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Spark Plug Design
Every year the range of NGK spark plugs grows to accommodate the ever increasing demands of modern engines. Spark plug design must take into consideration many features of an engine including physical dimensions, combustion chamber shape, cooling abilities, fuel and ignition systems.
Spark plugs play a vital role in producing the maximum power from an engine whilst keeping fuel consumption and emissions to a minimum.
Choosing the correct spark plug type will help a vehicle manufacturer meet legislated emission targets and assists the motorist in getting the best from his engine.

Increases in the size and the requirement to improve the cooling of the inlet and exhaust valves have meant that the space available for the spark plug is severely restricted on some cylinder heads.
A change in spark plug design, possibly the adoption of a taper seat and extended reach (threaded portion) or even the use of a smaller diameter is often the answer. Some engines require the use of two spark plugs per cylinder and again due to space restrictions these might be of of different sizes.

Changes in fuelling systems and the fuel itself have meant some special features being adopted at the 'firing end' of the spark plug. Extra projected types push the spark position into the heart of the combustion chamber to promote better combustion of the fuel/air mixture, which is weaker than ever in an effort to improve economy. Modern engines manufacturers often require increased spark gaps to allow a longer spark duration, which again aids more efficient combustion.

To Combat the 'cold fouling' effect that can occur in some engines using unleaded fuels specially arranged ground electrodes are sometimes used. These can force the spark to discharge across the insulator and thus burn away any built up carbon that could cause poor starting or misfires. It is not uncommon to find two, three or four ground electrode arrangements in new vehicles. The use of precious metals on the tips of the spark plug electrodes is not uncommon especially on higher performance cars. Whilst these spark plugs do have increased service life they are often specified because of their superior ignition qualities.

NGK's engineering departments work very closely with the engine and vehicle manufacturers to produce the ideal spark plug type for each application. Any change in production is expensive for a manufacturer and therefore new spark plug types are only produced where necessary. NGK employ the very latest production technology to ensure that every aspect is catered for - performance, economy and value.

Heat Range and Heat Dissipation
Spark plugs do not produce heat in the combustion chamber. One of the functions of the spark plug is to dissipate some of the heat produced during combustion. This is mostly transferred into the cylinder head. The 'Heat Range' indicates the measure of the spark plug's ability to do this. A 'hot' spark plug is designed to maintain a sufficiently high temperature at the insulator nose to burn off carbon and oil deposits. A 'cold' spark plug is designed to allow a faster transfer of heat to the cylinder thus preventing overheating and premature failure.

The heat range selection is obviously a complex task with many factors to take into account. NGK engineers therefore make specific recommendations for each engine and the use to which it is put.

Wide Heat Range
A wide range spark plug is more flexible and performs equally well in a hot or cold engine under stop and go city driving or fast motorway cruising. Engines that tend to run hot need cold type plugs. Those that run cold demand a hotter type. The specific plug for any engine is determined by the plug's heat range. That is the minimum and maximum temperatures between which the plug will offer optimum performance.

The heat range of NGK Spark Plugs is wider than ordinary plugs therefore they are suitable for both high speed and low speed driving. Compared with conventional plugs of the same pre-ignition rating they have more resistance to fouling. Compared to ordinary plugs with equal anti-fouling resistance, NGK Spark Plugs have a higher pre-ignition rating.

