheating. Mostly, the electrode surface is rather lustrous and uneven. The melting point of nickel alloy is 1,200~1,300°C (2,200~2,400°F).

Erosion, Corrosion and Oxidation

The material of the electrodes has oxidized, and when the oxidation is heavy it will be green on the surface. The surface of the electrodes are also fretted and rough.

Lead Erosion

Lead erosion is caused by lead compounds in the gasoline which react chemically with the material of the electrodes (nickel alloy) as high temperatures; crystal of nickel alloy fall off because of the lead compounds permeating and seperating the grain boundary of the nickel alloy. Typical lead erosion causes the surface of the ground electrode to become thinner, and the tip of the electrode looks as if it has been chipped.