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Premium Member
11,898 Posts
29.00 vs 43.00 is quite a difference.

Over here, there are so many people who sell them and no one charges the same price. The online Kawasaki parts sellers have them for somewhere between 9.99-14.00 and that is for the EIA version.

That surprises me. It's been years since I bothered to check, but years ago Kawasaki had terrible pricing on those plugs. The bodywork was a lot cheaper, but the plugs were twice what they are now.

A Black 2019 N1K
466 Posts
This explanation involves some simple Maths, but if Maths gives you a headache, then jump to the last paragraph (**).

Let us assume that the engine of your typical 4-cylinder Toyota Camry, cruising down the highway at 100 kph, is turning over around 2,000 revs per minute (rpm). As the engine is a 4-stroke, this means that the ignition produces 1,000 sparks per minute.

Over 1 hour and 100 kms, that is 60,000 sparks for each spark plug.

Your typical N1K, doing 100 kph @ 4,5000 rpm is producing 2,250 sparks per minute or 135,000 sparks for each spark plug for the same 100 kms.

So the Camry has 60,000 sparks while the N1K has 135,000 sparks. You still with me ??

As spark plug tip wear is a function of the number of sparks, the plugs in the N1K will erode more than twice as fast as those in the Camry.

NGK state that their Laser Iridium plugs have a "typical life" of 100,000 kms. This does not mean that they stop working at 100,001 kms. Rather their performance drops off and they start "failing to fire" resulting in an increase in pollution due to un-burnt fuel, etc.

But the 100,000kms is in a car, so your "average" N1K, which produces more sparks per km, will have a "typical life" of only 46,000 kms.

Now, your "average" Camry driver very rarely hits the rev limiter, but your "average" N1K rider will often venture into the higher rev range.

More rpm = more sparks = quicker tip erosion = shorter plug life.

At 8,000 rpm, there are 4,000 sparks per minute, or 240,000 sparks per hour, resulting in a"typical life" of only 25,000 kms.

I would suggest that the engine of your "average" N1K spends most of it's time between 4,000 ~ 7,000 rpm, so a "typical life" of a spark plug in a N1K is probably somewhere between 25K & 46K, say 35,000 kms.

Of course, these numbers assume that NGK's "100,000 kms" life is not marketing hype. If it is, the "typical life" in a N1K is a lot shorter.

** IMHO, replacing the plugs every 12,000 kms (7,500 mi) as per the manual is probably an "over-kill" to meet EPA rules, but I will definitely replace them before they hit 35,000 kms (21,000 mi).
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