the honda civic 1.8 comes with a R18A1 engine..its a 1.8 litre engine churning out around 135-140 horses and a handful amount of torque, its a sohc
where as the b18 comes in different grades..most popular of them all are the b18c5 americano version and then there is the b18 type r the jap version..both are dohc cams..and they are more superior to the r18 in term of power and torque..although r18 has been awarded for being economical and powerful in the same shot and its pretty advanced as well
basically b18s are engines for performance and tuning, whereas r18 is a normal driving economical engine with a great power punch