No there was never an LS1 f -body rated at 340-350hp (except the SLP and Berger cars). The factory advertised rating on regular Zs, Formys, and TAs was 305 until 01 then it jumped to 310. In reality they all make 340+ at the crank.

 

thats what i ment, they were underated at 310-320 when we all know thats bs. 340+ crank easily. just about the same as the vette