how do I blind eyed, tell that it is a JDM motor without doing a compression check? I found a SR20DE, and they say its a JDM motor, but how can I tell they aren't just lying to me?

Well remember there's different versions. There shouldn't be any emissions crap on it for one. It's a bit harder to tell the 10:1 motors though as far as I know.

Just look for egr stuff. If there is none then its a jdm.

what if its already in a car, and all the emission stuff should be there?

nope jdm has no emmision stuff on intake manifold

I understand that, but say its in a car, that is in a state that you need emmissions done, and the person swapped all the emmission stuff over to the JDM motor, from the USDM motor. Could you tell. Or is that just not something that you would need/want to do.

If someone switched the intake manifold then you probably won't be able to tell the difference.

ok