wellllllllllllllllllllllli can tell you all my research has came back that the 8-valve 4G64 has a compression ratio of 8.5:1 with a 68cc combustion camber, not a 47cc and they use FLAT top pistons. this can be seen by simply putting the 2.0 8-valve and 2.4 8-valve head side by side. the 2.0 has a 47cc combustion chamber and you can tell that it is much smaller than the 2.4.

BUTTTTTT, when the 4g64 was changed to a 16 valve SOHC then the combustion went down to 47cc just like all the other 4g63/4g64 16 valve motors but the pistons have changed to a dish to lower the compression.