I recently acquired a stock ZX14 with a scratched exhaust. I found a replacement on ebay. It was a good buy, and fit very well. I noticed the original exhaust had a part number stamped on it K528. Both the left and right canisters matched. The one I bought on ebay had the number K518 on it. Does anyone know what the number represents, and does anyone know if there is any functional difference between the two?

Those are country designation pipes.

Say K510 is USA
Say K520 is Asia
Say K530 is Canada and so forth. Not that we have the correct matching whatever codes. Where did that pipe come from? Technically, that is your answer without knowing the real K numbers... This is book spec designation. In other words, does it come with cat or is it open? You read the K numbers against the book and you have to remember that those letters/numbers are 6 years old. So, subtle changes are always happening to the 14. It may not show the old 06' numbers [in the book] as you have a 6 year span. You would need the other updated shop manual to follow the codes if they continue thru the years. This is how you might tell the year, what country, etc.

As far as the two being different? Look at the engine and how it fires off. It fires off 4-times, right? That one hot ball of gas, heading down two exits. You think one fast side or one slow side is going to make a squat of a difference? If both are matching clogged on both sides say, was that pipe now installed going to show a difference? What if it is one of the more [open] internal designs being a variable... Wink-Wink! No matter WOT, no harm no foul.

Thanks Hub. The pipe came to me (in N/W Washington State) from an ebay seller in Texas.

You got it, mind. It's not a Cali emissions so I'm pretty sure you have the generic USA. Unless we all year date ourselves to death, we could see all those K500 numbers. And what would it be good for? Someone down the road restores some 14 for some bike show. A judge knows the pipe numbers and scores your 100-Point bike down to a 99'er. Other than that, mix and match who cares.