Low drag 1275 piston standard size 2.780 (Rings included).
This piston has a possible compression ratio of 10.3:1 as fitted to Cooper RSP 1990.
The best performance 1275 pistons are C-STN100 range which have 9.73cr when the piston is 1mm down the block. . Current pistons differ from the 60s originals and now have a "low drag" slipper skirt design and a shorter lighter 20.6mm wrist pin. Wrist pin height is 1.5276" to crown with a top dish of 8cc.
Performance is enhanced by the use of 3mm oil rings and the smaller drain slot behind this ring decreases the risk of breakage and 2 of 1.5 mm compression rings. Crown depth to first ring is about 10mm
Rings are
R41570-00 AE Hepolite is now owned by Federal Mogul and trademarked "Nural"
Sold singly,4 per engine required--was Rover piston
TAM2050-00 stamped AE21963 as fitted to 1990 Cooper 1275 engines..Now Nural stamped 87-524100-00