Again according to RB Specs appendix.
CR options for A65s R/ L/ /LC 63- 65
9 :1 with the 64 R having an 11:1 option one year only, I can guess why that was deleted later.
65 -70 A65 T / L /
CR options 9 :1 with 10.5 :1 for SpitsMk 2 and Hornets.
66 -70/2 Spit Mk 3, Spit Mk 4 , Firebird, A70
all 10:1 except A70 9:1
A65 T , L, FS
with 7.5 :1 Low comp options.
What may have given the64 R/ 65 LC a better motor was the carb choice, twin , 389s with 1 1/8" chokes, the 66 L and H got 389/689 with 1 5 /32" chokes.its only a 1/32 difference , but the smaller carbs may have been more efficient?
Interestingly RB states the LC got a reversed cam plate to keep the gear change pattern with the reversed pedal. This was the same year the gear teeth form was altered.
" The most potent was the LC whose engine produced 51 [email protected]
,750 rpm " not sure why its 3 HP up on the L
since motor specs are the same, cams , CR etc.probably marketing propaganda. I dont think its the siamese pipe, IME they restrict top end.