Originally posted by elbee
It's not all about compression. The 86 Integra and old SR20s had 9.5 compression and ran on regular. Probably had more to do with output per liter.
the F22/F23 motors were also 9.5 and required only regular.
it's due to dynamic compression. actual ignition timing plays an important role on the dynamic compression. the static compression is the compression with the piston at TDC. combustion happens after the piston begins to move away from TDC, not right at that moment... so if the piston is beyond TDC, actual compression is lower than the static rating. the further you retard timing, the lower the compression.
the H22 on the other hand has it's timing advanced more than the other motors mentioned.
so in all truthfulness, it IS all about compression... just not static compression.