Ok, 340's have a bigger bore '68-'71's came with forged pistons,forged rods,forged cranks,bigger cams much better flowing heads 340's only came with a 4-barrell or 6-pack induction and were underated h.p. wise anyone that has owned one knows that 275 was a joke number and yes the 22 c.i. is a big deal...performance wise i've NEVER seen a 318 beat a 340 in naturally aspirated form,not saying a 318 can't beat a 340 but you'll put more into it to do so...