I've had a B16A1 in my CRX for 2 years now, done all the work myself and know them like the back of my hand.(well almost Anyhow, I just purchased another B16A1 head on Ebay from a guy in Montreal, Canada (AY!). When I was ripping it apart to replace the valve train, I realized that it beared the mark "PR3-4". I cross-referenced it with my original B16 head and I reads "PR3-1". I know this is probably something real cheesy and unimportant, but I want to know if anyone know the differences in the numbers and what they mean. The only reason I ask is the fact they made a CRX in Canada with a B16a as well as Europe and Japan. I want to know if there are any differences between the Head (ie power,valve size, flow, etc.) or if the number difference is only for the region is was produced for.