hi, thanks for getting back to me, yes I understand that the letter "Y" stood for pressure relief valve installed. all the smog pumps I have seen for 1969 Z/28 end in the letter "S". even in Jerry MacNiesh book the pump illustrated end in the date code with the letter "S" for Saginaw plant. so like I ask does anybody know if they know or seen a smog pump for 1969 Z/28 with a date code ending in the letter "Y"