As per the BMW 6 Series Enthusiasts companion, here's some facts on the M635csi: -Built 4/84 - 4/89 -Cast valve/rockers cover carried BMW letters initially, MPower for US and later 80's Euro models. -M badge on front grill and rear trunk; not M6 or M635csi. (US M6 did carry the M6 badge) -BATTERY WAS LOCATED IN TRUNK! -