ok, BEFORE YOU FLAME, i have searched, several sites, even this one and i ask the same question and get a different answer each time and i really want to true answer, matter of face i have asked this on this site before and couldn't get a straight answer, only post if you really know!

Ok, usdm b18c1 has 10:1 compression ratio
JDM b18c has 10.6:1 compression ratio which equates to the engine having 9 more hp..

Ok, so what is creating this higher compression? I have a jdm b18c in my car, so does my friend, and we have about 4-5 other friends with b18c1, so far, all heads say p72, i'm sure all the rod's, pistons, etc say p72 as well, at one time i "theorized" that maybe the jdm18c had a p73 bottom end since the usdm itr bottom end has 10.6:1 compression.. but when studying the differences in the head i realized that to be wrong..
So what is it causing a compression rise? does the jdm motor have higher compression pistons also stamped p72? in which you couldn't really tell the usdm and jdm apart? One person suggested a thinner head gasket, which i don't believe that because then everyone with c1 motor's would be just swapping head gaskets for 10 more horses..
I just find it awkward how i can't find a straight answer on this question... and besides curiosity, i need to know this in case i have to replace a part, such as head gasket, pistons, etc, so i will know to get the jdm part as opposed to a usdm part which would lower compression..

 

pistons hommie lol search??? theres this thing outside of ht i think its called google or something

 

Maybe is for the high octane petrol?? Maybe because if not there is no JDM stuff lol

 

http://www.ff-squad.com/tech/temp/pistons.htm

first result when i typed "jdm b18c piston" into google

 

ok, well seeing as how i don't know its the piston..... why would i type in jdm b18c piston?...... but thanks anyways.. that link is perfect..

 

well since the piston is the most common way to change compression i thought you might have considered researching piston variances between engines. sorry i if i assumed incorrectly. glad you found your answer.

 

yes i agree with that, but seeing as how both pistons say p72, that kinda scratched that theory for me, i did not realize there were sub marking on it -00 and -0A, and the fact that i have people saying, thinner head gasket, different head, different valves, different stroke, etc, then it leaves it wide open for me, because obviously all those people don't know either..