well i'm in the market for a new transmission.. right now i have the usdm S1 ls tranny, but i want to get the JDM S1 transmission.. i was curious if there is any way to differenciate between the 2 transmissions considering my usdm one says S1 and i'm sure someone in the past has passed off a usdm S1 tranny and told someone it was a JDM.

 

I think the only true ways to find out would be to either take it apart and count teeth or install it and drive around and see the mph vs. rpms.