if i have 2 fc 1 stock 1 not can i just switch the plates for one day and smog it or do they check vin #'s

 

There's a vin number on the cats?

 

They check the VIN...how else would the DMV know the test results are for that particular car?

You're only chance on trying to cheat it that way would be if you bring the ownership for the one you'retrying to pass, then see if you can get the tech use it for writing the VIN down, instead of the actual VIN tag. They might slip up, who knows.

 

yes they check the vin's that is the main number they need to input on the computer you can have a car smoged without plates but not with out a vin on it, because the vin will tell them what test to do california or federal and what options are in the car, like if it was a turbo or not