Bernie,

If you mean YB engines, then this is the information I have:

YBB - October 85 to July 89....18,990 produced (5,60 3dr and 13,390 4 door -250 excess to build requirements)

YBD - May to August 87......525 produced (RS500)

YBG - October 89 to November 91.......12,515 produced

YBJ - dates as YBG Euro 1504 emission standards (green cam cover)

YBT - March 92 to Feburary 94......5,186 produced (Escort Big Turbo)

Total units built (up to 1994) 36,691 (add 525 RS500 type for a total of 37,216)

My book (The Cosworth Fords - Jeremy Walton) was published
in 1994....so no further information. From then onwards
they produced the YBP (small turbo Es Cos) engine.