Actually the other way around. The small block Chev was called a mouse motor first, which led to the thought line "a bigger mouse would be a rat". The "mouse motor" term stemed from that age old battle of brand loyalty. It began when the Hemi folk started calling their engines "elephant motors" because of their large size. The sbc folk had pride in their engine's ability to make big power from it's comparatively smaller size. Thinking of the old wives tale about elephants being afraid of mice, the rag line resulted in the term "mouse motor".