Is there somewhere online that tells how to identify rotors?? Compression ratio' markings on rotor etc.????

yep.



1st question, 10a 12a or 13b? 13b rotors are 80mm wide, 12a 70mm, 10a, 60mm....



12a rotors come in about 4 flavors



70-73 6mm apex seal, dual side seals, paper wieght material



74-76 3mm apex seals, combustion chamber is symetrical



77-82 same as the above, but combustion chamber is teardrop shaped, LEADING deep recess. they are different front to rear



83-85 lighter than the 77-82 rotors, they have a 2 letter stamp in the combustion recess instead of just f or r



13b rotors



74-83 3mm apex groove, 9.2:1 compression 12lbs



84-85 9.4:1 compression, not sure how to id these vs the older ones



86-88 NON turbo, 2mm cast combustion recess, its shallow.



86-88 TURBO, same as above but the combustion recess is deep (2" vs .5")



89-91 NON turbo, these have a fully machined face, 9.7:1



89-91 TURBO, same as the non turbo, fully machined, recess will be deeper



93-02 TURBO, same as the 89-91, but have a better rotor bearing



03-now, shallower apex seal groove, it has an extra cut for the oil seal protector ring, even shallower combustion dish, its very square too