There are 4 variants of it.

3B - Only fitted in early S2 Coupes, has dizzy and different ECU
ABY - Late S2 Coupes and all S2 Avants. Has coil packs and more power than the 3B.
AAN - Early shape S4 and S4, pretty much the same as an ABY.
ADU - Fitted to RS2, various differences, but essentially the same as an ABY.

The UR Quattro (the original Quattro shape) has an ABY too.

All of the above are 20v, some early Quattro's had the I5 turbo, but are 10v (they are the ones that sound the same as the original Group B S1 when tuned!)