|I've tested most every type of
spark plug available. There are some "racing only" plugs
that go for over $40 each !!
The NGK CR9EK or NGK CR10EK are the only
ones I've ever seen make a power difference. They cost about $7.00
- $9.00 each. The gain is from 1 to 2 horsepower increase,
depending on the condition of the plugs you're replacing. That's a
huge money to power ratio!
The "9" or "10" number
refers to the heat range, which also doesn't matter. (it really
The "EK" refers to the fact that
they have dual electrodes. There isn't any advantage to having 2
electrodes. Think about it: You can't beat physics and get 2
sparks at one time. (That's the "Splitfire Theory")
Do They Work Better ??
One reason the CR9EK's or CR10EK's make more power is because they
take up more space in the combustion chamber, which increases the
compression ratio. The second reason is that the spark is
.040" / 1mm deeper into the combustion chamber. I think that
increases the burning efficiency at high speeds.
They work so well that Yamaha uses installs them in the R6 from
One word of warning: they have to be
replaced more often since the last thread of the plug extends into
the combustion chamber. This means that as the thread on the plug
gets loaded with carbon over time, it can damage the threads in
the head on the way back out. If you don't want to change your
plugs once a season, these aren't for you.