:ugh:

Type-S pistons will require claychecking the combustion chambers to ensure fit. the H23 head has decreased compression chamber volume over the H22. valve angle is also different, therefore claychecking is VERY important as the valve recesses on the H22 piston may not be sufficient for use with an H23 head.

H23 uses dished pistons to create 9.8:1 compression. the H22 uses domed pistons for 10.1:1 compression. this is due to the H23's combustion chamber volume... i.e. the chamber roof is much shallower.

here's the deduction:

i have an H23 VTEC with H23 pistons. the H22 head with the H23 pistons creates 9.3:1 compression due to more chamber volme in the H22 head combined with stock H23 pistons... of which normally an H23 has 9.8:1 compression. a .5:1 compression loss.

the H22 pistons if i had dropped them in would have created 10.1:1 compression plus .5:1 compression due to the H23 head's reduced compression chamber volume. in other words, an H23 motor with H22 pistons would create a 10.6:1 comp motor. by sticking in the Type-S pistons, you'll end up a whole compression point higher, thus at 11.6:1 compression.

11.6:1 static compression will require fuel with a higher octane level than pump gas to run properly.