just the block or the whole motor? the block is the same, there are differences in the pistons and maybe the head chamber configuration. the JDM motor has a bit higher compression, which in theory makes it harder to keep your motor detonation free. you would need a bit more fuel and bit less timing.
on the other hand, if it's all tuned properly and has a good fuel/timing setup, the JDM motor might make more power. even though the JDM motors are rated for LESS power than the USDM motors, they seem to make a little more.
10.0:1 is the stock CR on a USDM H22. 9.5:1 is hardly worth the trouble. 9.0:1 will allow you to run quite a bit more timing and boost.
on the other hand, you can certainly run 9psi at 10.0:1 CR. people run that much boost and more on engines with a stock 11.0:1 CR. it's just a question of the tolerances, the conservatism of the tuning, and having the RIGHT system for controlling timing and fuel.
from what other members here have said, below 9.0:1 the lude gets a bit sluggish off boost. my JRSC lude at 9.5:1 still felt strong off boost, so your mileage may vary.
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