Hello,

Let me raise a question about part numbers of pistons. I'm currently thinking of installing JDM pistons to my MY2000 S2000, as you know, they provide 0,7 more compression than the EDM or ADM. As I have a contact in Japan and Honda parts are freaking cheap over there (opposite to Europe), I'm struggling to get the part number of the pistons.

If I have a look in Hondapartsnow I find several references of piston sets (see attached picture). Can somebody enlighten me regarding this? Thanks a lot.

 

Whoa! Didn't know S2000 pistons were so expensive. $200+ per piston? Incentive to check oil level and watch the temp gauge.

 

Yes a set of 4 is typically close to 1k.

 

So, back to the OP's question: What's the difference between A, B, and oversize? Are any of them the same as the JDM F20 pistons? There's an A, B, and OS for the F22 also, and I wasn't aware the JDM F22 was any different. Also, my recollection (from WAY back, so I admit it's hazy) was that the higher JDM compression was due to a thinner head gasket, not different pistons.

 

B pistons are slightly smaller than A or no mark pistons. Oversize are a fantasy item that doesn't really exist but is supposed to be .25mm bigger piston. If you want oversize pistons you can only get them from Mahle.

 

What is strange is that all those pistons appear if I select a MY2000 S2000 (mine is F20C2). @Twohoos, the head gasket is supposed to be the same, even with the Spoon head gasket (which I already have on my car) compression only rises by 0,3, not 0,7.

 

$1k worth of pistons or $120 worth of a thinner headgasket...or better yet $50 worth of milling the head

 

Does that mean that B pistons give you lower compression ratio?
Which ones should I order in Japan for the JDM F20C?

 

They're smaller by .05mm meaning the no mark pistons are .05mm wider than the B mark pistons. You need a micrometer to tell the difference.