From NGK's web page
                      6. Using "racing" spark plugs
                      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.
Knowing that go here to find the spark plug that fits your application.

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