I was under the impression that:

USDM:
RSX-S - K20A2
RSX (base)/Civic Si (EP3) - K20A3

JDM:
Integra-R - K20A


but then I was reading something and came across 'K20C'...I'm a little confused here. What car does this engine belong to?



Here is something else I found about it:
'n/a K20C1 JDM All 3-door Type-R' (civic)

 

K20A2 and K20A3 those two codes i read from Honda Tuner. However I also believe they mentioned that they were not too sure what the codes are.

But what I've learned from my Acura Book and also Honda's website, RSX type S engine code is K20C.

DC5 type R engine code is K20A for sure.
220hp @ 8000 rpm
Curb weight 1170-1180 KG
no VGS

the all new EP3 Civic Type R also uses DC5type R's K20A but with a bit les hp
215hp @ 8000 rpm
curb weight 1190 Kg
with VGS

I have a Japanese New Type R magazine (with all new NSX R , Accord Euro R, Integra R, and Civic R spec and test) , you can also find their info at Honda's Japan website

accroding to the test done by professional, Civic R has quick response, but Integra R is more stable.

lap time:
DC5 ITR
1:44:70
1:44:20
1:44:16

EP3 CTR
1:43:81
1:44:78
1:45:63