TuckerBag wrote:

So,.. Compression ratio = (124.8cc + 9.6cc) / 9.6cc = 14.0 : 1 (NOT 7.9 : 1 as stated by HRC ?? Maybe this is just a typo?)

Tucker,
7.9:1 compression ratio is according to how Japanese started measuring secondary compression a couple decades back,
also know as CCR ("corrected" compression ratio).

They do not use the displacement of the cylinder e.g 125cc for the nsr,
but they instead use the displacement of the cylinder just after the piston has blocked the exhaust port.

This might be a bit misleading for some people and on some occasions
and of course CCR is relevant to any alterations to the exhaust port e.g porting.

As a very rough estimate, you may find on some applications that CCR is almost half than the "traditionally" measured CR.


P.s I believe some people have now "discovered" a way on how to reveal more HRC info?
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