After installing the JDM H22 (loving it by the way),i finally started to tear down the USDM h22a and after removing the head cylinders 2 and 3 have some sort of residue stuck on the pistons, anyone know what it could be?Its only on the middle two pistons and leakdown numbers before engine removal were 8%,22%,12%,7% respectfuly.

 

is it a residue or is it hard

 

its hard, i couldnt pick it off with my fingers

 

looks to me like its heat damage to the piston crowns, i've heard of piston crowns melting in places due to lean mixtures. was it pinking when it was running?

 

looks like your exhaust valves are making contact with the valve reliefs.

 

i would check your plugs, i would think it would prob be pre ignition as opposed to detonation but who knows, i bet your feeling lucky that you opened it before it went bang! P.S you haven't been doing any of those internet tutorials on ignition advance have you? sure fire way to break somethin if you ask me