NGK's Heart of Copper

Copper wire used in place of the iron core in conventional plugs is the secret of NGK's Wide Heat Range. Copper's superior heat conductivity dissipates heat quicker. It cools the electrode tip and insulator tip which prevents hot spots that could cause pre-igniton. Increased heat resistance does not affect fouling resistance, which is primarily determined by the insulator nose length. The longer the nose, the more susceptible it is to heat and the more free from fouling. By raising the pre-ignition rating with the high conduction copper and leaving the insulator nose long, NGK produces the Wide Range Plug. One that meets the broad thermal requirements of engines under high and low RPM conditions

Firing End Appearance

  • Overheating
    The insulator is white and sometimes blistered. If the insulator is over 870 degrees C pre-ignition may occur. Engine power will be reduced and the piston may be damaged
  • Causes
  • Over advanced ignition timing
  • Too lean a fuel mixture
  • Blocked injectors
  • Insufficient cooling
  • Excessive deposits in the combustion chamber
  • Good condition
    The insulator is brown or light grey
  • Even if the spark plug is used in ideal conditions, deposits will still accumulate. Regular inspection and replacement is advisable.
  • Fouling
    Carbon accumulates on the insulator nose forming a leakage path to earth. The engine misfires resulting in poor starting and acceleration. Particularly common with unleaded fuel
  • Causes
  • Too rich a fuel mixture
  • Excessive use of choke
  • Prolonged slow speed driving or idling
  • Blocked air filter
  • Spark plug heat range too cold

NGK Spark Plug Types

Wide Gap Types
e.g. BPR5ES-13

Good ignitability due to large spark plug gap
These plugs are mainly used to reduce emissions along with high output coils.
They should not be used on vehicles where the spark gap is specified as o.8mm as misfires may occur

Projected Types
e.g. BCRE527Y

1)To promote stable combustion the
firing end is projected into the middle
of the combustion chamber.
ZFR6E-11 is an extended shell type,
this is useful against fouling.

2) These plugs should only be used
where specified to avoid the piston
hitting the spark plug.

3 Ground electrode types
e.g. BCP6ET

1) Used by VW/Audi
2) These plugs have
longer service life

Double Platinum Types
e.g. BKR5EP-11

Platinum tips on the electrodes
provides good durability
PTR5A-10 for the
Ford Zetec engine

Semi Surface Types
e.g. BKR5EKU

1)Used by VW/Audi
2)Exceptional anti-fouling
3)Protects the catalyst

Supplementary Gap Types
e.g. BUR6ET

Spark discharge at the
supplementary gap burns away
the carbon on he insulator tip
to suppress a decline
of insulation resistance.
The small clearance between
the insulator and supplementary
gap reduces carbon accumulation
on the rest of the insulator by
preventing combustion gas
reaching this area of the insulator

Intermittent Gap Types
e.g. BKR6EK

Spark discharge at intermittent
gaps burn away the carbon on
the insulatorto suppress a
decline of insulation resistance

ISO Types
e.g. BKR6E-11

1)The insulator length of
'BK' type is 2.5mm shorter
than the BCP types
2)BK and BCP types are
not interchangable

NOTE: BKR6E-11 is V-grooved

V-Grooved Types
e.g. BKR6E

1)Improved cold starting
2)Enhances engine performance
3)More complete conbustion
4)Better exhaust emissions
5)Ideal for use with unleaded fuel

NGK copper cored V-grooved
sparkplugs have all the benefits
you would expect from the leaders
in copper core technology.
The unique V-grooved centre
electrode requires less voltage to
produce a better quality spark

OE Iridium Types
e.g. IZFR6B

1)Centre electrode with iridium tip
proven high performance
and high reliability
2)New iridium material ensures superior
anti-oxidation and anti corrosion
3)Iridium enables a very fine centre
electrode which reduces the electric
discharge voltage
4)Superior ignition efficiency
produces stable spark and enhances acceleration and power
5)New metal shell plating has
superior anti-corrosion properties
at high temperatures.

Resistor Types
e.g. BPR5ES
Uses a monolithic resistor to prevent
interference from electrical noise.

1)Prevents interference on car
radios, TVs and mobile phones
2)Expands the range of
communication equipment
3)Protects the cars electronic
management systems.

VX Types
e.g. BP7EVX

1)Centre electrode diameter is
only 1.0mm giving good ignitability.
2)Low required voltage due
to small centre electrode
3)Centre electrode made of



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