Spark Plug Stuff

Codes for NGK Bosch and Champion

From Stuart King 12 April 2003:

NGK BP6ES, Bosch W7DC and Champion N9Y have same "heat value".

NGK BP7ES, Bosch W6DC and Champion N8Y are colder plugs.

NGK BP5ES, Bosch W8DC and Champion N10Y are hotter plugs.

link: http://www.ngkspark.com.au/spark_plug_cross_ref_chart_bosch_W5A_Y6DC.htm

Turbocharged engines

"In my ERA 1293cc engine I'm running NGK BPR6E plugs which is the standard plug for all post 1990 1275+ minis. Never had cause to try anything else. Previous owner had some 5ES's in when I got her and they melted with a few weeks."

Gaps

If you use one of those spark tester things you'll quite happily get 1" sparks on a 12V coil. This is at atmospheric pressure in air. Highly compressed petrol air mix is more difficult to arc through and hence a gap of greater than 1mm will soot up and misfire.

Temperatures

The "temperature" rating (eg: hotter/colder plug) is the plug tip temperature, not the conditions the plug is used in. A hotter plug is one which has LESS heat transfer (longer nose) meaning that when used in a normal engine the tip glows hotter giving a cleaner burn with less sooting up / oil contamination. A colder plug is the opposite and is usually used by the racers. This has a short nose and the heat generated by high compression is dissipated away easily to the head. Run one of these plugs on a normal street engine and it may suffer from blackening leading to eventual misfires.

I have found Champion plugs to be "cold" (sooty) compared to NGK/Bosch.