Actually, I'm not sure about the existence of a C4, because the last time i checked all foreign b18c's had no suffix...just b18c, either spec R or sir-g, the differences were in the VIN's....

As for the C3, that is the designation for post production blocks, like if you were to actually buy a block from the dealership brand new. Thats why the spoon crate motors have the c3 designation, because they are brand new, not re-builds.

Hope that helps a little, if someone can prove me wrong, please do, i'm always up for some enlightenment :fawk: